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Henrik

HD Quality Video Transmitting

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Im in the pursuit of a video transmitting system capable of live streaming high quality video.

The project is going to be a closed circuit RC Car track.

So the range of the transmission is not that relevant as i can lay out recievers around the track(?)

The weight and size is also not that relevant since im going to be using a large scale vehicle.

Ive been looking at the video systems used in rc planes, but i dont like the bad image quality.

Is it really possible for me to achieve this?

I am willing to buy more expensive components to handle this sort of a job, but im not Bill Gates either.

Does anybody know where i could look?

Thank You very much!

Ps. If i get this project up and running, i will document it here the whole way.

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Are you really looking for HD (1280x720 or 1920x1080 high definition image from an HD camera), or "only" something SD (PAL/NTSC) but better than our common analog gear?

As a quick guide for HD you should aim for a $50k budget, for a broadcast quality digital SD system you can stay under about $10k.

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Hi Henrick

HD quality video – this is a project I am currently working on – let me share with you some of the issues that need to be thought through if you hope to implement HD quality video streaming successfully from a mobile platform (air or ground – makes no difference) to a fixed location ground station. This is a bit of a mouthful these notes, but they will once and for all cover the issues you need to bear in mind and think through if you hope to implement an HD video stream with any degree of real world usability on a moving model.

Camera

Camera selection: HD video means a camera with an image sensor with +/- 2Megapixels in one or other of the standard aspect ratio formats (16:9 or 4:3 been the most popular but there are others, like 3:2 or 2.39:1 … and a couple more). And of course there is the issue of PAL or NTSC. From the perspective of what you see on your computer or TV screen it makes little diff if you use PAL or NTSC – but in boarder-line processing cases regards what your video/graphics processor and/or onboard computer graphics chip is capable of handling, the issue of NTSC or PAL could just possibly become an issue – and I’ll explain why later.

The 2nd point to consider when selecting a camera is the type of image sensor it has i.e. CMOS or CCD.

CMOS image sensors, as a rule, do not produce as good a picture quality as do CCD image sensors. But, this is now starting to change – CMOS is many respects is catching up fast with CCD image quality, though no there yet. CMOS image sensors do though, as a rule consume less power, and provide more onboard processing options.

Last but not least is the image sensor pixel size and dynamic range.

The more pixels on an image sensor the smaller each pixel will be for a given image sensor size (obvious). The smaller a pixel is the less light enters it and the poorer the resultant video image will be. Double a pixels size and you let in 4 times as much light. If I was talking about SD (standard quality) video I wouldn’t raise these points, but in HD video they are important points. I’ll give you an example: I have one of Nikons very first professional digital still cameras that has a image sensor with just under 2Meg’s, but the picture it produces (for a camera made in the early 1990’s!) produces a picture of far far better quality than many tourist type 6 – 8 mega pixel cameras you buy off the shelf. Why? Because the pixels measure something like 10microns by 12microns in size (I forget the exact size now, but it’s along those lines) – versus the typical modern day 6 – 8Megapixel CMOS type digital cam, which has pixels of around 2micron in size.

So long as I am not having to produce pictures any large than around standard letter size (around 5” x 7” or 8” x 10”) then the picture quality from this close on 20year old digital camera is pretty much unbeatable. You’d be hard pressed to find a “point & shoot” digital cam with 4 – 5 x’s the pixel count that comes close to it in picture quality.

Where it is weak is in dynamic range – its real world usable dynamic range is not much better than around 64dB – 66dB. By comparison, many modern day point and shoot digital cameras (immaterial of pixel size) can boast dynamic ranges far in excess of this, and some of the best digital video and still cam’s can boast dynamic ranges in excess of 80dB. In simple terms dynamic range is range of light from dimmest to brightest, that the image sensor is capable of responding to. That, for all intents and purposes is what most folk need to concern themselves with as far as the sensitivity of a digital cams’ image sensor is concerned. If you wish to look at it in any greater detail, then the next thing to look at is the dynamic range noise figure of the image sensor.

In short, as far as choosing the camera component for your HD video stream goes, the mains points are:

- HD camera will have an image sensor around 2Megapixels in size

- size of image sensor – the bigger the better.

- size of pixels – the bigger the better.

- Dynamic range – the higher the better.

Analogue or Digital

In my personal opinion (and I emphasize – this is speaking for myself) it’s a no-brainer: digital is the way to go. Why?

Bandwidth Requirements

To transmit analogue HD quality streaming video you will require around 9Mhz bandwidth – and that assumes you are transmitting the basic version (or smaller version if you will) of HD quality video i.e. 720p/25fps (progressive type NTSC frames @ 25frames per second) versus 1080p or i/30fps (interlaced type PAL frames @ 30frames per second). 1080 p or i (as either NTSC or PAL) is going to give you a better picture but will use more bandwidth as an analogue transmission – around 12Mhz. With those 2 figures in mind Henrick one now has to consider the rf transmitter power requirements. In short, while the area requirements you have indicated are not excessively large, the wider the transmission bandwidth, the greater the average transmitter power requirement will be, and the larger therefore your battery pack will need to be. This last point (i.e. regards required power) is a comparative statement – its relevancy will become apparent a little later on.

Digital

By contrast transmitting an HD digital video stream will require no more than between 4.5 – 6Mhz of bandwidth – subject to compression rate and type of compression used.

Why not transmit uncompressed digital video?

For no other reason than an uncompressed digital video stream will require as much as 40Mhz of rf bandwidth and will consist of something like 400Megabits – 1.5Gigabits of data per second!!!

While that’s not impossible, its way beyond the cost and required processing scope of the average amateur hobbyist – in fact, there aren’t many PC around that are able to process info at 400Megbits – 1.5Gigabits real time/low latency, never mind the latency that will fast build up and accumulate the moment you start trying to shift and modulate all that data for transmission over the air.

So it has to be compressed – simple as that – no ways round it currently. 10years time, ask me the question again and I wouldn’t at all be surprised if a solution existed, but not now.

There are 2 practical choices for compressing live streaming HD video: MPEG2 and H.264. Both can do the job, but there are many differences between these 2 codec’s. From an amateur hobbyists’ point of view, as far as MPEG2 and H.264 goes, the main points to consider and bear in mind are as follows:

a) For an equal picture quality, H.264 will require less bandwidth than MPEG2, but will require greater onboard processing power (H.264 requires more processing and uses more onboard power for the same picture quality).

B) For equal transmitted bandwidth used, H.264 will produce a better quality video stream picture.

c) For equal transmitted bit rate, H.264 will give you a better quality video stream.

There are a dozen different ways in can be written down, but in short: H.264 requires more processing to prepare for transmission, but will give you a better video stream and final video picture. What determines just how much processing is required onboard, and just how much time is taken up (that all important consideration when transmitting video – latency) is what codec is chosen.

The thing to keep in mind about both MPEG2 and H.264 is that they are codec standards more so than codecs i.e. how well an individual codec actually functions (i.e. how fast it is, how much processor power it uses/requires and how good good a picture quality it produces for a given bit rate and latency) is largely down to how well an individual codec developer has taken the MPEG2 or H.264 codec standard, and set it up and refined it for a given application. Consequently, you get good MPEG2 and H.264 codec’s and you get poor MPEG2 and H.264 codec’s. Codec's can be setup by developers for dyanmic secnarios, or if the application is static low light vision, a developer can set the codec up for scenes that contain a lot of repetitive image data - tweak the codec for optimisation for that sort of application and sacrifice the processing aspects of the codec that concentrate on fast changing dynamic scenes. By the same token, in low light applications, the contrast ratios can be emphisized at the expense of colour depth ratios ..... etc etc. How well a chosen codec functions in a given application is how well the developer understands the codec standard and how well they have taken the standard, and applied it to the clients' proposed end-use. Understanding codecs to this depth is a very specialist subject, conseunqetly most off-the-shelf codecs that come with hardware products are codecs that are "averaged out" so to speak i.e. they are setup to cover as many difering scenarios as the product is likely to encounter. The few HD MPEG2 and HD H.264 codecs I know of that are developed specifically for live TV from helicopters down to groundstations are horrendously expensive codecs - and are bound up with IP protected hardware. Well out of the hobby price range.

Just keep in mind that not all MPEG2 and H.264 codec’s are equal - get as much detailed info as you can about the codec - and the options avaliable with any firmware supplied with the codec that allow the end user to make fine adjustments (which decent codecs do allow for).

Last but not least as far as codec’s are concerned, both MPEG2 and H.264 can be implemented in software, or they can be implemented in hardware (i.e. using a dedicated IC/chip/ASIC). As a rule, hardware implemented codec’s produce a better picture for a given latency – overall they are quicker & better. An example of a superb, almost professional studio quality H.264 codec that comes with low single frame latency is Black Magic’s H.264 USB dongle codec. I use it – set up properly its speed and picture quality is mind-blowing good. Okay, its $350 dongle, but if you want good quality HD video at latencies that are acceptable for use in real-time control applications, you’ll be hard pressed to beat this one. There are others, I know of another H.264 hardware implemented codec that’s runs at sub-one frame latency, but its price is something like $6000. Great – but not practical. There is another HD hardware implemented codec coming out in December – it to is going to be sub- one frame latency, but its been made specifically for mil use, and although it’s going to be under the $500 mark it is going to be offered only in PC104/plus card format – meaning: not much good unless you are running PC104/plus BUS/frame as part of your model.

That pretty much sums up the points to bear in mind about the codec component part in any HD video setup you are thinking of implementing. If you are wanting to implement a real world usable video stream that “does what it says on the tin – and does in properly”, then the above are points that need to be thought through and kept in mind when it comes to selecting whatever codec you intend to put to use.

On a similar but related topic, I want to expand a little on this whole subject of latency i.e. the time that elapses from the image sensor seeing something, to the time you actually see an image on your computer monitor or TV screen.

Total latency is made up of a number of processes – it’s not only the time it takes to compress a video stream. Onto this time has to be added the time it takes to convert a video image to digital – and there is no such thing as a digital image sensor, they are all (without exception) analogue to start with, as well as the time that it takes to modulate the digital video stream (e.g. COFDM modulation), then the time it takes to break the video stream down into little packets of digital data and spread these packets out if one is using spread spectrum, then there is the time it takes to encrypt/cipher all the digital info (in encryption is been used, s is often the case with 802.11 IP streams). Then on the receive end of the link, all these previous processes have to be “reversed” for lack of a better word, which more-or-less doubles the time though in reality most folk will have slightly more processing power at the ground station so will be demodulating/decrypting and converting back to analogue, a little bit bit quicker than it takes to get it all set-up in the first place.

The point to keep in mind though is that, the latency quoted by a codec designer/manufacturer, or the latency quoted by an ADC manufacturer is always only part of the total latency that a FPV flyer is going to experience. To get a total latency figure of any usable accuracy requires establishing all the individual latencies for all the processes at both the transmit and receive ends of the link, and adding them together correctly. In reality, real-world total latencies that are been experienced today by folk using decent HD video streaming hardware & software in rf link scenarios varies from around 80millsec’s – 200millisecs in total i.e. 1/10sec to 1/5sec. Still, I don’t think that’s bad when you consider all the stages a bit of data has to go through to get from a camera image sensor to a computer/TV display.

Analogue to Digital Conversion (ADC) rate

The spec to look for here, is the analogue to digital [conversion] rate i.e. how often per second (usually in Khz) changes in each image pixel are noted and used e.g. the pixels output voltage (which determines the colour that the pixel resolves and why I said earlier that all image sensors start out the job they do in analogue as opposed to digital), and at what resolution are those readings noted ( usually in bits – e.g. 8bits,10bits,12bits … or whatever). Typical sampling & bit rates for an HD analogue to digital conversion are along the lines described above i.e. 8bits, 12bits, and 16bits 24bits …. 32bits …. and so on, and typical sampling rates are 32Khz, 48Khz … and so on. The more often these readings take place & the finer the resolution at which they are recorded, the better the resultant video picture colour, contrast and other parameters that make up picture quality, will be.

This process takes time

Modulation

The next step in the process is to modulate the digital data for RF transmission and there are a 101 different modulation schemes that can be adopted when it comes to transmitting any video, let alone HD video. This is the digital part from the RF transmission point of view.

COFDM is one of the more common modulation schemes, and is used so much because of its unique resistance to delays and fading problems associated with RF transmission – more commonly known as multi-path problems. An excellent intro to COFDM modulation can be found at:

http://downloads.bbc.co.uk/rd/pubs/reports/1996-08.pdf

…….. so I wont bother with any notes on this part of the overall process

Amp Stage

The last consideration to keep in mind when it comes to transmitting digital content with wide band-widths and lots of data content (and HD video transmissions are about as dense as you get) is the linearity of the amp stage. I wont say much here because quite frankly, I don’t think you are going to need much in the way of amplification – at least as far as the application you have described goes.

Linear amplification is critical when it comes to digital data content. Without excellent linearity data quickly gets distorted in both phase and amplitude, rendering it unrecoverable on the receive end. Even the best Class A type RF analogue amps struggle to maintain sufficient linearity for use as digital video amplifiers. Digital RF amps should be designed from the start as digital content amplifiers – using an analogue rf amp will usually end in tears.

When it comes to amplifying IP/802.11XX (i.e. WiFi) the requirement for linearity in the amp stage is even greater.

Typical Gain flatness figures required across the full modulated bandwidth of +/- 5Mhz in digitally encoded HD video signal, or the 10Mhz – 20Mhz band width of z 802.11XX signals, at max power output needs to be somewhere around 0.3dB – 0.5dB – never mind the rms/average output required Gain flatness (the all important figure), which will be much lower than that. Fairly easy to implement when your power output is something like 10mW, gets progressively more difficult technically, as power output increases.

In short, if you want to setup a digital HD video stream from your flying model to a ground station, there are a whole bunch of points to consider when it comes to selecting what gear to use – if you want to retain the HD video stream quality that it is possible to get with HD hardware. Get any one component in the chain wrong and you’ll land up with picture quality little better than SD.

Note – HD video is about to burst onto the UAV scene at the military level. USB dongle sized pro picture quality H.264 engines exist (e.g. Black Magic’s $350 H.264 USB engine – small enough, light enough and power conservative enough to use in most flying models). The choice of board camera’s and block camera’s is endless – from Omni Visions 100dB plus dynamic range board camera’s with auto contrast (meaning you can fly into the sun with it and ground based detail in the lower half of the screen will not be blacked out), to Sony’s H10 and H11 block cameras (although these are a bit above the average hobby flyers price range). Adaptive RF make a range of small COFDM type RF amps that suitable for digital video (http://www.adaptiverf.com/Products.php).

Try searching Google images for small digital video modulators & transmitters - type “low power OEM COFDM video transmitter” – quite a selection comes up. The RF stage for digital video remains the most expensive component in any set up, as till now it’s been the preserve mainly of the pro community, but that is going to change over the next 24 months or so as HD IP based video content gets better and better faster and faster in terms of picture quality. I don’t think it will be long before HD band-width capable small low power digital amps cost little more than analogue SD video amps cost.

Eventually everyone will be wanting to use HD digital video. There is a good argument that says all digital video links will need to be spread spectrum to avoid conflict and interference issues

IP based HD video systems may ultimately be the way the mass market goes – not withstanding the transmit power limits, and therefore range limitations. In 5 – 10 years time we’ll probably have 4G mobile phone modules that can handle full res HD video on reliable data links

Implementing digital HD video is great – the practicalities will be a little more involved when it starts to take off, and for the time been it remains comparatively expensive to implement stand alone HD digital video transmission with the same degree of reliability and range as SD analogue video - no way round it.

Right I’ve said enough now. There isn’t much to choose from out there at the moment when it comes to digital HD video, but what is out there needs to be studied carefully before making any choices.

The short cut to all this is to simply go out a choose an IP ready HD video camera i.e. a video camera that broadcasts a web ready stream of data – and set that up as your cam. In reality, my experience with these products is latency – they are not easy to setup with suitable low latencies for real time model control/command, because the MPEG2 or H.264 codec’s they are shipped with are not codec’s designed/configured for real-time command/control purposes.

Picture quality though, can be surprisingly good.

Long winded, but I hope you find it useful. Theres a lot to be thought through when it comes to implementing low latency/”real-time” video in any command/control set-up – and it becomes exponentially more involved if it’s HD video one wants. Not impossible, but it needs careful thought and careful choice of components.

Good luck - and ask if you have any questions (that is after all what forums should be about)

Patrick

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Patrick,

That is quite a dissertation on elements of HD Quality Video Tranmission. Although you mention COFDM, I think it is important to note that the DVB-T COFDM based implementation is optimized specifically for the RF path and low latency required for HD FPV. Since DVB-T is now the standard for European RF transmission of HD video, low cost receivers are already available. There is still the problem of low cost/small sized units on the TX side but almost certainly this will become available in the future. DVB-T based FPV systems are already available at military level prices:

http://www.advmw.com/uav_cofdm_transmitter_c2lt.html

I've actually considered buying a TX/RX system from these folks but at $20,000 for the pair, I think I'll wait a bit longer. It is tempting considering the level of performance this system provides:



  • HD video with 3 to 5x range of a typical SD analog video TX link (for same power)
  • Complete mitigation of multipath
  • 60 to 70 ms for total latency
  • Resync in 10 ms or less

With that level of performance I could almost be tempted to buy the units. However since I now get nervous flying my $2,000 quad a couple of miles away, I would probably be sweating bullets flying the $12,000 quad side of the link. I tried to convince the Advmw sales guy that a demonstration of their system flying on a quad copter would be good advertising. Unfortunately they didn't go for it. I hope I'm not VOMM (Very Old Man Mike) when low cost units finally become available.

OMM

Edited by Old Man Mike

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Why not transmit uncompressed digital video?

For no other reason than an uncompressed digital video stream will require as much as 40Mhz of rf bandwidth and will consist of something like 400Megabits – 1.5Gigabits of data per second!!!

While that’s not impossible, its way beyond the cost and required processing scope of the average amateur hobbyist – in fact, there aren’t many PC around that are able to process info at 400Megbits – 1.5Gigabits real time/low latency, never mind the latency that will fast build up and accumulate the moment you start trying to shift and modulate all that data for transmission over the air.

So it has to be compressed – simple as that – no ways round it currently. 10years time, ask me the question again and I wouldn’t at all be surprised if a solution existed, but not now.

Actually, the only affordable HD wireless transmission systems that exist today, and are available as off the shelf consumer products for around $500, transmit uncompressed video ;)

Have a look for wireless HDMI transmitters. They are meant for sending an HD signal between HDMI devices that are in the next room, or a beamer on the roof where you don't want to send cables etc.

Where they're unsuitable for us is the range, as that's limited to 10 or 20m, and they're big set-top boxes. All the rest is great as there's no loss of quality and zero latency (they're often advertised for using with game consoles, where a delay would be even worse than for FPV).

But I'm somewhat thinking the OP was looking for a practical solution more than for a technical course ;)

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Thank you very much guys! This has been tremendous help.

I have to look into the oppertunities to see what suites my project.

Very excited! :D

Ill be keeping you up to date with what i find out :)

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Kilrah

..... indeed, the OP was looking for a practical solution. Off the shelf solutions to implement "connect & fly" HD streaming video are thin on the ground so far as finished products suitable for hobby use go. Most of what does exist (currently) is either too expensive or too bulky.

A possible way forward would be to seek out suitable parts at a component level i.e. put together ones' own system from separate off-the-shelf parts. To do that successfully would mean keeping in mind the points I raised.

As far as HMDI goes, the points I raised are as applicable to HDMI as they to any other HD video setup. I have read through Wireless HDMI standards - in its most basic form its an 802.11(x) solution, and if one wishes to consider any of the other Wireless HDMI solutions (at chip level - where is where one would need to start if seeking out a package small enough), they are as likely to run into frequency, bandwidth and power issues as they are attempting to hack any of the other digital ISM band standards.

HMDI is no more, or less for that matter, an option than any 802.11(x) type setup would be – it will not be exempt from the issues I raised. And it certianly is not latency free, although granted for all intents & purposes it's capable of very impressive latency - although I do note that many published HDMI latency figures are often published in a similar way to how 802.11(x) data throughput rates are published i.e. one needs to appreciate the conditions for which the data throughput or latency figure is published e.g. data throughput for HDMI in 802.11(x) format (which is one of the common HDMI standards used) is given for the transmit dB level - the lower the power level the higher the throughput, the higher the transmit power, the lower the throughput. Similar "conditions" apply to latency, and these need to be taken into consideration for a published latency figure. But - yes, granted, very low HDMI latency figures are realisable. There is one practical problem with off-the-shelf HDMI systems. Almost all come off the production line with permitted ACK bit timing configuration that limits the overall distanc eover which they can be used - quite immaterial of the amp power one has avaliable. Here again, is another example of a component characteristic that will need to be understood (and changed) when using parts to build up a transmit system. Some HDMI products can be tackled at kernel and firmware level - subject to ones ability with C+, Python ... Linux or whatever programming enviroment one is comfortable with. The ACK bit* timing is almost certainly going to have to be changed in the firmware if you hope to use HDMI over any real world usable RC model flying radius.

In short: HDMI is no more a off the peg solution for use as an HD streaming video solution in RC model/hobby applications than any other HD option is currently.

The practical solution at the moment so far as I can see, is to tackle HD streaming video “problem” at chip level – to do what Daniel Wee and Thomas Scherrer have done in respect of long distant control links i.e. take one of the dozen plus industry standard receive/transmit or transceiver chips and design & build around it a transmit/receive solution to whatever standard one chooses to adopt. After all, at chip level complete transmit/receiver and transceiver solutions do exist in packages measuring no larger than a ½” x ½” – it’s just that to date no commercial solution is available off the shelf for hobby use, only I suspect, because at the commercial level I don’t think the market volumes would justify the development time & effort that would need to go into such a solution. But make no mistake, it is possible and its by no means technically a difficult thing to do.

So, although I did not offer Henrick a solution to his question, Kilrah, I like to think what I took the trouble to share with him (and anyone else interested), is at least some of the issues that need to be thought through if trying to put together an HD streaming video solution from parts at component level. You are of course free to take it for what you feel it worth.

As far as cost goes, off the top of my head, I believe somewhere around $2k - 3k makes it possible to put together a basic digital HD streaming video transmitt system - from careful and selective choice of components, and by basic I mean a transmitt system that will offer real world low latency HD imagery, and is "mass/volume/power consumption" compatible with a medium to large RC model. To do so will defineatly require some understanding of what is involved, and taking into consideration many of the points I raised in my initial note. Good luck trying to do it otherwise.

As to how "universal" such a system will be is very much up to the legislation as it applies to frequency, bandwidth and transmit power where you reside. In any event $2k - 3k can do it. Not really a cost amatuers would be happy with across the board, but certainly accetable to any committed/determined hobby FPV flyer.

As a side note Super High Def now exists. This coming Sunday I am going to see a BBC/NHK demo of this technology.

Some basic spec’s: the camera/image sensor produces an image which is just over 4k x 8k – some 16x's current 1080i HD image resolution which means a data stream of some 24Gigabits per sec!!

That gets compressed down to 1.5Gigabits per sec (don't know the codec used, MPEG2 and/or H.264 I would doubt very much have IP cores capable of handling those sorts of bit flows), and then IP encapsulated to 350Megabits per sec for sending over the internet!! I look forward to seeing just how they do this - the demo will include IP transmission to a studio in Japan.

One of the 3 existing Super High Def cameras is going to be used to record selected events at the 2012 Games in London.

The figures are just … well, you can only shake your head thinking about it, but the BBC and NHK (the developers of this technology) are pretty confident that it will be commercial technology available to you and me sometime over the next 10 – 12years!

That says something about just how fast video/IP/transmitt technology is moving forward. You have to wonder if its worth bothering with common ol' HD!

____________________________________________________________________________________________________________________________________________________

* ACK bit - the code in 802.11(x) firmware, and similar digital hardware/software links used to control the time period hardware/software will wait before ignoring a data packet, requesting retransmission, moving on to the next receive/transmitt task, timing out .. or whatever the link is set up to do. Its measured in micro-sec's and has a big impact on the performance of digital links when used in transmit application longer than they were designed to be used in (HDMI is designed almost exclusively for use over short distances e.g. 10m - 50m or so - certainly not RC model flying distances).

Edited by Helix1

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The practical solution at the moment so far as I can see, is to tackle HD streaming video “problem” at chip level – to do what Daniel Wee and Thomas Scherrer have done in respect of long distant control links i.e. take one of the dozen plus industry standard receive/transmit or transceiver chips and design & build around it a transmit/receive solution to whatever standard one chooses to adopt.

[...]

As far as cost goes, off the top of my head, I believe somewhere around $2k - 3k makes it possible to put together a basic digital HD streaming video transmitt system - from careful and selective choice of components, and by basic I mean a transmitt system that will offer real world low latency HD imagery, and is "mass/volume/power consumption" compatible with a medium to large RC model.

Yep I agree about that - but my point is that your $2-3k would be material cost, and once you add the few thousand hours of work such a project would need, maybe your device will be smaller than the current commercial offerings - but certainly not cheaper if you have to spread that development time over a couple of dozen interested people. Making an R/C system by reusing chips like you mention is a piece of cake next to treating HD video. Maybe tackling the transmission chip is at the same level, but converting a PPM frame to a digital value and sending it out is a matter of an hour, while handling the real-time, efficient and low-latency compression of an HD video signal is a mountain in itself in complexity and also hardware (expensive and difficult to obtain).

Daniel and Thomas, as people who do that as a side activity, have taken approx. a full year to develop their R/C solutions. I just can't imagine someone in the same situation manage to develop a wireless HD tranmission system in a decent timeframe.

I'd love to be proven wrong though, if you think you can do it... ;)

Edited by Kilrah

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Yep I agree about that - but my point is that your $2-3k would be material cost, and once you add the few thousand hours of work such a project would need, maybe your device will be smaller than the current commercial offerings ...

And at $7.25 minimum wage the total cost would be around $25K (more like $150K if calculated as real engineering cost hours). That makes the currently available ADVMW system a bargin. And I'm quite sure the ADVMW system would have latency and RF link performance well beyond anything pieced together from off the shelf commercial ICs & processors. Custom ASICs and/or FPGAs are currently required if you want to achieve anything close to the ADVMW system performance.

Patrick, if you are really serious about developing something for HD FPV, I strongly recommend that you study DVB-T in detail.

OMM

Edited by Old Man Mike

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And at $7.25 minimum wage the total cost would be around $25K (more like $150K if calculated as real engineering cost hours). That makes the currently available ADVMW system a bargin. And I'm quite sure the ADVMW system would have latency and RF link performance well beyond anything pieced together from off the shelf commercial ICs & processors. Custom ASICs and/or FPGAs are currently required if you want to achieve anything close to the ADVMW system performance.

Patrick, if you are really serious about developing something for HD FPV, I strongly recommend that you study DVB-T in detail.

OMM

Sorry Mike - I'm obviously missing something in what you trying to share with me.

What is it about DVB-T (as opposed to say DVB-S, or any other transmission standard/modulation that could be applicable to HD video) that you feel I don't understand, or have failed to keep in mind with respect to the notes I written regards HD video?

..... and the point regards AMPS products - I'm missing on that as well?

Thanx

Edited by Helix1

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Its an interesting disscussion and way over my head at times but is it worth all that time and money? I admit HD would be nice if the price was low enough but for me on board recording is the way to go. Unless you need a live feed for a live broadcast it seems just too much trouble at the moment. The down link to me is just a way of aiming my still or video camera and to give info via the OSD.

If you have the time and the money then go ahead its all very interesting :D

Terry

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Its an interesting disscussion and way over my head at times but is it worth all that time and money? I admit HD would be nice if the price was low enough but for me on board recording is the way to go. Unless you need a live feed for a live broadcast it seems just too much trouble at the moment. The down link to me is just a way of aiming my still or video camera and to give info via the OSD.

If you have the time and the money then go ahead its all very interesting :D

Terry

No Terry, it isn’t worth it financially. The costs and technical barriers over-ride the advantage in all but a few cases – which is why the few low latency HD video streaming hardware packages that do exist and are small enough to squeeze into a model (and it would need to be a model of fair size) cost so much (economies of scale).

I don’t know what the policy is in other companies, but EADS sees video sensor systems and links for UAV platforms all been HD within 3-5 years, and in a broader context, trade publications for the digital cam & image sensor markets by and large concur that within much the same timeframe HD image sensor production is going to overtake SD image sensor production. SD video is going to become to the mass-market what “black & white” is to television today. Note the comment my previous note regards HD and the technology that is now just starting to be tested (Super High Def)which will replace HD – that within the next 10year or so HD itself is going to be out of date - consumers will be using image sensors/digital cameras with resolutions and bit rates that top of the range PC hardware cannot come close to handling today.

At the moment, nope it’s hard to justify on a commercial basis – but that is changing fast and with it is going to come the drop in cost that comes with digital products as they catch on more and more with the mass market.

It’s very much an experiment to demonstrate its possible technically, and for cheaper than I think is realised (keeping in mind the conditions I stated earlier regards one-offs versus series production of any kit for hobby users) – but I agree, it’ll be at a cost that one is very likely to look back on in 3 – 5 years time and laugh at (i.e. leave it another few years and it will be as easy and as cheap to do then as it costs to implement SD analogue video today). Anyhow, much of what we do and spend when it comes to model flying offers little return – we do it for fun & enjoyment.

Edited by Helix1

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Sorry Mike - I'm obviously missing something in what you trying to share with me.

What is it about DVB-T (as opposed to say DVB-S, or any other transmission standard/modulation that could be applicable to HD video) that you feel I don't understand, or have failed to keep in mind with respect to the notes I written regards HD video?

..... and the point regards AMPS products - I'm missing on that as well?

Thanx

Earlier this year I did a detailed study of possible digital waveforms best suited for FPV HD video. There are a lot of things to consider such as interleaving interval compared to mulitpath delays, resync time vs BER and encoding/decoding vs processing delay. Bottom line is that DBV-T appeared to be the best balanced when considering the four primary performance areas for HD FPV video waveform:

1) Total System thruput delay

2) Good performance in low S/N

3) Good performance in mulitpath

4) Low resync time

When I found the referenced AMP design implementation, I felt that their optimization of the DBV-T basic waveform was a near perfect solution. After being involved with military spread spectrum communications for over 25 years, I can appreciate the research and development that went into that product. Sorry if I appeared to cast doubts on your knowledge in this area. I just felt the suggestion that a good FPV HD system could be done with $2K to $3K worth of components is a bit oversimplified.

OMM

Edited by Old Man Mike

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Okay – OMM, now I’m with you.

I’m not sure though I concur with you that there is anything unique about AMP’s COFDM modulators, and with great respect OMM, that this isn’t apparent to you suprizes me somewhat in view of your 25yrs experience with SS.

Actualy there is one thing unique – it’s the price (mind you, so to are L3-com’s small/portable COFDM modulators - in fact L3-com’s products cost even more!).

I’ll explain myself.

Off the top of my head I can name a half dozen or so brand-name pro-spec clip’on sized COFDM modulator manufacturers – the small modulators that broadcasters give to crews to clip onto the back-end of their field broadcast cam’s – and that, from a modulation perspective, is all the AMP product is. I see nothing modulation or transmission wise in AMP’s COFDM modulators that isn't typical of clip’on broadcast spec'd COFDM modulators – and these come in at around $3k to $5k (for top end models)! They can often be picked up on eBay or from specialist trade dealers, for around $1k. In fact looking at AMP’s COFDM spec versus say BMS’s CT2200HDV or CT-Series, or Nucomm’s CamPac2 Pro/News, they can be purchased for around ¼ to 1/3 to what an AMP modulator would cost and they cost a darn side more to manufacture & package* - and, these broadcast spec’d modulators offer HD capable bandwidths (which AMP’s products do not).

That AMP, L3-com, DRS, Schneider, BAE Systems, Cobham and other manufacturers who make small wide-band COFDM modulators suitable in terms of size for the UAV market, price them around $15k – 20k, does not reflect unique intellectual property, or capability – though some of the advanced UWB COFDM modulators used in missile telemetry do run unique IP cores (which do require considerable time to research & develop), they are by & large straightforward mature COFDM products.

They are expensive because of the economies of scale associated with running companies that centre their product, marketing & sales around defence & law enforcement type organizations versus broadcast type organisations – not because the COFDM product itself that they offer is any better or the technology any better.

Don’t apologise for casting doubt on my knowledge or anything I claim – I’m quite comfortable with that. If I make a statement on a public forum, you have every right to ask me to put my money where my mouth is. You're not going to catch me contributing on a subject I don;t know about, but don’t hold your breath – Xmas is still a bit of a way off, still, I should have completed putting together the components by then to demonstrate real world HD COFDM modulated low latency video transmission by then, that is suitable in terms of power requirement and mass/volume for installation on a medium/large UAV – and for around 2k – 3k (cost) – using COTS components. I’m confident I can do this and have not oversimplified the project.

Edited by Helix1

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Okay – OMM, now I’m with you.

I’m not sure though I concur with you that there is anything unique about AMP’s COFDM modulators, and with great respect OMM, that this isn’t apparent to you suprizes me somewhat in view of your 25yrs experience with SS.....I’m confident I can do this and have not oversimplified the project.

OK then. I shall be the first to buy your system at $2500 which at least meets the size/weight form factor of the AMP system and provides at least ALL the following:



  • HD video with 3 to 5x range of a typical SD analog video TX link (for same power)
  • Complete mitigation of multipath
  • 60 to 70 ms for total latency
  • Resync in 10 ms or less

I'll even give you twice the time you suggested, say March 2011.

OMM

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I click the "Buy" button too for same specs.

Nobody has talked about I/O yet, obviously HDMI and HD-SDI are must haves.

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Nobody has talked about I/O yet, obviously HDMI and HD-SDI are must haves.

And since I would beg to be a retailer for such a system, USA regulatory approval is a must-have too. FCC Part 15 registered, please. :)

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I made it clear earlier that to tackle a digital HD system for ones self is not the same as tackling the project – especially as a “proof of concept” project - from a retail ready perspective. Putting together this system, as explained in earlier, is not only a technical exercise but needs to be cost conscious. I may source one or other component as a used component from a specialist dealer e.g. the codec engine (Black Magic H.264 Pro Recorder) I sourced today as a used part from a specialist broadcast equipment dealer in London – saving the equivalent of just under $100 (retail price in the United Kingdom is around $500 equivalent).

As far as an HD camera goes .. well, there are hundreds of options that could be used e.g. I have looked at a Sony H11 which offers both digital as well as analogue output – and Sony makes a decent HD-SDI interface board, and there are other 3rd party manufacturers of interface boards for just about whatever option one wants. The used example I looked at was priced up at just over $600 equivalent. I’ll hang fire on that for the time been – no rush lots of options to choose from. The point is, and I explained this in an earlier note: demonstrating the concept with used parts is one thing, offering the same thing on retail basis for the same price is another thing. For a start, as a proof of concept project the rf modulator I decide to use may well be legal for use in say, South Africa, or Australia, but may not be legal for use in say the United Kingdom or the USA, from a power/dB level output, or possibly the frequency.

So, saying “I’ll press the “buy” button”, but it must satisfy this regional power output, bandwidth, frequency ….. or whatever other criteria you choose to use that is applicable for the country you, or whoever lives in, is … … well, go figure it out. I covered this point as well in one of the earlier notes I posted on the project. This proof of concept undertaking is to demonstrate that real world usable HD video streaming is possible - both technically and cost wise at a hobby level. I went on to explain as well what I meant by cost wise i.e. that although 2k – 3k is not what the average FPV hobby flyer would tolerate, it is a cost a determined/committed hobby flyer would be fine with, and judging by what some folk have said it would appear that even if it was more than that, it would be acceptable.

Okay – does the difference between a commercial project and a proof of concept need to be explained any better?

Okay – lets move on to some of the technical criteria that all of a sudden have to be satisfied - not with standing that they too were explained earlier in one way or another …… what’s happening here is that certain folk have tried to challenge me from the start on this project, haven’t really added much of relevance, so try to subtly move the goal posts …………… ?

Okay – let’s start with Old Man Mike’s requirements!

OMM, you rattle off a bunch of criteria, not with standing what I covered or explained in earlier notes, or what you should know with your 25 yrs of SS experience, you rattle off a bunch of criteria that are technically vague or impractical, or disregard what I explained or covered earlier

Size/Volume – must at least meet the size/weight form factor of the AMP system

I covered this earlier – I said it believed it could be done in size/mass/weight/volume for a medium to large sized model – and I went on to qualify that in broad terms alone the lines of a 2m wingspan sized model. RC model of that size are common and practical. I am not going to commit myself to this or that size, other than that it would suitable for installation in a model of around the size I have already stated. I also explained what could be satisfied in terms of power requirements i.e. the system would be practical for the power a medium/large model could provide. Couldn’t be clearer.

Complete mitigation of multi-path?

Nope can’t satisfy that requirement – in fact, I don’t know of any HD downlink streaming video system that offers complete mitigation of multipath interference or problems in moving situations that rely on an rf link that has no control over the environment in/over/through which it has to transmit. It’s just not practical.

I phoned a long standing friend of mine who works for the BBC’s Research & Development section – he has 40 years experience with microwave video links. I asked him if complete mitigation of multipath interference was possible for a COFDM modulated video link that is constantly on the move, as would be the case in a video link from a flying platform to a static ground station. Not possible – period. Let me qualify that statement.

You can model multipath interference solutions with very very good results in fixed situations (i.e. for where both the transmitter and receiver are static). Multipath in situations like this can be characterized by the geography of the land over which the signal travels in different directions, as well as the height and location of buildings, bridges and other man-made features within the area of coverage. COFDM modulated transmissions in scenarios like this can be modeled accurately, enabling operators to choose/set and make use of many user defineable characteristics of COFDM modulation that allow for configuration & setup to be tailored for given link conditions. Coupled with this benefit are the benefits that can be derived from careful choice of aerial type and radiation pattern, to further reduce the different forms of multipath interference – both at the origin and destination of the link.

Tailoring COFDM modulation and choosing antennas and hardware for multipath environments in static situations can indeed allow for very very good results i.e. min multipath interference to the received and displayed signal. But, it’s a very different scenario for any rf link for which the environmental influences on signal propagation are as variable and constantly changing they way they do for air-to-ground type links that are constantly on the move, and secondly, for which there are practical limits to antenna type and setup that can be used, as is the unavoidable case for the applications we are talking about. The variables are huge. Last but not least, while broadcasters who use HD video downlinks for live broadcasting can offer extremely good results in terms of mitigating mutlipath interference, it should be borne in mind that the hardware and software they use cannot be compared to what would be practical in a hobby scenario. This is something I explained in an earlier posting as well. The MPEG2 or H.264 codec they use is often tailored specifically for the situation to which is put to use, and the processing power to implement such codec’s successfully keeping in mind the latencies they achieve, involves processing requirements from both a hardware as well as software (i.e. DSP – digital signal processing) point of view that would simply not be practical in hobby situations – from either or both cost/power/hardware size, volume or weight perspectives.

In short: no, complete mitigation for multipath caused interferences is not practical, and I don’t believe you can demonstrate a comparable alternative for the conditions we are talking about here, OMM(?).

I could probably quite accurately quantify in terms of overall interference what one is likely to experience from multipath type interference and it’s safe to say that that interference would overall be an insignificant interference (i.e. you wouldn’t be bothered by it and certainly wouldn’t be dissuaded from wanting to use HD video), but to say it can be completely mitigated – nope, that’s unrealistic given the obvious conditions & limitations that apply. Nuff’ said on that – I don’t think I can explain it or qualify it any clearer. If you can demonstrate (not just claim) any better, I’d like to know exactly what & how – it could be helpful.

Lets deal with another of the points you have raised – I’ll do my best to keep it short, but at the same time I am not going to makes performance claims or statements one way or the other without taking the trouble to put them into their proper context so that readers understand what I have said and why I make the claim.

Let’s deal with your 60millisec – 70millisec latency requirement. Like everything else you have made a comparison to, I guess this too is related to the latency figure that AMP claim (?).

Let’s put the AMP latency figure into its correct context. Actually, it ties in a bit with the previous point (multipath!!), but that aside for the time been, the 60 – 70millisec latency figure provide by AMP is first and foremost for an SD video stream – and on top of that, is given for a rather generous bandwidth of 2,5Mhz.

Give me a codec that offers HD streaming on a 2,5Mhz path while retaining picture quality consistent with HD transmission – and I will take up your 60-70millisec challenge – and that’s forgetting that HD horizontal res can be as much as close on 300% larger than the 704 pixel horizontal res AMP allows for its SD video content.

Horizontal HD res is around 1080 (for a 16:9 aspect ratio picture) – actually, immaterial of weather the comparison is with AMP, or any other manufacturers product for that matter, the principal still applies i.e. the 60millisec – 70millisec requirement you have introduced was a comparison with a video standard that requires substantially less bandwidth as well as bit rate/data content than HD Video would require. Its like comparing Apples with Oranges. It doesn’t make sense.

If that is not the comparison you are making (i.e. with AMP), then it would be great if you could explain where/how you derive this latency figure, and feel it should apply to HD video in this situation? I can’t see how, but perhaps I have overlooked something.

It’s one thing to make the claim or say this or that is required – it’s another thing to qualify that claim. And that too I explained a long time ago in an earlier note. I stated that I felt something around 120 - 180millisecs (or around 1/10 to 1/5 of a second was required). So quite why you now want 60millisecs – 70millisecs, despite me having made it clear what I thought was possible, is a little beyond me, but anyway …..

The relationship that latency has with multipath that I referred to earlier?

It’s about the DSP requirement - I am not sure it’s technically possible. I think I could satisfy 120 – 180millisec’s latency for multi-path error rates that would be insignificant in terms of overall time (to use a measurement folk can relate to), but to be able to realize complete mitigation of multipath interference free video in a 60millisec – 70millisec timeframe from rf hardware on flying model, bearing in mind the practical limits that would be imposed in terms of processing power, the practical hardware size, and the capability of the H.264 codec that would be available for a hobby flyer to use – nope. I can’t see how it would be realizable. I can’t see a complete situation (a situation that takes all the reliavnt points into consideration) that will offer such low latency and freedom from multipath interference. Easy to claim such, easy to say that’s what I want – it’s another thing been able to do it or explain how it can be done. I’ve explained why I don’t belive its practical – can you explain why you feel it should be achievable?

120milliseconds or 1/10 of a sec may not be good enough for you but putting aside the technical merits of either latency figure, both are reasonable latencies for command/control scenarios. Sure, I can highlight situations in which the difference could have an impact on an outcome, but by the same token most FPV flyers can factor in the difference between 60-70millisecs or 120millisecs/1/10sec and I don’t see many folk declining an opportunity to use kit with HD resolution because latency is 1/10sec and not 60millisecs (?).

I’m sorry OMM, it’s not my forum style to challenge people just for its own sake, but I am fast coming to the conclusion you have tried to challenge what I have written from the start, but really haven’t offered much in the way of explanation. As I said earlier, it’s easy to say this that or the other, it’s a different matter qualifying the statement and little of what you have said have you been able to qualify. I have to tell you that I have serious doubts with your claims regards 25year experience with spread spectrum, as much of what I have taken the trouble to put into context regards what you want such a system to satisfy in terms of performance, you should know is not practical for the scenario described.

It’s late, I’m off to get some shut eye now. I will reply to your requirement for “3x to 5x transmission distance for the same power tomorrow” – and will take the trouble to explain in a way that all can relate to just why it’s a ridiculous claim to expect a COFDM modulated signal carrying H.264 encoded content over 5Mhz – 6Mhz bandwidth, to cover the same distance/range/radius/ area coverage (or however you wish to put it) using no more “power” than an analogue modulated system of half the above bandwidth would use, or a system of equal bandwidth but less than half the data content or bit rate would use.

There are a whole bunch of additional issues when it comes to “power” and transmission distance. SNR has to be considered, CNR has to be considered. These spec’s change for different bandwidths, and modulation types. There are also changes in peak and rms power between analogue transmissions and digital transmissions for different bandwidths. If bandwidths and frequencies are the same, there will be differences in power requirements and power transmitted. When data density and/or bit rate changes power levels for SD video versus HD video will change.

There are so many different way of looking at this subject, I can’t think where to start, suffice to say that wanting 3 x to 5 x transmission distance for HD video transmission versus an SD video transmission, but to stipulate no more power than the SD video transmission would need or use, is ……. well, I’ll explain later. It doesn’t make sense.

Old Man Mike - you have sought to challenge me all through these notes, but in doing so I have to tell you the points you raise demonstrate your own somewhat limited understanding of the issues involved – and certainly not a knowledge level consistent with someone who has 25years of experience with spread spectrum. I am sorry I find myself saying this – it is not my style to challenge folk, or capitalize wherever I can to show someone up. I’m too old for that, and I confine my contributions to subject matter I understand and explain to others in terms they can benefit from. It surprises me that you feel you can take stance you have and challenge what I stated in the absence of been able to back your statements with any credibility.

Edited by Helix1

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Well, I confess to growing a bit tired of this thread. I will leave it with an apology:

Instead of "complete mitigation of mulitpath", I should not have made it so easy. I should have said:

"Use of multipath to ENHANCE overall S/N"

Your long standing friend knows very little about what can be done today, especially in the area of military communications. It is particularly amusing to see you say it is impossible to mitigate multipath when there are existing systems that already use multipath to enhance the S/N. As for not seeing any significant multipath in R/C flying, you obviously have never flown in non line of sight conditions which is most often the case for quadcopter flying.

Since this thread has evolved into something a bit tense, I'm bowing out. There appears to be nothing to be gained from my participation in it.

OMM

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Helix1, considering many online forums, this is a refreshingly practical one for people who make real things and try them out. Your big brother/best mate/esteemed colleague/whoever may well be bigger/brighter/right more often than Old Man Mike's, but - a word to the wise - a line about something you've built and tried out in the field is invariably of much more interest to this forum than multi-page lecture notes.

And please note that no-one is the least bit interested in how credible you, or Old Man Mike, or anyone else is. We just want to know what you're up to and what does and doesn't work, so we don't have to waste our time repeating experiments done elsewhere.

Register as a member, crack on and build this doohickey, and let us know how you get on - we're all very interested in that!

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I must say this thread has been very interesting but we have got to the point where we are arguing over details of a system that dose not exist. The only way to move forward is to build it!

I for one would be interested to see it done and very impressed with whoever manages it no matter what the details.

I tend to just go off and build stuff and not share them on here as much as some would like (Thomas tells me off for not posting details of my gadgets). The reason I do that is that there is always someone that will argue that I am doing it wrong or it will never work and I just cant be bothered to waste time trying to explain again and again why I am doing the way I am or that it already dose work.

Lets be positive and share what we can from each other without the need to turn it into a competition, I’m sure more info would be free flowing that way which is good for us all ;)

Terry

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The only way to move forward is to build it!

Yes, build it, even if it is just for yourself. In case you haven't noticed, just about every cool FPV product on the market today has its roots from a personal project that essentially grew into something that others begged to buy. For sure, many of us want a higher quality video link, so get to it. :)

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Well I am going to come in at the deep end here. This thread never started with anyone committing themselves to build anything for anyone, least of all Patrick. As I read it Patrick offered a very detailed and in my opinion excellent reply to an OPs question, It just so happened, like everything else Patrick said that he backed his statements up with detailed explinations. I joined this thread because I have a need for high def video from a high altitude balloom oddly enough. Patricks information was an excellent piece on very important points about the parts of hardware needed for high def video. After cross referencing what he wrote with other sources I find no fault with his comments. Certain members DID try their luck with him and wrote some rubbish or made statements or claims that dont stand up to scrutiny.

Terry is right, information would be far more free flowing if people adopted a positive attitude.

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After cross referencing what he wrote with other sources I find no fault with his comments. Certain members DID try their luck with him and wrote some rubbish or made statements or claims that dont stand up to scrutiny.

I've been following this thread as well because I've been interested in HD wireless video transmission for a while. But I must admit, much of what's in this thread is beyond the scope of my knowledge base.

You cross-referenced all of that information? Could you provide some links? You must have had a pretty robust knowledge base before you even looked at this thread. Most of this thread was, to me, like a fly buzzing in my ear.

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I've been following this thread as well because I've been interested in HD wireless video transmission for a while. But I must admit, much of what's in this thread is beyond the scope of my knowledge base.

You cross-referenced all of that information? Could you provide some links? You must have had a pretty robust knowledge base before you even looked at this thread. Most of this thread was, to me, like a fly buzzing in my ear.

Hannibal

Could you be a little more specific regards what you'd like some more info on - quite happy to help if I can.

Patrick

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