Jump to content
Mr.RC-Cam

Analog HD FPV Video. Why Not?

Recommended Posts

Lately there's been a lot of interest in high definition video for FPV piloting. Especially for drone racing. Who wouldn't want a true widescreen display with real HD resolution? The good news is that several different HD FPV systems have recently appeared. These range from the DiY WiFiBroadcast project to ready-to-use products such as Connex Prosight. There are others too.

But these new systems are digital implementations. And the ugly warts from data compression, latency, and weak RF signal behavior are bothersome to some of us. Enough so that I expect it will turn off a lot of potential users that will simply keep flying with their existing analog FPV system.

I'm here to open up a discussion about doing it a different way. Instead of digital, why not HD analog video? It's possible; The technology is similar to our existing CVBS (NTSC/PAL) video devices and video processing chip sets are readily available. It just needs someone to dig in and develop a package specific for FPV. I would like to light some fire and offer inspiration to tackle the challenge!

So let's talk about it.

 

Share this post


Link to post
Share on other sites

What is Analog HD? It is a video camera technology that was developed for the CCTV industry. That should have a familiar ring to it, since our current wireless video systems have their roots in that same market.

There are several different competing Analog HD systems. All are essentially composite video on steroids. The two most promising for our FPV application are AHD and HD-TVI. Both are analog, uncompressed, and without latency! Plus they use progressive video, so no interlacing artifacts.

Here's a summary of the popular analog HD technologies that are used in hard-wired CCTV installations:

AHD.jpg
Note: AHD now supports 1080p, but is missing from the chart.

Here's a YouTube video that compares a 1080p AHD camera to a HD-TVI camera:

 

And here's a video that compares a very high performance analog 960H CCTV camera to a 720p AHD:


Analog 700 TVL versus HD-TVI 720p

 

Edited by Mr.RC-Cam
Added HD-TVI video

Share this post


Link to post
Share on other sites

Unfortunately it seems that useful technical information is not openly published on the internet. I haven't bothered to start a relationship with a silicon vendor so I can get some data sheets. An easier workaround was to buy a AHD camera and investigated the video signal with my o-scope.

The camera I reviewed is a SamSung 1080p AHD. The most striking thing is that the AHD's video waveform has the look and feel of our existing FPV video. The video levels are similar (~1Vpp) and familiar landmarks such as colorburst, Vsync, and Hsync, are all there. I like it already!

But the AHD's wide view and high resolution requires more video bandwidth. Instead of the 5MHz we currently use, the 1080P AHD camera needs about 25MHz. Applying that to the FPV 5.8GHz raceband allocations, this would limit us to 3 pilots in the air at once. However, I expect that the 720P cameras will reduce the bandwidth considerably and allow 4 pilots. But I have not confirmed this. Sure wish I had some data sheets!

I found that the 1080p AHD video uses ~24MHz color synchronization (instead of the NTSC's 3.58MHz colorburst). VSync is only 30Hz (instead of NTSC's existing 60Hz interlaced rate), but still provides 30Hz frame refresh. HSync is about 33KHz (twice our current 15.7KHz). The faster HSync is used to eliminate interlaced video.

Interesting information was gained in the measurements. I learned that 1080p is not a first choice due to the high bandwidth it requires. However, high definition 720p looks great and would be a noticeable upgrade to our existing FPV image quality. But I don't have a 720p AHD camera to measure. A 720p HD-TVI camera should be checked too. It's impossible to make a decision on which is the best choice for an analog HD FPV solution without knowing all the little details.
 



test.jpg

Even with the insufficient bandwidth that's available on our existing analog FPV systems, I was curious if I could get an AHD camera to work with it. So naturally I connected the 1080p AHD camera to a FatShark 5.8GHz 250mW vTx. The video out on my ImmersionRC 5.8GHz vRx was connected to a AHD compatible surveillance DVR (with VGA monitor). I didn't expect any image at all, so it was a real treat to see the camera's image appear. It was missing color and the image resolution was slightly less than my usual FPV image, but it worked!

So a crude proof of concept step has been done. Now do I have your attention?

Share this post


Link to post
Share on other sites

This is not expected to be a simple DiY project. Each FPV component (camera, vTx, vRx) needs to be modified a bit. But its not as difficult as creating a digital video system from scratch.

Here's some things to consider.

1. This analog RF technology will require a ham radio license if used in the USA (and many other countries). This is the same restriction imposed on our current analog FPV systems, so it's nothing new.

2. An unmodified CCTV DVR could be used for ground station recording. It would also convert the video to HDMI for connecting HD goggles and monitors. But it would be nice to have something that was designed specifically for FPV (small size, dual HDMI video outputs, SD Card, low voltage alarm, etc.).

3. The large RF bandwidth would limit practical use to the 5.8GHz RF band. Fortunately 5.8GHz is the video system frequency used by most "drone" pilots.

4. The RF modules in our existing vTx and vRx will need to be modified. They currently are limited to about 5MHz video bandwidth. This would need to be increased to about 15MHz (my estimated guess for 720p video). I could be wrong, but I don't believe the Richwave chips found in most 5.8GHz modules are capable of doing this as-is. But maybe there is a workaround that can use the standard chip, otherwise a custom solution might be needed.

5. Assuming we'll need 15MHz video bandwidth for 720p, receiver sensitivity will be reduced about -4dB (compared to 5MHz bandwidth).

6. The existing AHD and HD-TVI cameras are large, so a smaller form factor is needed. Also they all seem to use CMOS sensors instead of CCD. But keep in mind that the digital HD video systems are also using CMOS sensors.

7. None of the existing OSD's will be compatible. So for video telemetry a new OSD is needed. This feature could be built into the camera rather than as a separate module. The OSD's communication interface will need to be open source and support the same functionality found in the popular minimOSD.

8. Audio could be supported by adding a compatible sub-carrier to the analog RF modules. This would increase the occupied RF bandwidth. Ideally the end-user should be able to disable the sub-carrier if audio is not required.

Share this post


Link to post
Share on other sites

That about wraps up my thoughts on analog HD for FPV. Perhaps no one has similar feelings about it as I do. Maybe I've missed something that makes it a dead end idea for our FPV application. But I think that the general concept deserves consideration. Maybe someone will agree, get inspired, and make it happen. :)

Share this post


Link to post
Share on other sites

As a hobby level project I think it is the way to go but I think mainstream HD is going to happen anyway and will come from one of the big companies when it does. I also think they will want to side step the band width problems by going digital even if this means a little latency. I guess what I am saying is that the hobbies speed of progress has outstripped the DIYers for the most part. There is still room for the talented DIYer to do some fun stuff as you proof again and again but HD FPV in my opinion is not time well spent, its coming anyway.

 

Terry

Share this post


Link to post
Share on other sites

Mainstream digital FPV has begun for sure. Connex is available to purchase and other systems are following:
http://www.hobbyking.com/hobbyking/store/__104213__CONNEX_8482_ProSight_HD_Vision_Pack_for_FPV_EU_Version.html

BTW, you can get a good sense of it's performance in this big Connex discussion:
http://www.rcgroups.com/forums/showthread.php?t=2661113

But not every FPV'er is convinced that digital HD will be the ultimate holy grail. However, on paper the analog HD solution sounds like a better fit for FPV (and should solve the digital HD issues).

Along with the expected performance advantages, analog HD's simpler technology will always be lower cost than digital HD. But that has a market disadvantage; Because the technology is non-proprietary, I doubt a western developer will touch it (because investors like proprietary / closed systems so they can own the market). But its open architecture is suitable for the Chinese engineering/manufacturing culture.

I'm hoping that like-minded FPV developers see the potential of analog HD. Especially since it is a cheap & available technology that seems to have been completely overlooked for our application. So that's the reason I've started a conversation about it.

Share this post


Link to post
Share on other sites

I see where you are coming from, I remember a discussion about HD a few years back. If I remember correctly it was the bandwidth that was the main issue then?

Years back I did sketch out a system to use 2 side by side standard systems similar to some of the computer screen surround gaming screen set ups now. The main difference was that by using prisms I could lose the bar where the 2 screens joined to make an almost perfect picture. I didn't pursue the idea very far as at the time I was mainly interested in using the camera feed to aim my stills camera for AP. The other problem that put me off taking it further was the inability to record in the wide format so it would only be any good for live viewing.

A proper HD system would be far better so I will be watching with interest!

 

Terry  

Share this post


Link to post
Share on other sites

Yes indeed, we talked about the bandwidth bottleneck a couple years ago. Back then I was hedging my bets that digital (WiFi) solutions would come along and save the day. Now that they are here we're finding that the good comes with some bad. At this point the larger bandwidth requirements of an HD analog solution don't seem so nasty after all.

 

Share this post


Link to post
Share on other sites

I've been searching for a source to a 720p compatible AHD or HD-TVI wireless link. At this point I don't care how big it is. The goal is to do some basic "field" testing, especially to check the video behavior during weak signal conditions.

This one says it is 720p/1080p AHD:
http://www.globalsources.com/gsol/I/CCTV-receiver/p/sm/1125303588.htm#1125303588
I have some doubts that this one is really HD compatible. Some other sites that list it show specs that suggest it only provides standard composite video.
EDIT/UPDATE: The supplier confirmed it is not actually AHD compatible. So another dead end.

This one has a small vTx and says it is 720p/1080p compatible. But no mention if it is AHD or HD-TVI:
http://sectronics.manufacturer.globalsources.com/si/6008848564400/pdtl/CCTV-receiver/1130260635/5.8GHz-8CH-AV-Transmitter-Receiver.htm
EDIT: It is NOT 720p/1080p compatible. The giveaway is that the audio subcarrier is at 5.5MHz. So skip this one!

I cannot find any sources to a wireless AHD or HD-TVI compatible vTx / vRx. This ends any chance of a practical analog HD field test. At least for now.

 

Edited by Mr.RC-Cam
Update: No AHD vTx / vRx sources can be found.

Share this post


Link to post
Share on other sites

I purchased a 720p AHD CMOS security camera and checked the video signal on a o-scope. As hoped, the required bandwidth is not horrible. For example, the color synchronization (color burst) is half of 1020p AHD (about 11MHz).

So my optimistic prediction was spot on; That is to say, for 720p HD video we just need to find an analog RF link that supports about 15MHz of video bandwidth. Without schematics it will be too difficult to modify existing vTx & VRx designs to support it. Unfortunately I have not found any commercially produced AHD wireless link solutions. So further testing of the analog HD FPV idea is on hold for now.

But overall it seems that the concept of analog HD FPV would be practical. Plus the low-tech requirements would be cheap for a China factory to produce (probably the same cost as the bargain priced SD FPV systems we currently have).

Share this post


Link to post
Share on other sites

This TX + RX looks small enough to be used on drones, now we need either RX with HDMI out and low latency or AHD compatible screen which could be used in FPV goggles.

http://www.airwave.com.tw/en/2-2851-113400/product/Wireless-AHD-RF-Module-AHD-Module-id512161.html

http://www.airwave.com.tw/en/2-2851-113400/product/Wireless-AHD-RF-Module-AHD-Module-id511732.html

Edited by Walkeer

Share this post


Link to post
Share on other sites

Thanks for the links. Looks like Airwave has modified some existing A/V modules to support AHD. I see that audio is not supported on them. The stated ~4MHz video bandwidth is goofy, hopefully its just a typo. The vTx RF power is 25mW and vRx sensitivity is only -85dBm like their other 5.8GHz modules.

Is there any interest in experimenting with the Airwave AHD modules? I can use my existing relationship with Airwave to place a group-buy order. Anyone that wants to do that then please post your interest in this thread.

BTW, a group-buy is the same thing we did many years ago when rc-cam members were experimenting with 5.8GHz video (back when all those naysayers said 5.8GHz would be useless for FPV).  Those efforts helped introduce 5.8GHz video systems to the hobby. Now it's time to play with AHD and perhaps start another FPV revolution! :)

 

Share this post


Link to post
Share on other sites

I can imagine that wireless transmission of AHD itself will not be a big problem, however problem might be to display it on some LCD with low latency. I have searched LCD with AHD support and found only some lowres test screens on aliexpress, not suitable for this purpose. Either AHD LCD driver will be needed, or AHD to HDMI convertor, but both must be low latency.

 

Camera should not be a problem, there are couple of cheap and small 720p: 

https://www.dhgate.com/store/product/mini-ahd-camera-3-6mm-lens-720p-1-0megapixel/390720511.html

CCD: https://www.aliexpress.com/store/product/Mini-AHD-camera-mini-720P-1-0megapixel-CCTV-Camera-security-camera-indoor-AHD-mini-camera-ahd/716987_32487143507.html 

Edited by Walkeer

Share this post


Link to post
Share on other sites

That is correct, the AHD's FM modulation would not add to latency. And as you have noted, the point where latency would be introduced would be at the display. I suggest starting with a randomly chosen AHD to HDMI convertor (about $50 USD) to get things going; At some point someone will find a compatible LCD or HDMI convertor with low/acceptable latency.

Regardless, latency issues (and solutions) will not be known until the community starts experimenting with DiY AHD FPV systems.  And latency is a secondary issue, the FPV video quality must be remarkably better too. 

I'm interested in AHD for FPV, but I can't do it alone. If anyone is working on it then please share your project details.

Share this post


Link to post
Share on other sites
Quote

AHD wireless link exists, ...

The internal photo I found shows they use Airwave's 5.8GHz patch antenna.

big_av-300_struktura.png?lm=1505856458

Plus on their Polish web site the advertised channel frequencies and RF power match Airwave's AHD vTx module:
http://ewimar.pl/pl/system-bezprzewodowej-transmisji-video-300m-av-300-mini.html

But on their english site the RF specs (Freq list and power) are different:
https://shopdelta.eu/wireless-transmission-kit-ahd-m-5-8-ghz-av-300ahd-mini-txrx-set_l2_p9235.html

All this research is interesting, but who is going to get the ball rolling and build/buy a AHD based FPV system?

 

Share this post


Link to post
Share on other sites

It appears that a community driven AHD FPV project is not going to happen. So to get the ball rolling I plan to do it myself using Airwave AHD1.0 compatible modules.

BTW, to add to the research findings I came across another interesting Taiwan based AHD module supplier called Go-Link.
http://www.go-link.com.tw/index.html

Go-Link offers 720P and 1080P 5.8GHz AHD video modules that could be candidates for FPV. However, 1080P's vRx RF sensitivity is only  -70dBm due to the massive required bandwidth, versus the 720P's higher -80dBm sensitivity. Also, their 720P module supports four ham-legal RF channels whereas there are only two available for 1080P.  Because of these limitations the 720P modules would be the better choice for FPV.

 

Share this post


Link to post
Share on other sites

For the receiving/displaying end you could use ICs from Analog and NexChip, NVP6124/NVP6114A for video RX and conversion to Digital 8bit ITU-R BT.656 and then ADV7511 for Transmitting the HDMI signal to goggles/monitor. I think it could be all packaged into one nice RX station/box with VRX and HDMI out.

Links to ICs:

Quote

 

Share this post


Link to post
Share on other sites

Thanks for posting the data sheets. They might help someone with their AHD project.

For me, a component level build is too ambitious. Instead, I'm going to create an experimental DiY AHD FPV system using "off the shelf" parts. I already have a 720P AHD board camera. The  Airwave AHD vTx/vRx modules and a AHD-HDMI video adapter should be in my hands in a couple weeks.

However, I have some other projects to finish before I can start building the AHD FPV system. So it will be delayed several weeks before there's any progress to report. In the meantime, maybe someone else will chime-in and tell us about their DiY AHD FPV project.

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×