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Mr.RC-Cam

Low Cost Digital Video is Finally Here!

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{Ok, low cost digital video is here, but not quite ready for FPV.}

I've been patiently waiting for the off-shore suppliers to begin releasing affordable digital (frequency hopping) video systems. I got my hands on a prototype and thought I would report on it. There's good news and bad news.

The one I checked out has a small video Tx (1.6 x 1.6 inch) that is rated at 2.4Ghz/50mW (higher RF power is being promised). Just like our digital R/C links, there is a setup step where you bind the Tx to the Rx. This is done with an on-screen menu.

The receiver has composite video output that can be set for PAL or NTSC. It also has a LCD hardware interface for directly connecting an LCD color display (this would be ideal for integration into video goggles). There's also a keyboard for selecting up to four different transmitters that have been paired to the receiver using the binding process.

Where it falls short is the frame rate. I haven't had time to figure out why, but my effective frame rate seems to be about 5fps. It was advertised at 11fps for 640x480 and 25fps for 320x240. When I have time I will play around with the settings to see if I can achieve that.

This product was designed for the security market where frame rate is not critical. The important thing in all this is that it will surely lead to something more appropriate for FPV applications. As soon as we see something with 800x600 resolution and low latency 20fps I think FPV will be able to move up from the analog RF systems. I will admit that will be a tough nut to crack!

Here is the Tx/Rx prototypes shown next to popular 900MHz/500mW Tx (for size comparisons).

post-2-12548464548_thumb.jpg

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wow that really is promising!! very cool.

640x480 at 15fps woudld be quite excellent... 25fpv would be amazing!!!

good find, keep us posted!

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Cool, shows theat there are signs of things going in the right direction :)

However, I wouldn't go for anything under 640x480/25fps. Anything below just ends giving you headaches...

What about encoding quality, range, latency?

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Encoding quality is fine, but certainly not DVD :) . Latency is about 100-200mS (my best guess based on listening to the audio echos), which needs to be greatly reduced for model aircraft FPV applications. Range is not bad for 50mW and the nice thing is that multipathing and signal nulls are completely masked. But of course frame updates can't happen during these events, but even so it is very cool that the video remains intact during the short signal losses.

Here are three video samples that will help demonstrate the mpeg compression and general image quality. Yes, the framerate is not usable for model aircraft FPV, but I can certainly see how it would be fine as-is for a slow moving R/C robot or common surveillance application.

Demo 1: Indoor images, shows the sluggish frame rate during camera pans.

http://vimeo.com/6937009

Demo 2: Close up images, shows resolution and compression artifacts.

http://vimeo.com/6937060

Demo 3: Range test. Video Rx is in building, mobile video Tx travels outdoors about 150 ft. There is an on-screen RSSI feature which shows signal strength, so keep an eye on it.

http://vimeo.com/6937271

I also checked the video Rx's immunity to a Spektrum 2.4GHz R/C transmitter. Not a single bit of trouble. Frame rate did not drop, so data collisions did not occur. I didn't check the Spektrum Rx's immunity to the video Tx, but I don't expect it would bother it. Overall, this technology is very promising. We are almost there!

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Pretty decent indeed! However I've only been able to watch the first video, the other 2 are set as private.

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I looked at the frequency hopping behavior on a network analyzer. What I saw was a bit unexpected; The system is suppose to use 2400 to 2483 MHz. But for some reason I see that it uses 2740 to 2840 MHz. I'm not sure why.

The frequency hopping is a round-robin affair. That is, it increments the RF at 9MHz (approx) spacing. There are 11 hops.

The Tx is factory rated at 50mW. The RF power was measured at about -45dBm, which is 0.03mW! I think this unusually low power level demonstrates one of the tricks behind spread spectrum -- it fools common measurement tools into thinking less power is being used.

The photo below shows the hops. They might appear to be present all at once, but that is just because the network analyzer is in storage mode (so you can see their spacing). In real-time you would see jumps to each RF spectrum location.

post-2-125493728581_thumb.jpg

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Interesting.

Personally, when looking at spread spectrum devices on my SA I've found that storage mode is best indeed, I'd leave the thing on for 1-2mins before looking, but what I would see subsequently would match the rated power...

The range test is interesting too. Firstly it seems the image really stops refreshing at 2 steps. Plus, while moving and during the time the indicator is full, the difference in refresh rate seems linked to image movement, like if the encoder just didn't have enough power to handle large differences between frames... or it's just a coincidence and the fast pans match RF "dips"...

How was that recorded? standard AV recorder on the output, or does the RX have integrated digital storage?

For reference, when you say "low cost", in what range would such a thing be?

I'm still interested in tackling the subject myself, and somewhat passively looking at the evolution in small embedded processing boards that would have enough power for video encoding/decoding, integrated wireless capabilities and all that in a small physical size... from what I've recently seen there have apparently been a few very interesting things coming out during this year, so we never know, if I can find some time during the winter that would make a good opportunity for me to get some experience in "higher level" embedded things - OS-loaded ones.

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while moving and during the time the indicator is full, the difference in refresh rate seems linked to image movement, like if the encoder just didn't have enough power to handle large differences between frames... or it's just a coincidence and the fast pans match RF "dips".

I think it is a combination of both issues.

How was that recorded? standard AV recorder on the output, or does the RX have integrated digital storage?

The receiver was connected to a PC in the lab that had a capture card. Not the best location for ensuring a reliable RF signal, especially since the exterior masonry walls have metal wire mesh in them.

One of the things that would be cool is to have the digital TX include an onboard memory stick for video recording. That way you get wireless video for FPV and onboard recording for publishing higher quality videos. Maybe one day.

For reference, when you say "low cost", in what range would such a thing be?

Expect a street price of $150 to $200 for the Tx/Rx pair. A little bit more for one with a built-in LCD display on the Rx.

I'm still interested in tackling the subject myself, and somewhat passively looking at the evolution in small embedded processing boards that would have enough power for video encoding/decoding, integrated wireless capabilities and all that in a small physical size.

I'll be at the CES show next year to seek out new wireless video technologies. Hopefully some useful new designs are available for live demos.

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If the picture dose not refresh for a couple of seconds you may not even know you have crashed !

Terry

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If the picture dose not refresh for a couple of seconds you may not even know you have crashed !

I kind of like that. :)

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One of the things that would be cool is to have the digital TX include an onboard memory stick for video recording. That way you get wireless video for FPV and onboard recording for publishing higher quality videos. Maybe one day.

Definitely, that's on my "mandatory" list should I work on that.

Expect a street price of $150 to $200 for the Tx/Rx pair. A little bit more for one with a built-in LCD display on the Rx.

Now that is VERY cheap indeed. But frankly I'd rather give 5 times that for something that is actually useable... :unsure:

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Now that is VERY cheap indeed. But frankly I'd rather give 5 times that for something that is actually useable...

I expect it will indeed cost 5X for something that works well for us. But to its credit, this low cost system is usable, just not for real time aerial FPV. :)

What we need will come in due time. We just need to hang on a bit longer.

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