2.4gHz video cutting out

[daniel reese]

Using a small (tiny) 2.4ghz tx with a composit video and telemetry data overlay transmitted to a small rx and recorded directly to a laptop.

The video breaks up at much over 30-50' separation. I had thought it was vibration but even when carrying it by hand it has the same problems. Ive tried using as large a DC current as the devices are rated for and still the problem persists.

Am now considering some db gain patch antennas. Anyone have any experience similar to this and find a solution?

Here's a sample of the video problems
http://video.google.com/videoplay?docid=3984668152020998056&q=telemetry&total=199&start=30&num=10&so=0&type=search&plindex=9

[Hogster]

What transmitter and receiver antennas are you using? Also what's the rated power of the transmitter (should say on it ... or at least it should say what it is in any documentation that came with it)?


David :)

[MLaBoyteaux]

What's the power rating on the transmiter?

I solved my dropout problem by going with a 1 watt transmitter.

[daniel reese]

There wasnt any documentation in the box with it (yeah, surprised me too) and there isnt any power rating noted anywhere on either the tx or rx but Im fairly certain its in the low miliwatt range.

The tx is about the size of a book of matches, twice as thick with a short thick antenna. The rx is one of those typical 2.4g 4channel jobs- just a bit bigger than a deck of cards- same antenna. Both powered by 9-12v.
Got it from RVMShop.com (through ebay- the $60 one with the seperate tx,rx & camera. Yeah, i know ya get what ya pay fer but I really did expect range just a bit higher.
Luckily, I hope, the antennas are seperate gizmos and Ive seen the same tx & rx on other sites coupled with patch antennas that proclaim much improved range and clarity...

Looking for someone with some experience doing just that. Im not into serious AP, Its just nice to have a video downlink so i can see what my helicopter is looking at. The ACT Labs blackbox telemetry overlay is pretty handy too (Alt., Airspeed, RPM, video supply voltage & heli rx supply voltage)

If this setup is say, just a few miliwatts, would patch antennas help?

[Hogster]

You can either go up in power (cheating really ;)) or take a more careful look at your RF system .... I used to use a 600mW transmitter, but in order to fall in line with the regulations in the UK regarding 2.4GHz wireless video transmission I changed down to 10mW. With careful thought about how I built the system (keeping all the RF cables as short as possible, the number of intermediate connectors as low as possible, and the transmitter and receiver as close as possible to their respective antennas), I can get plenty of range from it .... more than enough for my application of HeliAP ... :)

Can you post some photos of your setup? Both of the transmission and reception sides of the system ....


David :)

Edit: Just seen your next post :) Yes patch antennas will definitely help. I use an 8dBi one on my system which is about the size of a CD, but square .... you can see a photo of my whole system here (http://www.hogster.rchomepage.com/logo10/heliap_setup_2-8-07_large.jpg).

[daniel reese]

I'll post some good pics tonight- work servo wont let me access Photobucket, Youtube, Google or Yahoo....frustrating sometimes...
By way of verbal description, the Camera video output goes through about 8" of av cable to the Blackbox where it gets the telemetry overlay, from there out through adapted lipo balance leads- 3" - to the tx which has the stubby antenna mounted on it. That antenna is pointed forward within the fuselage (TT MD500)

The rx has the same antenna mounted directly to it, which then sends the signal through a 24" av cord to my video capture device, from there to the laptop.

I thought the blackbox might be the problem but I tried bypassing that but there was no change. I was originally powering it with a 7.4v lipo, I bumped that to an 11.1v lipo with no change. I thought vibration might be a problem so I tried hand carrying it- no change. I tried having the tx(with its ant.) outside the heli; even all by itself without the heli alltogether...no change. This rig seems to have an effective range of about 50'
Transmitters with higher output wattage are seriously expensive and, frankly, just not worth it for what Im doing. If I can get a stable picture at aobut 300' by adding a pair of patch antennas (one to the heli, one to the groundstation) fer bout $100, Im all for it. As for dropping another $100 on a tx, another $100 on an rx, another $100 on antennas &ca &ca...aint worth it.

Anyway, I'll post some pictures when I get home.

Thanks for your help so far fellas!

[Tonystott]

I added an 8Db patch antenna to my cheapie eBay system and have no trouble getting a good download reception as high as we dare fly the Trex 450 (see pic taken from lower than we have flwn)

[daniel reese]

Here's the bird- TRex600 (electric) in a ThunderTiger MD530, converted to civilian MD500E
http://i129.photobucket.com/albums/p232/daniel_reese/T%20Rex/CIMG0666.jpg

Here's the camera Im using: RCA SmallWonder digital video (has good resolution despite the aparent heavy dust on the canopy...honestly, it aint THAT dirty all the time. Beyond the layers of filth you can see the av cable connected on the right, just below the USB download port.
http://i129.photobucket.com/albums/p232/daniel_reese/T%20Rex/HPIM1474.jpg

From there the video signal goes through a short cord to the ACT Labs Blackbox telemetry device where it gets a data overlay to the video. In this picture you can see the airspeed sensor hose going down to the pitot tube as well as the rpm sensor (red & black twisted wire). Not connected are the barometric altimeter hose, blackbox battery and helicopter rx battery. (While powered from its own 7.4v battery, it will monitor helicopter rx battery voltage and send that info to the groundstation as well)
http://i129.photobucket.com/albums/p232/daniel_reese/T%20Rex/HPIM1422.jpg

From there it goes forward to the wireless tx placed just inside the window glazing (this picture is from the rear, looking forward out the nose. Thats the tx in the lower right. After this picture was taken, I respliced that cord eliminating the cumbersome RCA jack. The connection is now direct from the camera to the blackbox, and from there to the tx.
http://i129.photobucket.com/albums/p232/daniel_reese/T%20Rex/HPIM1465.jpg


Here's the groundstation stowed
http://i129.photobucket.com/albums/p232/daniel_reese/T%20Rex/HPIM1406.jpg

Deployed
http://i129.photobucket.com/albums/p232/daniel_reese/T%20Rex/HPIM1401.jpg

The 2.4gHz RX is secured to the open lid by two cap screws that aren't threaded all the way in. The antenna is completely above the lid. This setup is just a monitor (Insignia portable DVD player) When I want to record, I use my Gateway laptop in its place. All else is the same

Ive tested every permutation of connections on this and it would seem that the number of connectors or length of cable has not been a major cause of the problems, neither is te blackbox the cause since even by itself, it glitches beyond 50'. I suspect signal strength/clarity

Im hoping to have results like the last fella- by adding (in my case) a 8.5" patch antenna to the rx to eliminate the glitching

[daniel reese]

Looked up my wireless tx online- 200mw output power

[bullaculla]

200mw should get you past 50 feet. I'm using a 900mhz 500mw tx with normal antenna on the RX, and I flew my 600 high enough that I completely lost the tail but downlink was crystal clear. I know hte conditions are different, and I have over twice the power, but 200mw doesn't sound weak at all. I guess you just have to try a stronger TX. mine is about the same size as yours, but it gets hot! I had to put a heat sink on mine. I think the patch antenna is directional.

[daniel reese]

Mine gets VERY hot too. Looks like the heatsink from an Align ESC would do great- where do you find something like that?

If it aint the output wattage, what other options could I explore. Ive tried everything from long cables with lots of connectors to absolute minimum length cables with minimal connectors (one on each end) Ive tried eliminating all distractions leaving nothing but the camera and transmitter. Ive tried 2 different cameras (the one I have in place being the better of the two). Ive tried puting the tx and antenna outside the fuselage, tried pointing the ant straight up, straight down, even pointed at the rx. I thought vibration might be a problem so I tried hand carrying it away from the rx. Ive tried AC power, 11.1vdc, 9vdc & 7.4vdc. AC power caused its own faint waves in the image but there was no noticeable difference between any of the dc sources....Im running out of ideas other than to try either an 8 or 14db gain patch antenna on the rx.

[MLaBoyteaux]

What about using a better transmitter antenna like this one:
http://www.yb2normal.com/antenna3.html
It looks simple enough to build, I just need to find a piece of coax with the proper sma connector on it.

I've been using the standard dipole that came with my transmitters and an 8-db patch on the receiver. We keep the patch antenna tilted and pointed at the heli in flight, but with the 600mw transmitter, we often had drop outs or times where the signal would black out, especially when flying close to straight overhead, even when only at 100'.

I bought a 14db patch antenna, but it's MUCH larger than I anticipated, so I'm not using it at the moment.

I had to replace one of the transmitters we lost anyway, so I bought a 1000mw transmitter to try. It has tremendous range, but we're still experiencing spots where the signal will drop out momentarily.

[bullaculla]

The tips of the antenna are supposed to be the weakest part so if they are pointed right at each other it may cut out. On my heli, my little antenna is pointing straight out towards the back. No problems yet on 500mw.
Mark, how big is the 1W Tx? are you on 2.4ghz?

[jeffk]

I believe you would be better served by getting a better RECEIVE antenna.

Adding more transmit power MAY help, but your range should be better than it is with the system you've got, which tells me that there may be an inefficiency at the receiver. A better receive antenna will help in this area. In any good radio system, your receive antenna is as important, if not MORE important than your transmitter.

If it were me, I'd pick up a cantenna or a yagi-type antenna used for wireless networking. It's the same 2.4gHz frequency band, so it should work well. Hook that up to your receiver (you'll probably need to do some connector modification) and try it out.

Being directional though, it will need to be pointed at the heli at all times, so it might be a good idea to fly with a video helper.