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Gary Evans

1160MHz video interference

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Thomas could I get your opinion on the possible cause of this interference. It occurs unless the plane is close and directly in front of the ground station.

Fox 800mW Tx on 1160MHz with 1.3 dipole antenna

Twin Lawmate Rx's on patch antennas with a diversity

I have flown a differant plane at this site with the same model video Tx/ground station and the reception was perfect.

http://www.youtube.com/watch?v=K3B7_HZK_Iw

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The interference appears to be from a digitally modulated RF source. Given how strong it is, it may be something you brought with you.

Don't shrug off stuff that you've brought along in the past. Sometimes these RF issues suddenly appear from things that used to be friendly but have decided to no longer play nice. First on the list would be to re-check your R/C Tx to see if causes the noise. Then investigate everything else that was with you at the time of the problem. Even the electronic gadgets that are not intended RF radiators.

Or it could be a RF signal from a source in the surrounding area from something new, or is normally turned off but in use on the day you flew. I won't give you any lectures about using 1160MHz. No doubt you fully understand the intended purpose of that RF frequency band, which is not open to amatuer radio users. So be mindful that the interference pattern could be from a legitimate source that might not be amused by FPV.

The other forum members will probably have some advice too. It might help to list more details about your FPV setup in case they need it to help diagnose the issue.

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Thanks Thomas. 1280MHz will be the first thing to try. Onboard equipment includes-

Fox 800mW 1.3 Tx with 1.3 dipole

Scherrer 433 Tx/Rx

RVOSD

THERMAL SCOTT audio varimeter (wingedshadow.com)

E-Flite 25BL motor and Phoenix ICE 50 ESC

Castle 10amp BES

Maxx Products electric spoilers

tinyurl.com/6wfnsuu

Edited by Gary Evans

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I have flown a differant plane at this site with the same model video Tx/ground station and the reception was perfect.

Was that with the Scherrer UHF system too?

Some 1.3GHz receivers don't appreciate the proximity of strong UHF TXs.

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Was that with the Scherrer UHF system too?

Some 1.3GHz receivers don't appreciate the proximity of strong UHF TXs.

Yes it was. I did originally have a problem between those two but changing from Fox to Lawmate Rx's solved it. Apparently the Fox digital Rx isn't filtered very well.

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Flew today on 1280MHz video and the interference was much less although there are still bursts of white horizontal bars as shown in this uncut clip. More importantly note at 9:50 I tried manually switching between patch antennas and one signal was extremely bad.

http://www.youtube.com/watch?v=PkLkUvhi-YA

Back on the bench in trying to duplicate this behavor I notice that both leds are flashing constantly at a high rate. My spotter said they were doing that in flight. I tried differant sensitivity settings and anything above #1 produced the same result. I could still manually switch between antennas but after a few seconds both leds would constantly flash at a high rate. This was with the video Tx about 20 feet away from the Rx. Is this normal?

http://www.youtube.com/watch?v=1BbQl0dr2CA[/media]

Edited by Gary Evans

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Flew today on 1280MHz video and the interference was much less although there are still bursts of white horizontal bars as shown in this uncut clip.

I don't see any of the digital modulation interference on your latest video. So moving to 1280MHz seemed to be a good thing for that day's flight.

I notice that both leds are flashing constantly at a high rate.

This is usually due to video levels that are incorrect (which causes Oracle to constantly switch Rx's while it searches for valid video). So you should check your video levels with the o-scope (white level must be industry standard 1Vpkpk).

Keep in mind that not all suppliers ensure the video equipment is properly calibrated. And video levels will usually be wrong if you mix Tx and Rx brands. Also, on some wireless A/V systems, moving from one RF channel to another will also cause the video levels to change dramatically. So when you calibrate your Tx's video level, do so using the intended RF channel.

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Keep in mind that not all suppliers ensure the video equipment is properly calibrated. And video levels will usually be wrong if you mix Tx and Rx brands. Also, on some wireless A/V systems, moving from one RF channel to another will also cause the video levels to change dramatically. So when you calibrate your Tx's video level, do so using the intended RF channel.

I'll add that OSD's can sometimes mess this up quite a bit, I've had the same problem of an Oracle switching continuously that only happened when the OSD was in line. It was jsut driving black/white a bit too aggressively and messing up sync detection.

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I'll add that OSD's can sometimes mess this up quite a bit

Yes, some of the early OSD's used graphics with unexpected video levels and it caused a severe Video SAG issue on some wireless links. The video sag confused Oracle since it messed with the syncs. Fortunately I haven't seen this issue in awhile, but it is something to keep in mind. BTW, the sag issue is a worse hardship when it is combined with incorrect video levels from the video Tx/Rx.

So to play it safe, my recommendation is to use your o-scope and calibrate the wireless video levels with the OSD removed. Verify that the Oracle is working correctly (only one LED on at a time). Then install the OSD, recheck the video levels, and verify correct Oracle operation. If the OSD causes the problem to re-appear then use its menu controls (if available) to adjust the OSD's graphic video levels. And as a side benefit, carefully calibrated video levels should provide the best video quality (won't cure the RF problems, but your monitor, DVR, and eyes will be happier).

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Follow up.

Not having a scope as suggested to check the video level I resorted to swapping parts.

First thing was to try another Fox 1.3 Tx with no improvement.

Next a Lawmate 1.3 Tx same result.

I then bypassed the RVOSD and the diversity receiver resumed normal operation.

Lastly I then tried a different camera (201), which worked with the OSD connected.

Sooo what this means is that the 480 camera originally installed was not compatible with the RVOSD and Diversity receiver. It would produce a good picture only it the diversity receiver was bypassed. I do not have another 480 camera to try but suspect that the problem may be just this camera since I have used it successfully with the same equipment in the past.

I flew with the 201 camera yesterday and everything worked fine. Still getting some interference on 1.28 at 12 second intervals. Maybe a beacon at a nearby airport?

Edited by Gary Evans

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Sooo what this means is that the 480 camera originally installed was not compatible with the RVOSD and Diversity receiver. {snip} I flew with the 201 camera yesterday and everything worked fine.

If the different camera cured the Oracle's rapid switching then it sounds like a video level issue. So there is reason to believe you can fix it up. That is to say, if you want to use the 480 camera then hunt down someone with an o-scope and calibrate the Tx's video level.

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