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Old Feb 29, 2012, 08:47 PM
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Help!
Help finding the source for video interference

Hi.
I have ZII flying wing with 1500mw 1.2GHz with RV Filter (1500LPS) on one wing and DL RX in the other wing. RVOSD5 in the middle, TBS69cam and GOPRO.

I have seprate FOXTECHFPV 3A step-down regulator that feeds the vTX, Turnigy 3AMP BEC for servos and Turnigy 60AMP ESC with red wire disconnected. No seperate video battery, just 2 main 4S lipos.

I have ferrite ring on ESC data and ground wire, and also one on all 4 wires that gets into the vTX, near the vTX.

I have 12ch digital silver vRX. Also have Lawmate vRX that I didn't try yet.


I have 2 big white stripes interference in the video, as can be seen in the following sample.
I use Antenna tracker with 8 DBI patch so no reception problems should accour for miles, and ad can be seen in the video - I see the problem even in very close range.

Can anyone recognize the source and advise how to eliminate those interferenses ?

Test - Cont..ASF (15 min 1 sec)


Thanks ahead for helping,
Sharon
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Old Feb 29, 2012, 08:53 PM
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What control system? If it's 433Mhz UHF, its 3rd order harmonic may be spewing noise into your
video Rx.

ian
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Old Feb 29, 2012, 09:28 PM
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It is.
How far should I stand with the UHF TX from the antenna to make sure it is not it ?
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Old Feb 29, 2012, 09:32 PM
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Just keep moving further away and see if the noise is reduced. If it's the same
at 1m and 4m, then it's probably not UHF system. If it gets better, then you need at a minimum
a low pass filter installed on the UHF Tx.

[edit]I just realized you did mention DL Rx in first post. DL Tx should not create interference like that,
unless it's a very old system.

ian
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Old Feb 29, 2012, 09:47 PM
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If you are using the el Cheapo Rx's, any UHF system will cause some RF noise in the video.

however, that doesn't look like UHF noise to me...? most of the time it's just a noise blankout
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Old Feb 29, 2012, 10:03 PM
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80% sure that it's switching noise from your power supply.

Going out on a limb, that noise is conducted, not radiated. If the frame rate is 30FPS, and you're getting 3 bars a frame, the noise is somewhere around 100Hz. Since all our radios go way faster than that, its not RF. The only thing that I can think of that goes 100Hz is your PSU.

The PSU doesn't actually switch at 100Hz, but if its underloaded, it might cause low frequency noise

To test, plug a 3s into your system. If the noise goes away, then that means its your PSU's fault
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Old Feb 29, 2012, 11:12 PM
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Most switching noise I've seen results in much narrower banding, often somewhat diagonal, and
covering most of the screen. Also switching noise is usually constant magnitude even when the
plane is sitting on the ground close to the Tx. His comes and goes in strength, which indicates Rf noise
competing with the video signal strength.

One thing I can't help but notice is how loud and high pitched the audio is. I'd suggest
grounding the audio channel for a flight (just connect signal wire to ground wire) just to
rule out out. Sometimes overdriven audio can step on the video signal.

ian
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Old Feb 29, 2012, 11:18 PM
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possible overdriven audio + RF picked up from the 1.5watt transmitter aswell?
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Old Feb 29, 2012, 11:24 PM
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Quote:
Originally Posted by Daemon View Post
Most switching noise I've seen results in much narrower banding, often somewhat diagonal, and
covering most of the screen. Also switching noise is usually constant magnitude even when the
plane is sitting on the ground close to the Tx. His comes and goes in strength, which indicates Rf noise
competing with the video signal strength.

One thing I can't help but notice is how loud and high pitched the audio is. I'd suggest
grounding the audio channel for a flight (just connect signal wire to ground wire) just to
rule out out. Sometimes overdriven audio can step on the video signal.

ian
Hi Deamon.
The audio sounds like that becuse of the DVR, If I connect the vRX directly to sLCD audio input, I hear the modem beeps at normal level.
Thanks for your opinion.
Sharon.
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Old Mar 01, 2012, 12:03 AM
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Ian, we are talking about different types of PSU noise.

You are talking about switching noise, which is very consistent, and is generally above 50kHz.

I am talking about a different type of noise, which only results from a poorly designed underloaded power supply.

I'll do my best to explain....
The PSU has a minimum amount of power it can generate. If this is the case, the output voltage will ramp up because of the excess power, until the controller senses that the output voltage is too high, and it shuts off until the voltage goes back down. The controller senses that the voltage has fallen back to acceptably low levels, and the converter starts up again. This makes low frequency voltage ripple.

When I experienced this on my PSU, it was around 3kHz, but they could also be significantly slower, depending on the load. Since the load is not constant, the speed of these oscillations changes, and they sometimes might go away completely.

I might just be rambling, but its worth a shot. All you have to do is plug in a fully charge 3s and see if the noise goes away.
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Old Mar 01, 2012, 12:13 AM
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Whatever type of noise you're talking about should look pretty much
the same regardless of strength of video signal (proximity of plane to vid Rx) or
strength of UHF control signal's harmonics (proximity of UHF Tx to vid Rx), etc..
If you can power up the plane and video system on the bench, and see that same noise
then maybe it's something like that. I doubt it though. I've never seen any type of
noise from a power supply that looked even vaguely like that.

ian
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Old Mar 01, 2012, 03:49 AM
OSUFPV - KF7VFT
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Quote:
Originally Posted by Daemon View Post
What control system? If it's 433Mhz UHF, its 3rd order harmonic may be spewing noise into your
video Rx.

ian
+1 for this. My DL spews onto my 1.3ghz if I'm within 2m of the VRx. And
that's with a new filtered DL and a CP 8 lobe pinwheel antenna on the VRx.
But, if I stand 3m away I'll never see any interference. Try holding your DL
Tx right next to or near your VRx antenna and see if the banding gets worse,
then test far away. I bet you'll see a big difference.

Also I couldn't help but notice that your low pass filter was for 2.4ghz,
hopefully thats a mis-link because if you're using UHF its not doing anything
to help you.

Blues
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Old Mar 01, 2012, 04:24 AM
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Quote:
Originally Posted by Blueshy View Post
+1 for this. My DL spews onto my 1.3ghz if I'm within 2m of the VRx. And
that's with a new filtered DL and a CP 8 lobe pinwheel antenna on the VRx.
But, if I stand 3m away I'll never see any interference. Try holding your DL
Tx right next to or near your VRx antenna and see if the banding gets worse,
then test far away. I bet you'll see a big difference.

Also I couldn't help but notice that your low pass filter was for 2.4ghz,
hopefully thats a mis-link because if you're using UHF its not doing anything
to help you.

Blues
Thanks, I will try that and report back. I know now that the filter is useless but can it lower the range substationaly ? how much % should I expect ?
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Old Mar 01, 2012, 08:41 AM
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Quote:
Originally Posted by Daemon View Post
Whatever type of noise you're talking about should look pretty much
the same regardless of strength of video signal (proximity of plane to vid Rx) or
strength of UHF control signal's harmonics (proximity of UHF Tx to vid Rx), etc..
If you can power up the plane and video system on the bench, and see that same noise
then maybe it's something like that. I doubt it though. I've never seen any type of
noise from a power supply that looked even vaguely like that.

ian
You're correct. You would get this noise on bench tests. That makes it a lot easier to test.....
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Old Mar 01, 2012, 01:24 PM
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Inside the room there are no noise, but if I am very close to the vRX with DL TX the image dissapears completely - that does not seem similar to the noises I saw in the air.
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