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Old Jul 27, 2014, 01:04 PM
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Interference with UHF 433 and video 2.4GHz... Why?

It's quite wierd, but this morning I had interferences with my UHF and video receiver (specs below). On the plane, the distance between the VTx and the Rx is about 45cm and on the ground the Tx was almost 3m away from the VRx.
When the plane was farther than 50m I totally lost video.... I tried this video Rx Tx at 1Km and no interference and no problem at all, but instead of using the DTF UHF of 1W I was using an orange opnelrs of 100mW. So I guessed it was a matter of harmonics of the 433, but the frequencies are quite far to have this problem...
I was about to buy a low pass filter, but reading this thread I have serious doubts that the cause is the harmonics: IBcrazy - post #4 - the uhf radio simply swamps the video signal regardless of harmonics
So, what do you think? any idea? Thanks!


Specs:

- Video Boscam 2.4G 8CH 500mW Wireless Transmitter Receiver TS321+RC302
- Radio TX DTF UHF 1Watt (first version, the one with the plastic case)


Manu
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Old Jul 27, 2014, 05:20 PM
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Joined Oct 2011
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Quote:
Originally Posted by M_3one View Post
It's quite wierd, but this morning I had interferences with my UHF and video receiver (specs below). On the plane, the distance between the VTx and the Rx is about 45cm and on the ground the Tx was almost 3m away from the VRx.
When the plane was farther than 50m I totally lost video.... I tried this video Rx Tx at 1Km and no interference and no problem at all, but instead of using the DTF UHF of 1W I was using an orange opnelrs of 100mW. So I guessed it was a matter of harmonics of the 433, but the frequencies are quite far to have this problem...
I was about to buy a low pass filter, but reading this thread I have serious doubts that the cause is the harmonics: IBcrazy - post #4 - the uhf radio simply swamps the video signal regardless of harmonics
So, what do you think? any idea? Thanks!


Specs:

- Video Boscam 2.4G 8CH 500mW Wireless Transmitter Receiver TS321+RC302
- Radio TX DTF UHF 1Watt (first version, the one with the plastic case)


Manu
It's not so much about harmonics, infact I have looked at the OrangeTX on a specrtum analyzer and it's pretty clean on the 3rd harmonic (1.2GHz), but instead overwhelming the front-end of the video RX.

An RX can get overwhelmed by any frequency if the filtering is bad, or shielding is bad, etc. For me I found ferrites on the video inputs to the RX, the power, and a filter on the antenna, as well as carefully sealing both the RX and UHF TX in metal tape that is grounded gave me OK results. I was able to go about 3 miles with a pair of fans / SPWs, and did 6 miles with a crosshair, though I turned not because of video but battery (Note my video is 1.2GHz).
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Old Jul 28, 2014, 02:30 AM
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Quote:
Originally Posted by NorCalMatCat View Post
It's not so much about harmonics, infact I have looked at the OrangeTX on a specrtum analyzer and it's pretty clean on the 3rd harmonic (1.2GHz), but instead overwhelming the front-end of the video RX.

An RX can get overwhelmed by any frequency if the filtering is bad, or shielding is bad, etc. For me I found ferrites on the video inputs to the RX, the power, and a filter on the antenna, as well as carefully sealing both the RX and UHF TX in metal tape that is grounded gave me OK results. I was able to go about 3 miles with a pair of fans / SPWs, and did 6 miles with a crosshair, though I turned not because of video but battery (Note my video is 1.2GHz).
Yes, I think you're right, it's not a harmonic problem but somehow the Tx overwhelms the VRx. So what you did:

- Ferrites to the power and video inputs of the VRx and a filter on the antenna (a high pass filter?)
- To seal with metal tape VRx and Tx. I think this will create I kind of a Faraday cage. I have copper tape, so I'll try it, but I have some doubts about how to put it. If you have any picture it could help me.

Thank you very much for your answer!

Manuel
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Old Jul 28, 2014, 12:02 PM
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Yes a high pass filter, it will help to heavily attenuate the unwanted 433 by the time it gets through the filter and help to keep it from overwhelming the vRX front end.

Copper tape would be great, yes it is a Faraday cage you would be making, just make sure the entire thing is well wrapped with it, when I did mine I wrapped it fully only leaving small openings for the LED's and button on the TX. Make sure the copper tape makes good electrical contact to the SMA connector so it has good ground connection.
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Old Aug 03, 2014, 12:27 PM
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Hi NorCalMatCat,

I just tried the Faraday cage and nothing has changed I also tried the Faraday cage on the radio Tx with same results... The only thing that seems to help is to reduce the power of the Tx. I started with 3 over 7 and I couldn't go farther than 100m without losing video. With 1 over 7 seems to be better, but I have to try it on field, and I don't know how much the radio range will be reduced.....

Anyway, I just bought the RMRC filter for 433, I think that is my last option.
If anyone has any idea, please let me know!

Thank you all!!
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Old Aug 17, 2014, 06:53 AM
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With the low pass filter nothing has changed... still having interferences
I'll have to buy another video receiver with better filtering, but I'd like to know the reason. Any suggestion for a good video receiver?
Thanks
Manuel
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Old Yesterday, 01:17 AM
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Today I have achived a little improvement. I changed the antenna on the vRx (instead of the skewplanar I used the stock antenna - whip) and I could go more than 400m away, but no more
I've uploaded a video with the interferences. The video has two flights, in the first I used the skewplanar on the vRx and in the second the whip antenna. Note that in the second video I was flying with a multicopter instead of the wing, but the setup is the same (the video transmitter is the same), and previously I tried with the skewplanar on the vRx and I couldn't go farther than 100m.
I know there are many expert people here and I hope you can help me

Thanks,

interference (1 min 9 sec)


Thanks,
Manuel
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Old Yesterday, 02:41 AM
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That doesn't look like harmonics from a UHF system to me.
There's a lot of other things on 2.4Ghz band. Could be something like
wifi or bluetooth on your phone or someone near you.
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Old Yesterday, 03:12 AM
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I've tried in 3 different locations, so its something related with my equipment or my mobile... I'm going to switch off my mobile and see what happens, but I don't think this is the problem.... Could it be multipath?
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Old Yesterday, 03:14 AM
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It's not multipathing.
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Old Yesterday, 03:55 PM
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This morning I did some tests and I recorded them in a video. All the tests were done with a RMRC low pass filter for the Tx and with the phones switched off. It was quite windy and I didn't fly, so I put the plane 50m far from the ground station. First I show that the problem comes from the Tx. When I switch on/off the interferences appear/disappear.
In the following tests I change the antennas of the Tx and vRx. The best performance is with a whip antenna in the vRx, but still having interferences

Tests (2 min 20 sec)


I've tried everything, I did many tests and I've read this forum quite a lot to find an answer, but still having this issue. I donīt know what else to do.
As a summary, these are all the thing that I did without any improvement:
- Different antennas on vRx y Tx
- Removing the case of the vRx
- Putting copper tape on the vRx
- Putting copper tape on the Tx
- Putting copper tape on the bottom of the Diamond RH-771 antenna. This solution really kill the interferences, but reduced the radio range to 150m

I thing it is related with the Tx and vRx antennas at a frequency of 433MHz (because of the low pass filter)but I'm not an expert. I hope someone can help.
Thanks,
Manuel
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Old Yesterday, 06:13 PM
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Only thing left is to try a high pass filter on the VRX. I know many people
who fly 433Mhz UHF control + 2.4Ghz video without issue, so can only conclude
that it's a problem with that particular VRX picking up the primary UHF signal,
not a harmonic.
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Old Today, 12:12 PM
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If Daemon's suggestion (high pass filter) does not solve the problem then I have a couple recommendations based on what I saw in your video.

1. I see excessive cable lengths on the vRx. To help investigate common mode RFI noise issues, retest with extremely short power and video cables on EVERYTHING connected to the vRx. Do not attempt to use long cables until after the problem is solved. Do not share vRx power with anything and keep the power cable short.

2. If short cables provide some improvement then the EMI/RFI issue appears to be too excessive for your snap-on clamp filters (their split construction reduces performance). Replace them with toroidal type with *A LOT* of cable wraps. All cables to the vRx (and sometimes the R/C Tx) should be protected with Toroids. Install the Toroids close to the entry points to the equipment. In some cases it is necessary to stack several Toroids together to achieve sufficient RF attenuation, like this:
https://encrypted-tbn3.gstatic.com/i...F-1lgNjfp738QA


Since you want to know more about what is going on you will have to keep kicking rocks until you find what you are looking for. Nasty EMI/RFI issues are often due to a combination of several things and so success can be frustrating to achieve. Especially if the vRx's design has poor protection from your UHF signal. Good luck.

- Thomas
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Old Today, 12:38 PM
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One thing I find about EMI introduced through the cables is that it's usually not
nearly as distance dependent, if at all. In other words, when my 433Mhz UHF Tx is
putting noise directly into my goggles or DVR through the A/V cable, it looks the same
at 1m as it at 20km. His noise is distinctly distance dependent, video is
perfectly clear up to a point and then noise hits pretty suddenly. My guess is that the
front end of the VRX is poorly filtered, and as the receiver's automatic gain increases past
a certain point, it allows the 433Mhz signal to swamp it completely.
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Old Today, 02:18 PM
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I agree; That's why I recommended the additional steps after the trying the high pass filter. If the high pass does not fully solve it then there is some common mode EMI/RFI that is introduced into the system via the cables.

Assuming the vRx cooperates, I think that it will require efforts on both the RF input and the cables to get reasonable results. So filter the antenna ports and expect to filter the cables.

- Thomas
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