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Author Topic: TVI on neighbor's DirectTV satellite receiver  (Read 2706 times)
K7JQ
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Posts: 333




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« on: October 06, 2005, 07:36:02 AM »

My neighbor is getting audio (not video) TVI on his DirectTV satellite receiver into his Toshiba big screen TV from my HF transceiver. We did some tests and it's on 20 meter SSB running about 500 watts pep...other bands seem clean. At 100 watts, no problem. No other TV's in HIS house (also on DirectTV) are affected. All the TV's in MY house are clean, and I'm using a Bencher YA-1 low pass filter on my radio. I noticed that the satellite receiver feeds his TV with an S-video output and left/right audio outputs to his TV aux input, not coax converting either channel 3 or 4. The two audio cables that the satellite company installed look thin and cheap..little or no sheilding. I'm thinking that the distance of my antenna to his TV is causing audio overload to his front end that could be enhanced by the cheap audio cables picking up RF (as an antenna) into his TV. Think high quality audio cables might be a fix? Any ideas would help. By the way, I moved my antenna further away from his house and the audio interference lessened in intensity, but not eliminated altogether (using a High Sierra screwdriver mounted on a steel fence in the back yard..CC&R restrictions). Thanks.  73, Bob, K7JQ  
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WB2WIK
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« Reply #1 on: October 06, 2005, 10:19:17 AM »

Moving the antenna up higher, so that it's not radiating in a line with the neighbor's equipment, would probably help even more.  "Low" antennas that are close to residences are the leading cause of RFI/TVI generated by hams.

You might try better shielded audio cables, that's certainly an easy one to test and even very good ones aren't expensive.  If the interference is common-mode, though (picked up by the shield), then better shielding usually doesn't help but "ferrite" does.  Wrap the audio leads through ferrite toroid cores (a few wraps will probably do it) at the entry point to the TV and see if that helps.  Again, a simple, cheap and easy test.

[RFI due to low antennas is so common, though.  Even when homes are well spread apart.  I was on 20m last week during a local windy day and my neighbor Mel W6FDR was on running low power, which he never does on 20 meters.  I asked "why," and Mel, who lives on a multi-acre property with no antenna restrictions, said, "Because of the winds, I have the tower cranked down.  If I run more power, I get into the alarm system with the beam this low."  Heh heh heh...it can happen to anybody.  Cranking the tower back up to normal height fixes it every time.  No substitute for "distance" when it comes to RFI mitigation.]

BTW, I have DirecTV/TiVo converters all over my home and running 1500W output on several bands I can't get into it at all; however I never tried a lower antenna.  My lowest HF beam is up more than 40' above the house even with the tower retracted for wind.  But this is still pretty good testimonial to the RF immunity of the DirecTV converters.

WB2WIK/6
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AA4PB
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« Reply #2 on: October 08, 2005, 04:39:54 PM »

Since it's not present in the video I doubt that front end overload is the problem. More likely the audio cables are picking up your RF and feeding it into the audio amp. Better shielding may help. Ferrite cores on the audio cables near the TV might help. Wind several turns of the cable around the cores. Radio Shack had some cores that would snap open to make the job easier.

The best way to troubleshoot something like this is to break his TV system down (divide and concur). Disconnect the various cables from the TV and re-connect them one at a time to find out how the RF is getting in.
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KG6AMW
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« Reply #3 on: October 10, 2005, 07:52:32 AM »

Don't forget about the VCR/DVD players if they are connected to the TV.  Sometimes they make dandy antennas.
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K7JQ
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« Reply #4 on: October 11, 2005, 01:49:20 PM »

Thanks everyone for your input. Used high quality, double shielded audio cables with two ferrite split beads on each.....problem solved!
73, Bob, K7JQ
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PY1BR
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« Reply #5 on: October 17, 2005, 11:54:19 AM »

I think my TVI problem is the worst I have ever heard about. I move to a small building in town (7 floors). I put a 40m band dipole and lot of TVI on Satellite dishes. Including mine. I use mine to test. I tried every kind of filter (coax over ferrite toroids, ferrite beads, AC line filters, etc. It’s unbelievable because my station doesn’t “do” TVI on an old TV antenna for common use of all apartments!!! No TVI at all when using the TV VHF/UHF broadcast antenna. And it’s not the best TV antenna we can buy.
All satellite dishes are recently installed, good coax cables and connections. I can’t understand why so many interference!! I did a test with AC power line: I plugged my whole TV system in a no-Break (APS) for computers without been connected to the wall (using batteries). Nothing changed. I know some hams that live in a quite similar situation and dipoles with many dishes and no TVI at all. Should I check my rigs? I have only Icom rigs (775DSP and 756Pro). All the neighbors that use satellite dishes are very angry with me, so I stopped transmitting from this QTH.
Please, if someone have ever had this kind of situation, let me know.
Best regards,
73 from EG, PY1BR
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KF7CG
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Posts: 832




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« Reply #6 on: October 17, 2005, 03:34:23 PM »

How are the dishes connected the receivers? Are they connected through the regular antena connection, the standard video connection, the S-video connection, or are they component video?

Each of these methods will have its own rfi weak points.

The standard video, S-video and component video use separate audio connections; do they have audio interference?

The rf input, tv antena, is generally on channel 3 or channel 4 and has the rfi susceptibilities of those channels and a susceptibility at frequencies up to 4 mhz on either side of the channel frequency.

It may be that the newest Direct TV receivers are lacking in selectivity and sheilding.

David
KF7CG

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PY1BR
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« Reply #7 on: October 18, 2005, 06:32:59 AM »

Hello all,
The satellite system I have is similar to the Star Choice provider using the Motorola DSR315 receiver. It's not DirectTV. I use component video connection, and the second one through channel 3 for a second TV set. There's no audio intereference. Only video. I have also a TV (VHF/UHF) antenna connected to the receiver. No TVI at all through the TV antenna. Image and audio just perfect. I still think that the RFI it's comming through the power line. Even after tested using the Back-Up power UPS (batteries). I still think that the RFI is harming the receiver. Also, the power line neutral I have it's not perfect. I measured 50 Volts. Probably this situation helps to increase RFI.
73
EG - PY1BR
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KF7CG
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Posts: 832




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« Reply #8 on: October 20, 2005, 06:45:17 PM »

I am not sure of your electrical distribution system. Here in the USA we would be all over the electrical company or the building owners to fix the electrical problem. 50 volts on the nuetral means that the system is very unbalanced. You may even have a break in the nuetral at or after the breaker box and this means that you could have some dangerous conditions occurring as appliance and lights are switched.
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K8MHZ
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Posts: 115




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« Reply #9 on: October 26, 2005, 06:52:18 AM »

RE: Neutral voltage

You should have NO voltage on the neutral when measured to ground as the neutral is a GROUNDED current carrying conductor.  There should only be current resulting from the imbalance of the two 'hot' legs of the system.

If you have a voltage reading at the neutral you have a high impedance ground and that is both dangerous and illegal in a residence.  You need quit playing radio and call an electrician before either someone gets hurt or the voltage on one side of your system gets so high that it damages sensitive equipment.  An un-grounded neutral can cause a feed to double in voltage under certain circumstances.

My recommendation is to call a Union electrician that specialized in troubleshooting (not running pipe Wink) and did good in school.  He won't cost you any more and should be able to find the un-bonded neutral quickly.

Stay safe and 73,

Mark K8MHZ
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