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Author Topic: TVI via House Wiring?  (Read 5756 times)
NW9T
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« on: May 17, 2011, 09:39:46 PM »

It seems that when I operate on 20 meters is the only time the TVI appears, and it doesn't make a difference if I'm running 5 watts or 100 watts. 

What I've done:
Disconnected cable and peripherals to TV, interference was still present. 
Installed RS snap together ferrite choke to AC line going to TV, interference was cut by about 50% but still there.
Installed other ferrite choke, they come in pairs to AC line to rig's power supply, no change.
Disconnected power supply from rig and used Marine Battery for power, TVI virtually non-existent.

Neighbor, who's TV is less that 30 feet from my TV (our houses are very close) has no trace of TVI, so it sounds to me like it's entering the TV via the AC house wiring.  TV is connected to a surge protector strip which is SUPPOSE to have a filter built in, but seems to be ineffective in this case. 

RS also has the snap over type chokes that are sort of tubular in shape.   Would these be a better type to use and how many should be sufficient? 

Any suggestions would be appreciated. 
 
Especially from anyone that has experienced the same problem.

Tomorrow I'm going to try changing the lengths of power lines from power supply to rig and taking out the extension cord and using only cord on power supply as well as re-routing the coax if problem still persists.
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AE4RV
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« Reply #1 on: May 17, 2011, 09:48:04 PM »

You might try a Tripp Lite Isobar at the TV and maybe the rig. They filter noise as well as provide surge protection and tend to last much longer than cheap surge suppressors.
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K5LXP
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« Reply #2 on: May 18, 2011, 07:00:52 AM »

What's the antenna, and where is it in proximity to the affected equipment?  Could be coupling from the transceiver chassis to house ground via common mode.


Mark K5LXP
Albuquerque, NM
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AA4PB
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« Reply #3 on: May 18, 2011, 07:25:33 AM »

Since you say that there is no TVI when operating from battery (presumably into the same antenna) I would guess that the real issue is an unbalance in the antenna system that is causing the radio chassis to be "hot" with RF. When you connect to AC power then the RF is conducted along the house wiring (probably the ground conductor) to the TV.

If the antenna is fed with coax you may find that a choke (coil of coax) located near the entry point to the house will minimize RF on the radio chassis and fix the TVI issue. The actual solution here depends on what type of antenna you have and how it is fed (coax, open wire, tuner, etc).

In most cases it is better to fix the problem at the source rather than trying to filter it out of the TV set.
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NW9T
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« Reply #4 on: May 18, 2011, 07:57:02 AM »

As far as which antenna it makes no difference.  Currently I'm using the S9v 31' vertical which is approximately 50 feet from the TV, very small city lot.  I've used attic dipoles, outdoor wire antennas including dipole, long wire, D3, Carolina Windom, G5RV and 1/4 home brew vertical.  Same problem with all antennas and all on 20 meters only, no TVI on any other band from 2 to 80 meters including WARC bands.  I have used with and without coax coil choke no change.  I've used a Line Isolator and no difference. I've fed resonant antennas showing 1.1:1 or less with no tuner coax fed and no difference with or without choke/isolator installed. 

I was thinking maybe it was a shielding problem in the TV since it's only happening on 20, but with the TVI not showing up while battery powered that doesn't seem to be the issue. 

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NW9T
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« Reply #5 on: May 18, 2011, 02:39:37 PM »

Steps taken today:

Moved rig to furthest point in house away from TV, which is in far corner of basement away from the service box.
Power supply plugged into the most up-to-date outlet in house, tried both with and without surge suppressor.
All coax outside of house except for small length to rig through window, included coiled section to act as choke outside of radial pattern and just before window to basement.
Tried two rigs, the initial one which is Yaesu FT 895D and old Kenwood TS 120S.
Installed new ground with rig and tuner both grounded to it.

Results:

No change. 

Again nothing else in house seems to be affected just that one TV.  Three computers and none show any kind of interference. 

TV is older Zenith CRT type with analog tuner. 
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W3LK
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« Reply #6 on: May 18, 2011, 03:58:56 PM »


Again nothing else in house seems to be affected just that one TV.  Three computers and none show any kind of interference. 

TV is older Zenith CRT type with analog tuner. 

Geez, quit chasing your tail and replace that dinosaur. Problem Solved!!!
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NO2A
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« Reply #7 on: May 18, 2011, 04:25:56 PM »

Quite some time ago on one of these forums there was a lady having tvi problems with a ham in Co from a half mile away! It turned out the tv was an old Zenith from about 1966. The tv used a 7mhz i.f. frequency,so it actually was a receiver on 40m. Don`t know what i.f. yours uses,but chances are that`s the problem. I bet replacing it would solve your tvi problem. The ham in the other situation bought the lady a new tv and no more tvi reported.              Wink
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NW9T
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« Reply #8 on: May 18, 2011, 07:16:23 PM »

W3LK you're probably right, but I really hate to get rid of perfectly operating TV in every other respect. 

NO2A thanks for the information on the previous discussion.  Since this IS a TV with an analog receiver, and it's much newer than 1966, dating from just before the release of the big screen LCD TVs, but still older by today's standards.  The set is set to Channel 4 and channel switching is done by the box provided by the Cable Company.  I believe it's the 5th harmonic of 20 meters also lands within the channel 4 frequency range. I'll have to check the box, I haven't yet, to see if I can change it to channel 3 instead of 4 and see if that makes a difference. 

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K5LXP
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« Reply #9 on: May 20, 2011, 07:03:04 AM »

I think the fact that you could put a ferrite on the AC cord and there was an effect, plus a reduction when the transceiver is operating from a battery does imply the interference is coming in off of the AC line.  I would work the AC cord angle a bit more - if one ferrite helped, 2 might help more, and maybe four or eight might eliminate it.  You reach a point of diminishing return with that but you can hope for knocking it down enough before that diminished return point is reached.

Something not mentioned is the antenna source for this TV - is it cable, satellite, or broadcast?  I think it merits a bit of experimentation there to see if the TV is affected at all via its RF input.  Filtering out a 20M signal there would be a snap with a simple high pass filter.


Mark K5LXP
Albuquerque, NM
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NW9T
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« Reply #10 on: May 20, 2011, 07:34:44 PM »

It's cable.  I called the cable company to see if I could change the output of the box from channel 4 to channel 3, and it's a no-go.  According to them whether it goes into your TV on channel 3 or 4 depends on the area of the country serviced by your local office, and ours is 4 only.  Makes no sense to me, but that's what they said.

I ended up adding a second ferrite choke and according to the person watching the TV to check for differences between 1 and 2, when I keyed up the rig it actually made it worse.  I went back to 1 choke on the AC in to the power supply and also added a couple more to the DC Power lines between the power supply and rig, no change there either.

What I have found is if I keep it below 25 watts there's no problem.  So for the time being I can still get on the air on 20, but at reduced power.
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M0HCN
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« Reply #11 on: May 21, 2011, 01:22:23 PM »

What happens if you transmit  into a dummy load?

Try a ferrite on the cable TV cable and the cable box power cable.
I am thinking that the cable TV cable is normally earthed at the entry point and thus might form part of a RF earth path.

Incidentally it can be worth winding the mains lead through the ferrite a few turns, the inductance is proportional to the square of the number of turns.

Are there any other connections between the rig and ground apart from the power and aerial feeder? I am thinking links to computers or such which may provide an earth path that bypasses the ferrite.

A current mode choke in the aerial feeder is always worth trying in these situations and is not exactly complicated, see Jim Browns paper at http://www.audiosystemsgroup.com/RFI-Ham.pdf for more then you ever wanted to know.

Regards, Dan.
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NW9T
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« Reply #12 on: May 21, 2011, 06:54:09 PM »

As far as ferrite on the Cable input I'm not sure that would help since I had disconnected the cable/box etc. and the TVI was still present.  At that time the only connection to the TV was the AC Power.  I've tried the rig by itself with only the coax and power supply connected, no peripherals or computers, TVI still present.  The only time it's not present is when I hooked the rig up to a battery rather than through the power supply which is AC connected. 

I think RS was shocked I bought a package of their split ferrite cores, and figured maybe there's going to be a run on them.  I went back to the same store today and the price jumped almost $3.00 for a set of 2 compared to a couple of days ago.  From $5.98 to $8.94 for the exact same product.

I've been looking into the Tripp Isobar suggested by  AE4RV above and will check Monday to see if there's a local source available to pick one up, if not I'll send off for one as it's still cheaper than buying a new TV.  Wink
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KF7CG
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« Reply #13 on: May 21, 2011, 07:03:13 PM »

It almost sounds as if the TVI is generated by interacion between the rig and its power supply. Lets see the interference has to travel back down radio power leads into the supply and back out down the power lead to get into the TV. The heavy filtering should go first on the power supply ac supply and the secondly on the leads from the supply to the radio.

Heavy filtering between the radio and the supply might be just the thing to eliminate this because it will eliminate RF from the radio from getting into the supply.

It may well be coming as a varying load on the supply.

David
KF7CG
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W3LK
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« Reply #14 on: May 22, 2011, 06:03:30 PM »

The problem exists with only ONE consumer item, an old analog-based TV with a CRT. The whole problem can be solved by replacing the old TV.
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