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tvi

Aug 23rd 2013, 17:43

WD9DMM

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
My neighbor just told me that she can hear my cw on her tv.My antenna is a vertical 29ft.Zero 5.My radio is a Icom 718 running 90 watts .She .does not have cable.Her tv is a flat screen model
My antenna is 25 ft away from her roof mounted old fashioned
antenna.All suggestions will be welcome.Many thanks
Matt Furlong. wd9dmm
Aug 23rd 2013, 19:58

W1MG

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Matt,

If the problem occurs even when the TV is off, and just the audio is affected, you may have a problem with audio rectification. If this is the case, removing the coax from the TV may not affect the interference. Although this problem is covered in more depth on page 19.9 of the 3rd edition ARRL RFI Book, here are some things that you can try…

First, you don't say anything about the speakers. If they are external to the TV, an easy thing to try is moving the speakers and bundling the wires. Or, if they are internal speakers, you could try disconnecting the wires altogether and plug in a set of headphones. If you notice an improvement, I would suspect audio rectification. It’s a relatively common problem. The RF is being picked up on the speaker wires and being conducted into the TV amplifier. (The output transistors rectify the RF into audio. The amplifier's internal negative feedback circuitry can also conduct it back to the high-gain stages of the amplifier.)

The stock cure for this problem is a common mode choke. The RFI Book has a detailed explanation, but building one is a pretty simple matter. Assuming that you are operating at HF, wrap ten to fifteen turns of speaker wire onto an FT-140-31 ferrite core. You can also use an FT-240-31 core if the speaker wires are large. The chokes should be installed right at the amplifier.

Note: If you can’t get toroid cores with type 31 ferrite, try using type 43. Simply substitute the 43 for the 31 in the core number.

Good luck and hope this helps.

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