ARRL

W1MG

Joined: Sat, Apr 4th 1998, 00:00 Roles: N/A Moderates: General discussion about technology and policy

Latest Topics

Topic Created Posts Views Last Activity
T8 Lamps Sep 20th 2011, 14:56 5 2,859 on 5/9/13
Part 15 and Plasma Televisions Sep 14th 2011, 15:13 2 1,191 on 14/9/11
Common-Mode Interference from Cable System Sep 13th 2011, 15:13 3 1,490 on 25/8/13
RFI from HVAC Systems Sep 1st 2011, 19:08 2 1,171 on 1/9/11
RFI from Plasma TV Sep 1st 2011, 17:20 3 2,763 on 13/9/11
Alignment of Vintage Shortwave Receiver - Pilot T-511 Aug 3rd 2011, 13:43 7 2,343 on 5/2/13

Latest Posts

Topic Author Posted On
tvi WD9DMM on 23/8/13
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.
GE X13 AC Air Handler Motor AF4RK on 1/8/13
GE developed the ECM (Electronically Commutated Motor) a number of years ago. It is a brushless high efficiency dc motor now being manufactured by the Regal-Beloit Corporation. They are now being rebranded by the Genteq Company, a division of Regal-Beloit.

For a variety of reasons, they now commonly used in HVAC systems. They can also be a source of RFI to nearby radio receivers. This document published by Regal Beloit also provides information on how to suppress RFI from an ECM motor:
http://p1k.arrl.org/~mgruber/ECM_Motor_RFI_Reduction.pdf
Grid Tie Pv INVERTER RFI concern K7YDL on 18/1/13
A friend has an SMA inverter and it's proven to be remarkably quiet. I forget the model number, but he has had no issues with it.
LED lamps and interferance n1naz on 30/5/12
From what I've seen so far, there can be a wide range of conducted emissions from LED bulbs, depending on model and manufacturer. I plan on testing a number of them in the near future.
30 meters QRN; 20, 40 quiet? K2ADK on 23/5/12
If the noise rolls off dramatically with frequency, one possibility might be a local RFI source. Walking around your neighborhood with a battery powered shortwave receiver might verify this possibility. Antenna resonances can also cause noise to peak at some frequencies.

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