Solving Stereo / Home Theater Radio Frequency Interference caused by Ham Radio

Having suffered DX withdrawal, I decided it was time to put up a new antenna.  The antenna in question was a Icom AH-4 Tuned Dipole of about 36M length in total, about 9M high at the apex.  Whilst I realize it is far from optimal in many ways, I was interested to see how it would perform on the higher bands, and thought it might significantly improve my local contacts on 40M & 80M.

It seems to have delivered on 80M, my local Winlink Winmor speeds on 80M have gone from 100 Bytes / Minute to a huge 1100 Bytes / minute, and I’m once again hearing the local farmer’s nets!

However, there is much testing to do, and the story today is about the problem the new antenna caused!  I like to play on JT65 at night, when there isn’t much going on, and I’ve setup my radio so I can do so remotely via my laptop.  Whilst relaxing in bed playing JT65 on 20M, I decided it would be a good idea to listen to some music, but my new antenna thought otherwise!

My home stereo system is pretty basic but nice.  It consists of an Audio Engine DAC (usb sound card), and a Miniwatt N3 3.5 Watt Tetrode Amp.  A good friend of mine, Peter VK3OJ, had recently given me some old (but working) 12AU7 tubes, and I was keen to see how they sound compared to some of the newer models.  However, the moment I transmitted on 20M, the left speaker would buzz, and the computer dropped the soundcard!

At first, I decided to tackle the buzzing speaker.  I added some chinese (ebay sourced) snap on ferrite cores one by one and transmitted, until the buzz died down.  It took 12 snap on cores to achieve a decent result, however this didn’t stop the computer from dropping the soundcard.

I then put 4 snap on cores on the USB lead, but that didn’t help.  I added another 4, and hey presto! I could now listen to music and DX!

The moral of the story is that the age old solution to RFI of snap on cores works, even with cheap ebay sourced chinese cores!

If you’re like me and enjoy listening to music while using digital modes, or have a neighbour who has issues with RFI on his sound system, you couldn’t do better than buying a bunch of snap on cores on ebay.  Many Chinese sellers will sell them in bulk (shop about, put ’10’ in your search etc), and I was certainly glad to have these ones in the shack!


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