[sdiy] Preventing Radio Ham Interference

Sarah Thompson plodger at gmail.com
Mon Nov 28 20:11:47 CET 2016

Best advice is to reach out to the local ham community, which are typically
full of people who jump at the chance to fix that kind of thing. I'm a ham
myself, so I have experienced that flavour of nerdiness first-hand!

The #1 solution would be to put the antenna on a taller mast. For 2m, a few
more feet of elevation makes a large difference in terms of energy at
ground level. Forget trying a partial Faraday cage -- it might work
somewhat, but it's a lot of effort in comparison with getting the antenna

The other question is... why are they running so much power on 2m with a
beam antenna? You can pretty much get arbitrary line of sight with a 1/4
wave vertical on about 10 watts. 2m has relatively little knife-edge
propagation so it doesn't bend around structures well, so it's more or less
limited to line of sight. Their best option is to get the antenna higher,
which pushes the horizon out much further, and keeping the power down. It's
part of the FCC regs that hams shouldn't transmit using more power than is

Hope this helps,
Sarah NQ6K

On Mon, Nov 28, 2016 at 10:55 AM, random variate <
randomvariate at hotmail.co.uk> wrote:

> Could a faraday cage like wall of grounded chicken wire mesh help? (can
> you tell I'm not an EE?)
> Tim
> ------------------------------
> From: Tony K <weplar at gmail.com>
> Sent: ‎28/‎11/‎2016 18:28
> To: Oakley Sound <oakleylist at btinternet.com>
> Cc: Synth DIY <synth-diy at synth-diy.org>
> Subject: Re: [sdiy] Preventing Radio Ham Interference
> Funny this should come up now, I am reading my university textbook on
> analog filter design and the example I am studying is a ham operating at 30
> mhz ( impossible as it's out of band) causing interference to tv channel 2
> , the design calls for 20 db 4 pole high-pass filter. But that's for radio
> or tv reception.
> Speaking of interference, I will shut up now;)
> TK
> > On Nov 28, 2016, at 11:14 AM, Oakley Sound <oakleylist at btinternet.com>
> wrote:
> >
> > Hi all,
> >
> > My next door neighbour, a keen radio ham, has erected a new 144MHz
> directional beam antenna. Unfortunately, for both of us, when it's pointing
> towards my house and transmitting, it interferes with my audio set-up in
> both my living room and my little music area. I get on very well with my
> neighbour and we've briefly worked together on this so we know what
> particular combination of output power, frequency and antenna choice causes
> the problem. This antenna mast is around 5m away from the wall where my
> audio gear is situated. When he uses his other non directional antennas
> there is no problem.
> >
> > Anything more than 20W and the RF signal has an affect. Generally, with
> my more modern gear it is not a problem, but my vintage gear (eg. my hi-fi
> and older synths) are badly affected. More annoyingly, it's also the
> modular and my ten year old Event active monitors.
> >
> > When transmission is ongoing I hear what seems to be a loud buzz at
> 100Hz and harmonics. It's as if the mains is being gated into the audio
> pathway during transmission. The higher the RF output power the louder the
> buzz. The Event monitors pick up the noise even with the audio cables
> unplugged and the mains additionally filtered. Bizarrely it also makes the
> modular and my old SY-1 go out tune but I can't detect any drop in power
> supply voltage so I think it's directly affecting the VCO circuitry.
> >
> > I think I may have solved it with ferrites on the loudspeaker cables on
> the hi-fi but the music area is still a problem.
> >
> > At the other end of my house I haven't got an issue but moving all my
> gear there isn't really practical - although I'm thinking about it.
> >
> > Any ideas? Would some sort of earthed wire mesh fitted to the wall
> directly between him and me create a suitable RF shadow?
> >
> > Tony
> >
> > www.oakleysound.com
> >
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