[sdiy] Preventing Radio Ham Interference

Tim Ressel timr at circuitabbey.com
Mon Nov 28 20:03:50 CET 2016

That can help. The mesh size needs to be significantly smaller than the 
signal wavelength. In this case we're talking 2 meters, so a quarter 
wave is half a meter. Chicken wire is small enough that it should work. 
It would not work for something like radar or microwave ovens (yes, they 
do leak) where the wavelength is about 30mm or less.


On 11/28/2016 10:55 AM, random variate 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 <mailto:weplar at gmail.com>
> Sent: ‎28/‎11/‎2016 18:28
> To: Oakley Sound <mailto:oakleylist at btinternet.com>
> Cc: Synth DIY <mailto: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 <http://www.oakleysound.com>
> >
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--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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