[sdiy] Preventing Radio Ham Interference

[Barry Klein]

One idea I’m wondering about that I haven’t read of doing before – get/make/borrow a RF dummy load and replace the antenna with it.
If you still get interference it is a coax and/or grounding issue.

Barry


From: Rick Jansen 
Sent: Monday, November 28, 2016 11:21 AM
To: Tim Ressel 
Cc: synth-diy at synth-diy.org 
Subject: Re: [sdiy] Preventing Radio Ham Interference

OTOH, 20 watts RF power is a *lot* of power. You can expect you neighbour to not direct that at your house.

rick

On 28 Nov 2016, at 20:03, Tim Ressel <timr at circuitabbey.com> wrote:


  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. 


  --tr




  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
    Sent: ‎28/‎11/‎2016 18:28
    To: Oakley Sound
    Cc: Synth DIY
    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 mailto: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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    > Synth-diy at synth-diy.org
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--Tim Ressel
Circuit Abbey
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