[Elecraft] Computer Noise ruining 20 & 30m

[Bill W5WVO]

Great suggestion, Tony! A good way to tell if your RFI is being picked up by 
leaky coax in the shack or by your beam is to rotate the beam. If the noise 
changes amplitude during rotation, then at least some of it is being picked up 
by your antenna, and the only solution is to eliminate the noise at its 
source. This was the case in my situation, where my 6M stacked yagis are 
fairly close to the shack (about 35 ft), but far enough to one side that the 
directivity of the array had an effect.

Bill W5WVO


N2TK wrote:
> I have had good luck replacing RF noisy PC power supplies with PC
> Power & Cooling Supplies. They seem to be well filtered.
> http://www.pcpower.com/index.html
>
> By the way, something I did in my shack that significantly reduced
> noise pickup:
> - Any coax line that has to do with receiving I use 100% shielded RG6
> with a compression type F-connector. Where I didn't change to an F-
> female jack, I use an F-adapter to PL-259 or 1/4" phono.
> - Any coax line that has to do with transmitting I use 100% shielded
> Buryflex.
>
> It was amazing how much noise pickup dropped by getting rid of
> RG-213, RG-8X and RG-58 in the shack.
>
> N2TK, Tony
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Bill W5WVO
> Sent: Friday, January 11, 2008 11:58 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Computer Noise ruining 20 & 30m
>
> One thing to be aware of -- and I too have had quite a bit of
> undesired experience in this area -- hash from switching power
> supplies in computers is
> typically common mode noise, not differential noise. Consequently, a
> differential line filter often won't knock it down very much, if at
> all. What
> you need is ferrite toroids -- big ones -- around and through which
> you wind
>
> the power cord. In my case, the computer power supply is a 470W job
> in an ATX
> form factor, and because of the high power components, there wasn't
> any room
>
> in the PS case for filtering! So the RF noise from this PS was
> horrendous. It
> took TWO large ferrite donuts in series, with the ENTIRE power cord
> wound around them, to suppress the noise on 6M. I had bought a rather
> expensive differential noise filter for the line, and it did
> absolutely nothing. Brute-force common-mode filtering using ferrite
> toroids will usually cure the
> problem, but you may need a lot more saturability than you think.
>
> Bill W5WVO
>
>
> G4ILO wrote:
>> Alan D. Wilcox wrote:
>>>
>>> Hello,
>>> I gave away the feeble old PC I had by my radio equipment and
>>> replaced it with a newer one ...
>>>
>>> Now I have S9+ noise wiping out 20 and 30 meters.
>>>
>>> Using same keyboard, mouse, monitor; just the PC in a new case.
>>> Evidently it has a
>>> noisy switcher supply in it. Tried 110V in-line filter, also
>>> different 110V house circuit,
>>> but still have noise. Grounds don't help. Don't happen to have a box
>>> of toroids for chokes.
>>>
>> It's very likely to be the power supply, especially if it is a home
>> build or a local PC store build rather than a branded model. Most of
>> the PC cases and power supplies that home builders and small
>> assemblers use are made in China, and the manufacturers often leave
>> out all the components they can get away with, like anything to do
>> with interference suppression. I remember someone a few years ago
>> took apart a noisy power supply and could see all the holes in the PC
>> board where the suppression components should have been. It was quite
>> an eye opener.
>>
>> Replace it with a power supply from a decent manufacturer and all
>> should be OK.
>>
>> -----
>> Julian, G4ILO K2 s/n: 392  K3 s/n: ???
>> G4ILO's Shack: www.g4ilo.com
>> Zerobeat Ham Forums: www.zerobeat.net/smf
>
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