[CQ-Contest] 160 NOISE

[Kenneth Earl Harker]

> My vertically polarized 160 antenna picks up 30-40 dB noise from some
> local buzz saw around here.
> That is what I weeded through last night.
> 
> I have seen several posted questions concerning some of the JPS and MFJ
> noise cancelling products out there from people with a similar problem.
> I have also seen promises to post real life experiences that potential
> users were going to pass on to the reflector after getting one of these
> devices. To date, I guess I have managed to miss these "results" postings.
> 
> Will somebody out there who has one of these things please tell me how
> well/poorly it works for you??
> Hearing nothing, I'll spend my money, but for which product?
> 
> 73,
> N5RP

     This isn't about 160 meter noise as such, but I can give you an example
of a noise situation where the JPS and MFJ noise cancelling units won't do much
good.  We've had a JPS unit up at N5XU before and generally found that it did 
not do much good.  Our problem is that being in the middle of an engineering
research campus in the urban center of a self-proclaimed "high-tech" town,
there are SO MANY noise sources that it would be worthless to even try to 
find the sources.  Unfortunately, this also means that a JPS or MFJ noise 
cancelling unit is worthless - even if we could knock out one signal, there
are still dozens of others out there.

     I've been playing around with the evaluation copy of FFT_DSP and made
some recordings and images last night after I failed to hear anyone on EME.  
Even I was surprised at what I saw it detect.  If you want to see what the 
bottom ten kHz of two meters looks like at N5XU (EM10dg), check out:

     (http://n5xu.ae.utexas.edu/vhf/vhfnoise.html)

     While these recordings are on two meters, which is one of the worst 
bands (432MHz is actually worse) we have similar noise on all the bands.
Fortunately, the HF bands are cleaner than VHF/UHF.

     My guess is that in any situation where you have only one noise source
that needs to be knocked out, it might be just as easy to go to the source.
And that if there's more than one source, the noise cancelling devices 
will have trouble being very effective.  

     From a contesting standpoint, you probably want to get rid of your 
noise source, anyway.  With the noise cancelling units, you need to retune 
them for each frequency, which would make scanning the bands a real pain
if the noise is bad.  

-- 
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Kenneth E. Harker      "Vox Clamantis in Deserto"      kharker at cs.utexas.edu
University of Texas at Austin                  Amateur Radio Callsign: KM5FA
Department of the Computer Sciences         President, UT Amateur Radio Club
Taylor Hall TAY 2.124               Maintainer of the Linux Laptop Home Page
Austin, TX 78712-1188 USA            http://www.cs.utexas.edu/users/kharker/
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