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Re: [RFI] Poor man's portable spectrum analyzer

To: "David Eckhardt" <davearea51a@gmail.com>
Subject: Re: [RFI] Poor man's portable spectrum analyzer
From: "Charles Gallo" <charlie@thegallos.com>
Reply-to: charlie@thegallos.com
Date: Fri, 13 Jul 2018 13:22:11 -0400
List-post: <mailto:rfi@contesting.com>
On Fri, July 13, 2018 1:06 pm, David Eckhardt wrote:
> I have never been able to display more than 8 MHz with the SDRPlays.
> However, with the AirSpy using the SpectrumSpy application which comes
> with a download of SDR#, I am able to display on one screen from roughly
> 25 MHz
> through 2 GHz.  Of course, you can display less if desired and zero in on
> specific 'signals' when desired.  I have no connection with AirSpy other
> than owning 3 of them.
>
> Dave - WØLEV

My question is not the SDR (I have one running), or even "How the heck did
you get it running on an rPi (software etc) but...

I always see references to loop antennas, and have even seen a few links
to plans.  They all use a variable cap to tune the resonance, but they all
seem to use different values etc.
Assume I'm going to a hamfest this weekend, and I'm walking around and the
usual vendors have bins of variable caps, everything from small little
things, to huge ones with 20-30 plates that look more like what you see in
an amp or an antenna tuner.  They don't seem to have markings similar to
what a fixed cap has (either XXXmfd/pdf or 103/104 - which I understand). 
How do I pick a cap, and if necessary, tweak the design of the antenna

Right now, I'm not very radio-active (need to get my replacement rotor
installed, but I can get on 17m and 80m without that), but I like to help
my friends with RFI.  I DO have various receivers, and even have an Arrow
2m beam and attenuator, but something for HF/MF isn't in my kit


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