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

To: rfi@contesting.com
Subject: Re: [RFI] Poor man's portable spectrum analyzer
From: "Dave Cole (NK7Z)" <dave@nk7z.net>
Date: Fri, 13 Jul 2018 10:48:01 -0700
List-post: <mailto:rfi@contesting.com>
Getting slightly off topic, this might help:

http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx

73s and thanks,
Dave
NK7Z
https://www.nk7z.net

On 07/13/2018 10:22 AM, Charles Gallo wrote:
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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