[RFI] 160 meters RFI caused by low voltage bookcase lights

Don Kirk wd8dsb at gmail.com
Wed Oct 1 10:53:54 EDT 2014

Hi Paul,

My 4 turn shielded loop is very simple, and it's based on a design in the
July 1977 issue of QST by W1FB (the article was called Beat the noise with
a "scoop Loop".  My 4 turn shield loop is actually 14" in diameter (not
13").  I just created a simple website showing my shielded loop in detail
and the website URL is : http://sites.google.com/site/tunedloops/

I have numerous tuned loops and most of them are of the shielded variety
and I have one that is not shielded and it works fine too, but I really
prefer my 4 turn shielded loop due to its very low profile.  Very little is
required to construct the shielded loop (just coax, a piece of wire for the
pickup loop, a variable capacitor for tuning, and some electrical tape).  I
don't even care if it stays very round, etc.  Impedance matching
transformer helps, but when used with my W1FB preamp it really is not
needed, and when close to the source the impedance matching transformer
and/or preamp are not needed.  This system with my W1FB preamp can pretty
much hear anything my 68 foot base loaded TX vertical can hear on 160
meters.  More details on my website.


On Tue, Sep 30, 2014 at 12:53 PM, Paul Christensen <w9ac at arrl.net> wrote:

> "Portable direction finding equipment :
> DX440 receiver
> W1FB adjustable preamp
> Tuned 4 turn 13" diameter shielded loop (tuned to approximately 1.82 mhz)"
> Don,
> Great job finding the root cause.
> Perhaps you can tell us more about the shielded loop used to triangulate
> the source?  Any articles or construction notes?
> I have the National Vector Gun with the new 1.8 MHz loop together with an
> SDR-IQ receiver and notebook PC.  However, I'm finding that the preamp is
> adding more noise than signal.  The preamp peaks and tunes fine, but the
> noise floor covers up switching sources at the -110 dBm level.
> I'm looking for a more efficient antenna for this purpose and may try a
> Pixel Loop for locating low-level switch-mode sources, then move to the Gun
> when getting close.  Your noise source was severe enough (S9+) that you
> overcame this issue with the small diameter loop.
> I once owned a Palomar LA-1 loop system and that allowed me to locate many
> low level noise sources.  I sold it, thinking the Vector Gun would do a
> better job.  Hindsight is 20/20 and I should have kept the LA-1 before
> trying the Vector Gun.
> Paul, W9AC
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