[RFI] New RFI source for me...

Frank N. Haas KB4T utility.rfi.pro at gmail.com
Sun Jul 24 13:27:38 EDT 2016

I'm not familiar with the Alex loop so I can't comment on how it compares
to the National RF loop system.

I like the National RF system because I can walk with a receiver in one
hand and the vector gun with loop in the other. The vector gun is easy to
carry and small enough to be easy and convenient to use.

The National RF system includes a tunable amplifier that both increases
gain to hear weaker sources or attenuate stronger signals. Thus I rarely
need to carry a separate attenuator.

The kit includes multiple antenna loops. This provides improved sensitivity
at any particular frequency.

If the Alex loop offers these advantages and costs less than $300 to build
or buy then it may be a good choice.


Frank N. Haas KB4T
Utility RFI Investigator

On Jul 24, 2016 12:18 PM, "Dave Cole" <dave at nk7z.net> wrote:

> On Sun, 2016-07-24 at 11:36 -0400, Frank N. Haas KB4T wrote:
> > I will not speculate as to what the source might be. As I have said in
> > this
> > forum many times, I consider such attempts to be a complete waste of
> > time.
> >
> > However, I will say that the periodic character of the source should
> > make
> > it easier to find. If the highest frequency at which this source can
> > be
> > detected at your location is 4.0 MHz, options are limited. The first
> > tool I
> > would use is a battery operated receiver and the National RF HFDF
> > Vector
> > Gun active loop antenna kit.
> >
> > You don't describe the antenna or radio equipment being used to hear
> > the
> > source. You also don't describe the  relative signal strength though
> > from
> > the audio recording it would seem that the source is fairly strong. It
> > may
> > be difficult to hear the source on any portable receiving system. If
> > so,
> > you may have to perform an expanding circle or square search to find a
> > location where you can hear the source well enough to begin
> > pinpointing it.
> >
> > I have been faced with this kind of source many times over my RFI
> > investigation career. Patience, good record keeping, more patience and
> > an
> > open mind are essential.
> >
> > Don't waste time trying to guess what this source might be. Find it.
> > Then
> > report your findings.
> >
> > Each time one is involved in a search of this sort, the experience is
> > valuable, educational and, when successful, very satisfying.
> >
> > Good luck and good hunting.
> >
> > Frank N. Haas KB4T
> > Utility RFI Investigator
> > Florida
> >
> Hi Frank,
> I will be doing exactly as you described as soon as my part arrives from
> Tarheel, the low band antenna for the truck is dead at the moment...I am
> just trying to get a feel for it is all and hoping someone had heard
> this sort of signal at some point.
> To your point about equipment-- K3, and a Gap Vertical.  I already tried
> with a portable SW reciever, and you are correct, not strong enough.
> The signal is about S7, or -90db at the antenna here.
> You mentioned the National RF HFDF Vector Gun active loop antenna kit,
> is it much better or worse than an Alex loop?  I have been looking at
> that for a while now, and considering building one, but with summer
> coming to an end soon here, I might get it if it really works.  Could
> you comment on it please?
> --
> 73's, and thanks,
> Dave (NK7Z)
> For software/hardware reviews see:
> http://www.nk7z.net
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