Jeff,
You need to obtain a digitally tuned shortwave radio that you can tune
down to the frequency range you are concerned with, and preferably one
that you can tune down to around 9-10 kHz.
You can also use a spectrum analyzer such as the older Tektronix 7L5, or
somethng more modern such as the ESA, PSA, XSA, RTSA, or SDR (fairly
expensive). If you are just getting started in TSCM the Tek 7603
mainframe with a 7L5, 7L12 or 7L13 and a 7L18 set of plug in will give
you an inexpensive measurement solution.
Either way you want to start by measuring the signal that is half the
frequency you are interested in (in this case 18.5 kHz), and then measure
3x and 4x this frequency (in this case 55.5 kHz and 74 kHz). What you are
trying to do is see if the 37 kHz is a harmonic of a lower frequency
signal, or is it the fundamental or originating). Once you determine what
the original signal is you will want to measure each of ten or more
harmonics up the spectrum from the fundamental (up to at least 370 kHz in
this case).
At the frequencies you mention I would suspect that the signal is
originating from a florescent lighting fixture or bulb, but it could also
be part of the meter-reading system for his water or electric
meters.
If is also possible that the frequency meter is malfunctioning, and also
possible that what you are picking up is the sub-carrier signal of a
local FM radio station (at 38 kHz) that is being pickup and rectified on
the building wiring, or that you are very close to a military base and
are picking up of VLF/ELF transmissions.
In any event your going to have to determine exactly what the frequency
is of the originating signal, the harmonics involved, and the exact
voltage levels involved, and what kind of modulation (if any) is
present.
To provide an optimal pickup of the signal you will need to use a
shielded magnetic lop antenna, tunable bandpass filter, and a
pre-amplifier.
-jma
At 03:57 PM 1/30/2008, Fax..._at_aol.com wrote:
Folks, I need some
advise from the more experienced in the group. I am new to TSCM.
A client has an RF field throughout his house. The RF field
radiates/reflects from every metal object in the house. The house wiring
radiates through the electrical outlets, light switches, etc. Even towel
racks, and door knobs are radiating the field to some degree.
I have been able to determine that there are more then one frequency
involved. I get a 37khz measurement, and higher.
He is concerned about a bug, and the health aspects of a RF field in the
house.
Il have to re-check after I get some advise as to what to be looking
for.
The electricity went out in the house and the general neighborhood.
Measurers indicated that the RF field was still present. It is always
strong enough to cause the RF receiver to show a field. Its only a matter
of intensity.
I have thought I located the transmitter, only to find I found a pipe
running up through the hosue up to the attic and venting out the roof. It
was just radiating the RF.
What must I look for, what can this be. There is more then one frequency
at work hear. I need advise as to how to proceed on a major
budget.
Ideas?
Thanks-
Jeff Warshal
FaxTrac Information Services
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Phone: (978) 546-3803
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Fax: (978) 546-9467
127 Eastern Avenue
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Web:
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Gloucester, MA
01931-8008
E-mail:
mailto:jm..._at_tscm.com
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Received on Sat Mar 02 2024 - 00:57:23 CST