"The Supervisor of Power Distribution in Idaho Falls (nearest town to
my
Idaho QTH) called to ask if I thought they should buy a Radar
Engineers
Model 240 RFI/TVI location system. (Shown at www.radarengineers.com )"
"Tod, K?TO"
Tod,
It sounds like a very handy gadget, but a couple of caveats are in
order. My company owns a portable EMI receiver made by Rhode &
Schwartz. It covers the 25-1000 MHz part of the spectrum and is a
decent broadband receiver. It's calibrated in dB?V and has AM and FM
detectors and an accurate attenuator. Our bench tests showed the
sensitivity to be quite good.
When used with the antennas that are sold with it, the receiver is
almost useless. The hand-held antenna mount has a built-in preamp and
signal level meter (also calibrated in dB?V). Although the antennas
seem to be directional, they are extremely inefficient--so much so
that I have had trouble finding fairly strong electrical noises I knew
were present. Substituting a 439 MHz Cushcraft 11-element yagi makes
the receiver useful.
The moral of the story: Even if the receiver specs are good, the
system might be useless if the compact antennas don't work well. They
should get a demonstration before spending their money.
One additional thought: This outfit will be good for locating sources
on relatively low-voltage power lines, for example the 14.4 kV lines
that distribute power in residential neighborhoods. However, in
locating problems for one of our local power producers, we have found
that "high tension" lines--the ones that operate a 100 kV and
up--produce emissions at much lower frequencies. I have found peaks
at 330 kHz, 470 kHz, and on up through 1800 kHz, when no emissions
were detectable in the HF, VHF, & UHF ranges. There are harmonics of
course, but the fundamental emissions seems to be related to the
voltage on the line and the size of the insulators.
BTW, my company has bought an FT817. It's as useful as the $20k R&S
receiver, and with a loopstick preamp/antenna we've built, it's sensit
ive down to 100 kHz. Heck of a deal.
73,
Brad, KV5V
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