For those that don't want or can't build a suitable loop antenna
system to track HF RFI sources, I remind the group of the National RF
model HFDF Vector Gun active loop antenna system that has served me
very well in my professional RFI location efforts. $240 plus shipping.
I've written here about this tool. Do a search and you can read my comments.
73,
Frank N. Haas KB4T
Utility RFI Investigator
Florida
On 3/13/14, Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 3/13/2014 10:05 AM, Kenneth G. Gordon wrote:
>> The NM-20B, which is a high-quality, 7 band, receiver, with switchable
>> BFO,
>> tunes from 150 Khz through 25 MHz, and includes various "input devices"
>> including a shielded tuned loop, and a device to allow the input to be
>> connected directly to the AC line.
>
> That's a lot of effort to resurrect a box that is probably obsolete and
> may not be very portable. K1TTT's advice to use a RX with a ferrite bar
> or shielded loop antenna is a good one. Likewise his advice on using a
> shorter antenna, or no antenna at all as the noise gets stronger. The
> Kenwood TH-F6A DOES have in internal ferrite loop antenna, and it is the
> default antenna below 10 MHz. If I didn't have one of these talkies, I
> would use a portable consumer radio that has AM RX capability at VHF.
> The Tecsun PL660 tunes the AM Aircraft band around 120-130 MHz. It's a
> VERY nice consumer radio, and costs about $130.
>
> Remember this fundamental fact -- if the noise source is ELECTRONIC
> (computer, switching power supply, battery charger, plasma TV, etc.) we
> MUST chase the noise on the frequencies where we are hearing it -- that
> is, the ham bands; but if the noise source is impulse noise generated
> by arcing, mostly in the power system, we can chase it most effectively
> by listening at the highest frequency where we can hear it. THAT'S why
> we listen with an AM detector, why we start listening at VHF, and why we
> try to listen at UHF when we get close to the noisy pole.
>
> Why is UHF important (and useful)? Because arcing produces noise that
> extends well into the UHF range. Lower frequency components are carried
> along power lines, a very long line can be the radiator, and we even
> hear standing waves along the line. But the highest frequency components
> don't travel well along a line, so the wiring very close to the source
> becomes the most effective antenna. Thus, when you hear impulse noise
> will at UHF, you're very close to the source.
>
> Why is AM detection important? Because the noise is AM, and FM
> detectors inherently reject AM (although they do detect AM a bit by
> slope detection -- the variation in signal strength with frequency).
>
> 73, Jim K9YC
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>
--
Frank N. Haas KB4T
Utility Interference Investigator
Florida
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