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Re: [RFI] Noise...

To: Jim Brown <jim@audiosystemsgroup.com>
Subject: Re: [RFI] Noise...
From: "Kenneth G. Gordon" <kgordon2006@frontier.com>
Reply-to: kgordon2006@frontier.com
Date: Thu, 13 Mar 2014 12:10:26 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 13 Mar 2014 at 10:47, Jim Brown 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.

It certainly is both of those: however, I already own it. 

I don't have the other stuff, and really shouldn't spend the money on it 
although, believe me, I wish I could..

. 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.

That is certainly all very good advice and that is good information. However, 
at this point, I FIRST have to determine where the crap is coming from. At 
this point, I have no clue.

> 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 --

Exactly. At this point, I am hearing it best in the 80 meter band. Therefore...

> 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.

Yes. Understood.
> 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.

Again, yes. I have understood that.

> 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).

In fact, even using a BFO makes the noise much less "clear". AM seems to 
provide the best way to recognize it.

At this point, I do not (yet) have a VHF receiver (except one of the 
Stoddart's) which has an AM detector.

The NM-30 covers from 20 MHz through 400 Mhz, but it ain't small, and it 
sure as heck aint very portable either.

The NM-20 is at least "reasonable" in size, requires low power (25 watts or 
less), can be battery powered (although I would have to "make" the 
batteries), and was designed to be at least semi-portable. After all, it has a 
handle on top. ;-)

One of the best things you can say about it is that it is EMP proof.

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