[RFI] Noise...

[Edward Sawyer]

I have very successfully used a 6 el 432/4 el 144 duo band yagi - hand held
with a Yaesu VX1R in AM receive mode and headphones.  My experience has been
to see if you are beaming power lines or a point source.  If it is suspected
to be a point source, then follow your station directional antennas but if
its actually pointing to power lines, then suspect the power line is the
radiator and not the source....but the source is on the line some where and
walk the line sniffing at these much higher frequencies.  They are almost
always less than 1 mile from your station from my experience.

73

Ed  N1UR

-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Kenneth G. Gordon
Sent: Thursday, March 13, 2014 3:10 PM
To: Jim Brown
Cc: rfi at contesting.com
Subject: Re: [RFI] Noise...

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
either, 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.

Ken W7EKB
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