On 22 Mar 2014 at 14:19, Tom Thompson wrote:
>
> Hi Ken,
>
> Looks like you are making progress. If your loop is not sensitive enough, you
> might try building one of mine. The big loop is sensitive enough when tuned to
> give a good signal when the noise is about S-7 on my dipole.
>
> Good luck,
>
> Tom W0IVJ
OK. I'll take a look at it asap.
Our oldest son, Brendan (KB7QEU) who is a good statistician, and I took the
NM-20B and went hunting. We found two different types of noise and two
different directions to the sources.
Since I was not able to really DF the noise at the 80 meter frequency where it
is most noticeable (about 3570 KHz) on the FT-890 and my transmitting
antenna, I kept tuning the NM-20B lower and lower until I found a maximum
at two frequencies about 20 Khz apart: 300 and 320 kHz, with that at 320
KHz being about 3 X stronger in signal strength than the one at 300 KHz. We
called them Noise #1 and Noise #2. Unfortunately, since they sound nearly
identical, I am not sure they really aren't the same source.
Practically every where we set up, there was at least one pole-pig within 1/2
block, and we did not find even ONE of those which didn't hit 50db on the
rod antenna, which pretty much made that useless.
The loop was a different story, however.
We got some very clear directions on Noise #1, which seemed to center it
very near or in a new laboratory building built within the past 6 months and
only two blocks from us.
Noise #2 seems to be centered around a very large, three-transformer,
mini-substation which is installed just to the rear of the Rosauer's
supermarket about 3 blocks away.
My best inclination is to want to DF the noise at the frequency that is
bothering me the worst, which would be about 3570 or so.
Therefore, it seems clear that I am going to have to build a loop dedicated to
this frequency-range and a preamp to go with it.
Surprisingly, the NM-20B is working very well, its loop works extremely well,
and I am pleased with its performance, although it is more than a little
"clumsy" to set up and use. It also needs a good alignment, which I will do as
soon as I can.
To power it, I am using a 75 watt 12 VDC to 110 VAC inverter which is
specified as being fully in complicance with FCC Part 15B rules for noise,
and so far, it appears to be very quiet.
The NM-20B when running on AC draws less than 25 watts.
I am about to enlist the aid of another ham here, a younger man who works
for the best company (in electronics) in the area, and who volunteered to
help.
More later.
Ken W7EKB
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