Hello Mike,
For over a year, I had a problem with 'noise hills' mostly on 40m. The
peaks were spread approx 60 KHz apart and their amplitude was about 10
to 15 dB above the normal noise floor. They would go away completely
every few days for a couple of hours, but they always came back again.
I had determined that the source was outside my house, so what I really
needed was a directional antenna for 40m. I built a simple 2' diameter
magnetic loop which has extremely sharp nulls perpendicular to the plane
of the loop, and tuned it to 40m. Took my FLEX-3000 (attached to a
gel-cell) and laptop outside on the front lawn, and rotated the loop and
could definitely produce a null to the point where the noise
disappeared. Moved the entire setup about 100' away and did it again.
Triangulating, it pointed to a side-wall on a neighbors house across the
street. I moved the setup over to within about 15' of the house, and the
noise increased dramatically.
I spoke w/ the neighbor who was extremely cooperative, and learned that
he had three computers along that wall of his house. He was gracious
enough to allow me to investigate, so I brought my Kenwood TH-F6 HT
(tuned to 40m) into his house and we found the offending computer in
short order. I pulled a known high quality (and expensive) power supply
from one of my computers and we swapped out his power supply with it,
and the noise completely disappeared! I asked him to *please* keep the
power supply, and let me have the old one. He agreed, laughed, and asked
what I was going to do with the old one, and I told him I was going
disable it so that it would never find its way into another computer
again. It is now a small fraction of it's original height.
So ... I'd strongly suggest that you do a little noise hunting with your
FLEX-1500 attached to a magnetic loop antenna. These FLEX radio's also
make wonderful lab instruments.
73, Dale
WA8SRA
Mike WA8BXN wrote:
I have noticed at times (particularly during fox hunts) what I can best
describe as a noise hill that usually drifts around in frequency. For a
width of several KHzon the panadapter I see what is shaped like a "normal
curve" that trails off for many more KHz. In panfall mode I can see a
brightening where the curve in the panadapter display.
Sometimes, when the peak of the curve is in the passband of the receiver I
can hear a shift in the noise frequency at around a second or two intervals
as the peak drifts around.
I have observed this with both a 1000 and 1500 flex radios. Disconnecting
the antenna gives a flat display. Connecting a wire to the antenna several
feet long just in the shack does not show the noise hill, so it doesn't look
like its something in the shack.
The effect happens with a number of antennas and is not consistent at all. I
live in a rural area with other houses hundreds of yards away.
Has anyone else observed this sort of thing or have any idea what it might
be?
Thanks in advance!
73 - Mike WA8BXN
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