[Lowfer] MP on 137 kHz

[Lyle Koehler]

I have posted another capture of Mitch's signal at
http://www.qsl.net/k0lr/MP137-0211.jpg

This capture was taken a little before sunrise, when there was skywave
propagation to much of the US from my location. I believe I have correctly
identified the Loran signals, although it is hard to explain the apparent
"selective fading" on lines from the same chain.

As Mitch says, thanks to the efforts of John Andrews and John Davis, we can
now identify the Loran clutter on the screen, and find clear areas in which
to operate. Last night I copied the frequencies from the list in the
immediate vicinity of 137.780 kHz, pasted them into Excel, and created a
chart showing their relative positions. Then I opened the chart in
CorelDraw, stretched it so that it exactly matched the scale of the Argo
screen, and printed out a template that can be held up to the screen to
identify the Loran signals. This proved to be more convenient than reading
the frequencies from the text version of the list, since there are about 25
possible Loran lines on the 1024 X 768 version of the Argo screen in
30-second dot mode. It was immediately apparent that something was wrong,
because after sunset my screen showed many lines that just didn't fit. I
suspected that my "universal" preamp (used in combination with a 10-foot
single-turn loop) was being overloaded and was producing intermodulation
products. Switching to the "mobile" version (J310 FET and 12-volt supply) of
the AMRAD active whip, most of the crud disappeared. Without the help of
John's list, I would have blamed all of those lines on Loran! Now I need to
make the universal preamp more "bulletproof" -- it works much better than
the active whip in the 160 to 190 kHz range, but obviously has problems when
it gets down into 137 kHz territory.

Lyle, K0LR