[Lowfer] Successful Antennas 137 Khz With Near-Field Issues

[Laurence KL7 L]

HI David - Like the other responses I ran/run an "Ashlock loop" -  Bill and others were very supportive and I had to get used to a different type of RF engineering with high Currents involved -


As per others resonating was with a bank of current Sharing Sangamo G2/G3s (or Aerovox etc) and a Russian 20-1000pf Vacuum variable motor driven from shack. 3 X 290-77 ferrite cores (bytesmark) , individually insulated then stacked and a 2:13T transformer (switched secondary's from 2-16T) and the ubiquitous  - W1TAG current monitor, Tuning was pretty stable


 First implementation for 137kHz was in a small postage sized garden in a rental in Oklahoma in 2004 -  favorably it had two trees spaced over 100ft apart - slung 3 or 4 parallel thick 8/6 TTFN over nice slidy branches of  the Cottonwoods and paralleled  them - with 3W ERP this loop made it to XES for a WOLF qso and pretty much covered the US and over the borders. Also across to Eu and visually down to ZL over many months of the year - so it "worked" pretty well. The ground and open aspect helped here I think (akin to K5DNL qth)


I have a bigger loop here (there) in Alaska around 600ft with 65ft verticals and lower return at 9ft, and 1W EIRP capable it appears to struggle to be heard but this is down to remoteness ie geography, iono ( a lot), ground conditions etc. Even so its made it to JA this year on WSPR and visually to ZL, and pretty much every night down to the PNW at plus 2000Kms, but as 475 rarely breaks out Eastwards.  Most of  this "this antenna doesn't appear to work up here"  is propagation at this/that latitude but close in mountains limits low angle stuff, if there is much with the loop (!) - same for 475kHz.


Loop conductor in Alaska is a single run of either 4 or 6TFFN - electrically this isn't the most efficient use of copper but strength wise keeps the trees in order.  The broadside  null is pretty sharp and Ive yet to decode KL7L here on Hawaii; Tuning is very stable and I can safely run remote ops without too much fear of fire...tempting fate there....


Aloha Laurence KL7L/KH6

ps XXP was a good signal on 137 from here on a noisy night - but no Cigar for KL7L


________________________________
From: lowfer-bounces at mailman.qth.net <lowfer-bounces at mailman.qth.net> on behalf of David Stinson <arc5 at ix.netcom.com>
Sent: Sunday, February 25, 2018 6:59 AM
To: 'Discussion of the Lowfer (US, European, & UK) and MedFer bands'
Subject: [Lowfer] Successful Antennas 137 Khz With Near-Field Issues

Is there a list somewhere of the antennas used by
those successful in QSOs on 137 KC, and how they
have dealt with near-field problems like
tree-covered lots?  I've heard people say a
transmitting loop worked well and others say it
was useless.  Is there a consensus on antennas
with near-field obstructions?

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