This thread is very interesting to me since I have a tower and hope one
day to be able to use it for LF transmitting. The antenna that I used
last year for the first TA receptions was my 160 meter dipole which is
suspended from the tower at about 30 meters above ground. The top of
the tower is a few meters above this point and there is a mast with H
frame supporting VHF/UHF and microwave antennas. The feed point of the
dipole is offset from the tower approximately 0.75 meter. The feed line
is homebrew ladder line which maintains the 0.75 meter spacing from the
tower down to near ground level. The ladder line is pulled tight so
that few spacers and no additional standoff supports are required. The
antenna works great for all HF bands when fed with a 4:1 air balun and a
4 meter section of 7/8" Heliax connecting the balun to a tuner in the
shack.
A few months ago I connected the tracking generator output of the HP SLM
that I use for LF receiving to the 160 meter antenna. I removed the
balun and tied the balanced line wire together then inserted a small pot
core coil in series with the antenna. With another antenna connected to
the SLM input I adjusted the tunable coil to resonant the antenna. The
SLM was tuned to 135.922 KHz TA window from the previous evening
receiving session.
Not long after performing this adjustment I received an email with
screen capture asking me if I knew what that signal was in the TA
window. The time and frequency confirmed it was my signal. This
reception report came from a station 543 KM away at mid day with the
generator power of 0 dbm! I knew this arrangement worked fairly well
for receive but to find it would radiate so well was a surprise. I
thought most of the signal would be shunted to ground since the
radiating wire was so close to the tower.
Now my question to the few who have read this far. Can I expect this to
be a good high power transmitting LF antenna with the addition of a good
coil? All cables from the tower route down to about half a meter above
ground where they run horizontal under the shack floor. I suspect these
cables would be hot with RF unless they are choked off by some method.
The tower has insulated guy wires but the base is well grounded. The
top of the 160 meter antenna can been seen on my VHF or Microwave page
at: http://www.gostanly.com/w4dex/ The top support is on the left
side of tower just above the top guy wires.
Dexter, W4DEX
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