Hello Folks,
Here in the New England area of the USA there have been a number of
experimenters trying loops in the LF band.
I have been experimenting with a 200' length(50 feet on a side ) of
#24wire 100 pair of telephone cable. A total of 200 wires woven
specifically to be minimize crosstalk between pairs and common mode
interference.
I thought that this may approximate a "Poor Mans Litz Wire". After
carefully stripping and solders all the wires, and terminating them into a
1" copper braid, I installed the 60 plus pounds of wire into a diamond
shape on my tower.
After resonating the loop using silver mica's and measuring the -3db point
with a selective voltmeter the antenna had a dismal "Q" of 61 !! Others
using similar setups but different conductors have measured "Q" of 180 and
above. Also the slope either side of resonance was not smooth at all, there
seemed to be peaks among the slope. When looking at the current and voltage
waveforms at the feed of the antenna, using the test tool described in the
LF handbook, it could be seen that a the current was a perfect sinewave but
the voltage waveform always had a flat top or a double peak. Changing
resonance or turns on the matching transformer would only changeflat spot
slightly. Loop Rac measures 1 Ohm based on matching transformer ratio.
Now the loop is on a tower that is 130 feet tall. The guy wires are not
broken up with insulators. So is it possible that there is a resonance in
the guy wires causing the double peak?
/If so why only on the voltage wave forms? This test unit built by W1VD has
been used to adjust his antenna and this does not seem to be a problem with
his antenna.
That was some background, here are my main questions.
A) When visualizing the losses from the earth in a vertical antenna system,
they would appear to be in series with the Radiation Resistance, thereby
limiting the current that thae antenna can draw. Is this statement true?
Current flows from the radiator and returns through the earth(limiting the
current) which is lossy and thus making a poor radiator.
B) How does the earth effect the a loop? Does it look like a lossy
secondary of a transformer? Since the loop is "closed" is cannot be truly
in series with the antenna.
Perhaps the affect is a reflected impedance from the ground causing current
to flow in the antenna. In a loop the Rac is determined by the radiation
resistance, in series with the loss of the capacitor, in series with the
loss in the inductor and an unknown series loss for the earth. Is this
true?
The antenna I have radiates but not well. Will be experimenting with other
conductors and also locating the antenna away from the tower.
Please comments
Thank you
PaulC
W1VLF
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