K5AF lives in San Antonio on a 75' x 100' corner lot. His general purpose
antenna is a tuned doublet that starts at the corner light post and goes
across his roof to a neighbor's tree in the opposite corner. His highest
tree is 40', all of them having been fresh-planted 5' saplings when he
moved in. Although he can easily tune the doublet in different
configurations to 160, his results on the doublet at 100 watts have been
considerably less than encouraging.
He has installed an FCP along the 75' back fence and has a mostly vertical
run up to 40 feet and then toward the front with a miscellaneous route to
get natural resonance with FCP+isolation transformer+wire. So basically he
is FCP and 40' vertical and rest low wire.
A couple nights ago, when the band was nicely open, 0430-0500Z he ran CQ's
and let RBN follow everything, doublet, then FCP/vert, then doublet.
Here's the results, best spot strength per RBN on antenna for the period.
W3LPL was the only one that was double faded on FCP. Doublet before and
doublet afterward were comparable. Paul is still working on the antenna to
reduce induction to stuff on his lot and is not done. At his power level,
on a "postage stamp" lot with minimal antenna possibilities, adding 7 dB is
huge.
K5AF RBN spots. San Antonio, TX
RBN Doublet FCP Vert Diff Loc
K3LR 16 dB 26 dB 10 PA
N0TA 19 dB 25 dB 6 CO
K8ND 17 dB 24 dB 7 OH
WZ7I 14 dB 23 dB 9 PA
KM3T 6 dB 21 dB 15 NH
WA7LNW 15 dB 21 dB 6 NV
NY3A 8 dB 17 dB 9 PA
NC7J 7 dB 12 dB 5 UT
N4ZR 5 dB 8 dB 3 WV
W3LPL 6 dB 6 dB 0 MD
AVERAGE DIFF: 7 dB
Unpaired readings:
WE4S 17 dB - - GA
KS4XQ 7 dB - - SC
W4AX - 26 dB - GA
W4KAZ did a more direct comparison. He took the antenna off a rig and just
let it sit in a corner of the shack, and noted the RX strength of 100 watts
on 20+ misc length on ground radials. Then he switched to the FCP, took up
all the radials and hit the key again. He had to reduce the power to 20
watts to get to the prior RX strength. Again 7 dB. This was verified
with RBN's vs local hams where prior diffs were known. In Keith's case,
the only available interpretation was that switching to the FCP and
isolation transformer removed 7 dB of induced ground loss, whatever the
method of induction, where ever it was.
Whether one wants to deal with an FCP or not, what should be more ominous
is that if you do not have a DENSE and UNIFORM radial field, you are most
likely dealing with quite more loss than you think. Models do NOT predict
this measured magnitude of change. They seem to severely underestimate
ground induction loss.
We will keep up the stories as they come in.
73, Guy
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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