Hi all ...
I took some readings using 3 different antennas and there's the
results:
# Antenna 1 - 1 turn copper loop, 12mm rod, octagon, 4.8m perimeter
(1.2m
"diameter")
# Antenna 2 - 80 m inverted vee, apex at 30m high
# Antenna 3 - ferrite loop, 10mm dia, 7.5 inch long, all extension
covered
by 26# magnetic wire, varactor tuned and MPF102 push-pull preamp.
I'm trying to verify if I can use a single turn tuned copper loop
instead
the "n" turns thinner wire ones.
Rejloop1, Rejloop3 and Antenna Optimizer gave more or less the same
efficiency X tuning C X impedance for all loops.
The 1 turn unit have a broadband step-up ferrite transformer (25 X
1/2 turn
ratio) using some 1800 ui core, those box shaped built to remove EMI
from a
25 way computer flat cable (1.5 inch long X 1.5 inch wide X 1/2 inch
high).
So this xformer is able to handle 0,0XX ohm on its primary (a 1 inch
wide
copper stripe). I need to make some measurements on it to be shure
about
this.
A local NDB was used as signal source, on 260Khz. The "dBmV" reading
is
relative audio out from my receiver (a ITT Mackay Marine 3026). The
dBu
readings came from the S Meter. For audio readings, AGC = off.
So:
# Loop + xformer, tuned (like the isoloop) = 0dBmV (18dBu)
# Loop + xformer, un-tuned, capacitor shorted = -7dBmV (12dBu)
# Loop w/o xformer, feedpoint un-tuned straight to 50 ohm feeder = -
22dBmV
(5dBu)
# Loop w/o xformer, feedpoint tuned straight to 50 ohm feeder = -8dBmV
(14dBu)
# 80m dipole = +2dBmV (20dBu)
# Ferrite rod = (+15dBu)
I'll repeat those readings on a 4m diameter aluminum loop, 17mm tube,
as
soon as I finish my remotely controlled capacitor decade circuit (1nf
steps
from 0 to 350nf). Seems that the 1 turn solution will perform well -
and the
best part - no pre-amp, but the decade C :o(
73
Marcus, PY2PLL(Base) / PY3CRX (Mobile)
GG66rf - S. B. do Campo - SP
hampage => http://py.qsl.br
e-mail => [email protected]
Active from DC to
24GHz
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