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Rog (and others) - thank you for this. You may, or
may not, be interested in the matching arrangement for my antenna.
The antenna is an extension of my 160 metre
inverted 'L' which has an 80' vertical section to a tree on a 20' bank - the
effective height may therefore not be as much as 80'. This antenna sits on 19
radials which are 60 - 100' long and are either buried or lying on the ground,
in order to act as trip wires for my XYL when she trespasses on my antenna
area.
An additional 358' has been added to this antenna
to make the total quarter wave length of 492'. This added wire zig-zags for 50'
or so then is largely in a straight line held up by 3 further tree halyards and
ends up about 30' above ground.
This antenna with no matching showed a minimum VSWR
at 506KHz of 2.5:1 and impedance of 22 + j18. By empirical means (!) I
established that a parallel capacitance of some 6000 pF brought the SWR to a low
figure but, not unexpectedly, took the resonant frequency up to 521KHz; an
L-section using part of the antenna's self-inductance. To bring the antenna back
down to 502KHz, I added a small inductance between capacitor/coax and the base
of the antenna.
The final values were 9 micro-Henrys (22 turns on
1'' dia) and 6,600pF (3 x 2,200 pf 1000v polypropylene) giving 1.1:1 @ 503 KHz,
50 + j10.
I was surprised at the high value of capacitance
needed to resonate this antenna and am not sure how you go about calculating the
necessary values as these were established by trial and error. Perhaps there is
an academic out there who can tell me!
73, Tom
G3OLB
----- Original Message -----
Sent: Friday, August 03, 2007 8:55
AM
Subject: LF: 500 / OLB test-sig...
Tom,
Hrd your test-loop ydy - steady S7 on meter - ur
tidying up has wrkd!
Ur closing the gap on Mike [S9/40mls via
Preseli mountain] over the ~90mls part sea-path bn us.
Hope to improve ant nxt wk, jobs
permitting.
Rog.
----- Original Message -----
Sent: Monday, July 30, 2007 2:18 PM
Subject: Re:
Tom - what hve u done? Fantastic sig nw -
on meter S5/6...
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