Tom
That's a lot of wire in the air...congratulations! Usually the more the better
but in this case it
sounds like too much. One approach would be to trim the horizontal top wire of
the L to get the +j18
close to 0. Then it would be a matter of matching the R to 50 ohms. You could
use a smaller version
of the tapped transformer shown near the bottom of this page:
http://www.w1vd.com/XNStxantenna.html
If a low SWR is important to you across the band you may want to shorten the
antenna beyond the j0
point and add a variable inductor in series with the vertical wire.
Jay W1VD / WD2XNS
----- Original Message -----
From: "Tom Boucher" <[email protected]>
To: <[email protected]>
Cc: "Finbar" <[email protected]>
Sent: Friday, August 03, 2007 5:30 AM
Subject: LF: Re: 500 / OLB test-sig...
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 -----
From: GW3UEP
To: [email protected]
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 -----
From: Gw3UEP
To: Tom Boucher
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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