What are you using for test equipment? If I remember correctly W8JI has
stated that the MFJ 269B is innacurate on 160; check his web page just in
case.
If you have an accurate GDO available couple it to the antenna with a 1 turn
loop. Experiment with the number of radials but 2 should be sufficient for
the test.. The GDO will tell you where the antenna is actually resonant
without any reactance to confuse the issue. By knowing where it is resonant
then you know which direction to go with the matching network.
Im ordering parts for the K2PD VNA as Im tired of lugging a 50 # HP 8753B
and extention cord around. But a VNA is the best method to use.
Carl
KM1H
----- Original Message -----
From: "AB5MM" <ab5mm@9plus.net>
To: <towertalk@contesting.com>
Sent: Sunday, September 16, 2007 6:24 PM
Subject: [TowerTalk] 160m 1/4 wave vertical help needed
Fellow Top Banders,
I have a matching problem with a Rohn 25G, 160m ¼ wave vertical and am
hoping some of you can help me out.
<> The tower is 124'-9" in over all height. The tower bottom insulator
is located at 4'-3" above ground level thus making the vertical radiator
a total of 120'-6". All guy wires are insulated from tower as well as
being broken up throughout their length. <>
For now, the ground radial system is made of 22 each, 125' long, 14ga.
copper wire. I plan on installing another 14 radials next weekend.
Total number of radials will be 36 at 10 degree spacing. The soil here
in the Sabine River Valley bottomland has a "good rating" of 15mS/m. <>
My friend (K5ZO) and I have tried every thing we can think of to get
this antenna to resonate anywhere in the 1.8 to 2.0 MHz range. We've
tried both low pass and high pass "L" networks, a high pass "T" network,
low pass "Pi" network, and a parallel inductor with capacitor, in series
with the center conductor. <>
The best match we were able to achieve was with a 500pF cap in series
with center conductor. This gave us a 1.7/1 swr at 2.113 MHz. (R=64 &
X=31) All matching efforts have been made right at the tower feedpoint.
1. Is the tower too short?
2. Do we need to place a capacity hat at the top?
3. Would a short stinger out the top (for added height) help?
4. What about all the various matching schemes we've tried? Are we
missing something here?
<>Any input or suggestions would be greatly appreciated. Please feel
free to post to the group as I feel this information would be helpful to
others as well. <>
Thanks & 73, <>
Steve AB5MM
ab5mm@9plus.net
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