[TowerTalk] 160m 1/4 wave vertical help needed

[donovanf at starpower.net]

Steve,

Your symptoms make me suspicious that your antenna may be fine and your
impedance measurements may be bad.  What instrument are you using to
make your measurements?  MFJ analyzers and many laboratory instruments
are easily overloaded by strong signals that may be present on your
antenna.

Suggest you try an instrument that operates at transmitter power levels,
such an a VSWR meter or an LP-100 Digital Wattmeter (my favorite),
before you pull any more hair out.

73!
Frank
W3LPL


---- Original message ----
>Date: Sun, 16 Sep 2007 17:24:05 -0500
>From: AB5MM <ab5mm at 9plus.net>  
>Subject: [TowerTalk] 160m 1/4 wave vertical help needed  
>To: towertalk at contesting.com
>
>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 at 9plus.net
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