First thing is to get rid of that 75' of cable. Measure it right at the
base, otherwise you have to transform all the impedances back through that
cable to know what you really have. And since the mjf meters are useless I
assume you are using only an swr bridge, that can't show you the actual
resonance especially after going through a cable.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of AB5MM
> Sent: Friday, September 28, 2007 00:52
> To: towertalk@contesting.com
> Subject: [TowerTalk] 160m 1/4 Wave Vertical Results Thus Far...
>
> Gentlemen,
>
> I would like to extend a hardy "Thanks" to each of you that responded to
> my plea for help with matching the 120'-6" 160m Rohn 25 Vertical. It's
> still not working like I think it should, so let me tell you what we've
> managed to accomplish to date.
>
> 1. We now have 40ea. 125' long ground radials installed. Another 20 will
> be added this weekend for a total of 60. I think I'm going to say that's
> enough for now. NOTE: Going from 22 to 40 ground radials made little
> difference!
>
> 2. Both the MFJ-249 and MFJ-259B are virtually useless at these
> frequencies. Too much rf from the BC band. This alone would have saved
> us hours in trying various matching networks, not to mention the number
> of "Pepcid Complete" ingested.
>
> 3. In sweeping the tower from 1.600 MHz to 2.500 MHz, we found it's
> natural (no matching other than the 75' of LDF4-50A) resonance at 1.788
> MHz. The lowest swr observed at this frequency was 2.6/1. At 1.800 it is
> 3.0/1 and slowly rising to 4.0/1 at 2.000 Mhz. Conventional wisdom tells
> us that the thing is too long (tall). This still brings up the
> question, "How can this be the case when the vertical is only 120 ft.-6
> in. tall to begin with?" What are we missing here guys? The center of
> the band (1.900 mhz) is what we've been shooting for all along.
>
> 4. A high pass "T" network brings the match down flat, but it's Q is
> high enough to only realize a practical band width of ~33kc.
>
> 5. A low pass "L" network works as well and exhibits a little larger
> band width of ~60 kc. Our goal is ~100 kc wide... is this reasonable?
>
> We really don't know what to do or try next, if anything. Should we be
> satisfied with what we have?
>
> Press on, nothing is as persistent as persistence itself.
>
> Tnx & 73,
> Steve AB5MM
> Lloyd K5ZO
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