Carsten,
I just received a new set of 40M phasing lines from Comtek to
replace the 10yr old lines that were showing a lot of age. Jim
Miller builds these lines using a network analyzer to get the
lengths exact for 7025kHz. I connected each line to the MFJ-259B
(without a tee or resistor) and they all showed zero-ohms right at
7.025mHz +/- 10kHz. The lines were all within 1" of each other.
The older lines (approximately the same lengths) had been buried
between the control box and each radiator. Fresh out of the ground,
they measured somewhere around 6.5mHz (prompting me to replace
them). After a week on the concrete patio in the hot KY sun, I
remeasured them, and they were very close to the new cables.
Lessons learned: 1) new cables go in conduit, sloped to drain out
any water, 2) the MFJ-259B (sans terminator, etc) does a fine job
indicating the proper dimensions of 75Z phasing lines.
73 bill n4lg
At 11:32 AM 8/14/2007, you wrote:
>Hi,
>
>I want to cut lambda/4 phasing lines (RG-11 foam) for some
>4-Squares using
>hybrid couplers and have the following question ...
>
>In the past I did cut some 50 Ohm phasing lines with a signal
>generator
>going to a T-connector, one side of the T going to a precision
>wattmeter
>(with internal 50 Ohm load) and the phasing line (open at the end)
>went to
>the other side of the T. With this set up it was very easy to cut
>the cable
>to the desired length (minimum power in the load).
>
>Can I use the same set-up to cut 75 Ohm lines or would it be
>necessary to
>use a 75 Ohm load?
>
>How big is the error if a networkanalyser (with 50 Ohm input) is
>used to cut
>the length?
>
>Thanks for any insight ;-)
>
>73ss
>
>Carsten, DL6LAU
>
>_______________________________________________
>
>
>... maybe I found the answer myself after writing the mail and
>thinking it
>over ;-) ...
>
>Could it be that the set-up with the T-connector is independent of
>the used
>impedance of the cable because it will create a short at the T
>when the
>lamba/4 lenght of the line is found??
>
>Please correct me if I am wrong (or say yes you are right ;-).
>
>Thanks!
>
>Carsten
>
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
----------------------------------------------------------
Bill Cotter, N4LG E-mail: n4alg@qx.net
173 Carolyn Lane Home: (859) 887-5563
Nicholasville, KY 40356-9340 Work: (859) 323-6474
ARRL ARCI #9878 QRPl #1646 QCWA #29393 FISTS #4535
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