[TowerTalk] How to cut 75 Ohm lambda/4 phasing lines (with 50 Ohm testequipment)?

Carsten Esch carsten.esch at appello.de
Tue Aug 14 11:32:06 EDT 2007


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 ;-)


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 ;-).



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