[amsat-bb] Circular switching techniques

Frank Woolfe frankwoolfe at optusnet.com.au
Thu Jun 25 15:44:19 PDT 2009


All, has anybody had any real success with the switching method described in
the ARRL Antenna Handbook using one coaxial relay and a length of 93 ohm
line to switch from LHCP to RHCP on crossed yagi’s?  I have tried this
method several times and there appears to be very little difference in
signal level. I seem to think that the 93 ohm cable is close enough to 75ohm
and becomes a transformer instead of the delay line that the idea is trying
to achieve. I also seem to think that for this idea to work properly that
the delay line impedance should be in the vicinity of 110-125 ohms. I have
seen many methods using two relays, and yes that would have to be the surest
method of accomplishing this. However, for ease of construction I like the
single relay method. I have constructed these to the letter using only one
velocity compensated ¼ wave length of coax on the 75ohm transformers and on
the delay line, that’s were I thinking that the transformer sections and
delay lines should perhaps be long odd multiple of a ¼ wave length, i.e.;
3/4 , 5/4 etc to see a better impedance match. Any ideas from past
experience would be appreciated.

Best 73’s Frank VK5KV

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