[amsat-bb] Re; Circular switching
frankwoolfe at optusnet.com.au
Fri Jun 26 16:42:56 PDT 2009
Hi Jan PE0SAT, my emails are not getting through to you so I'll post here,
I have had some success so far,
I've made up two lengths of RG213 with 1/4 wave lengths of 75ohm cable on
each end. These are to run from the coax relay to the 145mhz Yagi's as the
ARRL drawing suggests. N type connectors are used on each end of these
I've tested this as a phasing harness and achieved around 30dB return loss
that's with the 75ohm transformer ends in a T piece and 50ohm loads on the
end of each cable.
This was tested on my HP8920 using a 50Mhz to 1000Mhz Narda coupler and am
happy with the results, so the phasing harness as it is, is centered on
145mhz with a VSWR of 1.06:1.
Next is the delay line, this has got to be an impedance of between 104 to
110ohms, as the antennas are between 52 to 55ohms now this is going to be
hit and miss, as you can't get 105ohm coax. However, you can get 93ohm and
what I'm thinking is to remove the center conductor of the coax and replace
it with a smaller diameter conductor this should raise the impedance of the
coax hopefully to around 105-110 ohms, thus achieving the required impedance
of the delay line which is called for in that circuit.
The 93 ohms is just too low and I've found with my testing so far it's
better to be on the high side of impedance than the low. The 93 ohms seems
to look like near enough to 75ohms and acts like another transformer
So I'll continue on and keep you in the loop on success or failure.
Thanks for your mail and Best 73's
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