My guess is that the single stub test is rather broad compared to the full hybrid where there might be a a multiplying effect of any small differences. So being slightly short wouldn't show up in the single leg test? I'd be interested in hearing what you end up with... Bob
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Joop & Tineke
Verdoes
Sent: Friday, November 17, 2006 7:07 AM To: [email protected] Subject: [amsat-bb] Req. help with making a Coax Hybrid
OM's I am at the moment attempting to make a 2m and a 70cm Coax
hybrid
divider/combiner. I get interesting results. I have made 3 1/4 and 1 3/4 lamda pieces of 75 Ohm coax.
- I included the velocity factor (after measuring this)
- I tested each by using them as a 1/4 or 3/4 impedance
tranformer 100
Ohm to 50 Ohm, my MFJ 269 sees each of the pieces terminated
with 100
Ohm, nicely as a 50 Ohm thing, right on the frequency I want
(146 MHz)
I solder the 4 pieces into a ring, terminate with 50 Ohm at 3 ports and connect the MFJ at the "TRX" port. The thing works (ie shows 50 Ohm with and swr of
1.0).........but at
166MHz. At 145Mhz, the swr is 1.2 and the impedance shows some reactance. Before attempting to make wild guesses which leg of the hybrid
I am
going to cut/extend, would like to ask whether there is someone who can point me in the right direction. The coax cable is 3c-2v tv 75Ohm coax. It appears that the pieces are a bit too short, but this
doesn't agree
with my test of each leg seperately as an impendance
transformer.
Any suggestions?
Joop, PA1JAV
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