[amsat-bb] Req. help with making a Coax Hybrid

Joop & Tineke Verdoes joop.verdoes at nameplanet.com
Fri Nov 17 04:06:36 PST 2006

I am at the moment attempting to make a 2m and a 70cm Coax hybrid
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
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

More information about the AMSAT-BB mailing list