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

Robert Bruninga bruninga at usna.edu
Fri Nov 17 05:35:10 PST 2006

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: amsat-bb-bounces at amsat.org 
> [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Joop & Tineke
> Sent: Friday, November 17, 2006 7:07 AM
> To: amsat-bb at amsat.org
> 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
> 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
> Any suggestions?
> Joop, PA1JAV
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