> >
> > I would have interest in this also as I need to combine 443.150 and
> > 462.600 to 1 ant
> > thank you
> > Merrill
> > KG4IDD
>
> I'm just addressing the two-port project above-- would not an ordinary
> duplexer work just fine?
>
> Laryn K8TVZ
Yep, do it all the time.
When combining transmitters, you need to pay careful attention to IM
products as measured at the output of the combiner. While Part 97 is silent
on the issue of spectral purity above 225 MHz, that doesn't mean you're off
the hook if your IM products are bothering someone else. A good
"cleanliness" spec to target for IM products is they should be 43 + 10 log
(watts) down (e.g. -63 dBc for 100 watts of transmitter power). That spec
will also satisfy Part 95 GMRS for the 462.6 transmitter.
Measure the IM products at the antenna tee while both transmitters are keyed
to ensure they are adequately attenuated. A duplexer with 60 dB or so of
isolation should be more than adequate. If your transmitters already have
isolators built in (Micor, MSF, PURC, etc.), you may only need two
pass/reject cavities, one per side, to combine cleanly.
--- Jeff
