I duplexed a 75 W UHF Mitrek (not Mitrex...) nearly 15 years ago now. It's still running fine, no in-cabinet desense. I have it running at abt 40-45W out with a fan on it (same fan for all that time too, btw). Only issue is the power control pots seem a little flaky sometimes and don't allow power out, but it doesn't happen often. I could see desense being a problem on VHF and especially low-band, though...
On 4/26/2010 2:11 PM, Jeff DePolo wrote: > > Because of the internal desense issue, I'd build them the same, but operate > the two radios separately. That is, use one as a transmitter and the other > as the receiver by default. No duplex mods required. If the Tx dies on > one, swap the system cables around to make the formerly-transmitter radio > the receiver, and vice-versa. You could even automate the changeover via a > couple of coaxial relays and some simple homebrew transistor and/or relay > logic tied into your controller. > > --- Jeff WN3A > > >> -----Original Message----- >> From: Repeater-Builder@yahoogroups.com >> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Paul Plack >> Sent: Monday, April 26, 2010 1:49 PM >> To: Repeater-Builder@yahoogroups.com >> Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? >> >> >> >> ? >> Tim, >> >> My plan at this point is to convert them to full duplex, so I >> can use the second Mitrek to prepare a complete, plug-in, >> standby set of RF decks. The mods look very straightforward, >> but I was wondering if there were any gremlins people discovered. >> >> Your heatsink approach, however, is exactly what I was >> talking about. I have several very large heatsinks originally >> designed for use with big SCR switching circuits which look >> to be more than generous for a 30w PA at 100% duty cycle. >> >> My first repeater was built from a 2w Repco exciter board >> repurposed from RFID service. It was supposedly rated for >> continuous duty, but had to run very hot to dump the heat it >> produced through the little aluminum tab mounted to its own >> PC board within the case. I fashioned a new tab with a 90ยบ >> twist which allows sinking the little PA to the case itself, >> and it never got above "warm to the touch," even after hours key-down. >> >> Guys, I appreciate all the input. >> >> 73, >> Paul, AE4KR
