On 8/30/2010 3:48 PM, Paul Plack wrote:
I'm working on a UHF ham repeater project for installation some time next year, and was getting set to build one based on 35-watt Mitreks. I've just been offered a 100-watt Mastr II UHF repeater, complete including the cabinet, just taken out of service in a switch to narrow-band equipment. I helped maintain a VHF Mastr II repeater for a club years ago, and once built a UHF repeater out of a converted mobile, so I know the beast a bit, but have two questions... I don't know the current frequency, but suspect it's in the 460/465 MHz range. Will it move down into the 440s without a lot of grief?
Yup yup yup. Never seen one that didn't, except one that had a dead stage in the receiver, which uhh... made it kinda deaf.
;-)
Also, I don't need anywhere near 100 watts, and need to avoid abusing the good nature and power bill of my landlord. (Also hope to have battery backup.) Can the 100-watt UHF PA be jumpered from an intermediate stage to the filter, bypassing the final? I seem to recall these would run at something in the 10-25-watt range with such a mod.
Driver board is 40W and on the UHF, it's easy to jumper out (or remove) the final board. VHF, due to having feedback circuitry for RF power control, is a different story. But UHF is a piece of cake.
Or, is this just gross overkill for a local repeater, and the Mitrek-based idea more appropriate?
They're bulky, but you can't find anything on the market that will outperform them today for SELECTIVITY.
You may want a pre-amp on the receiver for SENSITIVITY, depending on other factors of your antenna system and site selection and how far out you want it to hear.
You can start whole religious debates about WHICH pre-amplification system to use on them, here on RB. It can get quite entertaining. But they do work better with the RIGHT filtering and pre-amplification on the receive side of things.
Now, where's my hand truck...
LOL... we spent Sunday moving four MASTR II stations, two power supplies, 7 PAs, and boxes full of spare parts into the pickup truck of another person in the club who has more room for WORKING on all of it, than I did. I love MASTR II's, but I have learned to HATE storing them. :-)
Other comments: When you get the station, post photos or look through the LBIs and see what (hopefully factory) configuration it's in. Some were repeaters, some were just "stations" (remote base, tone-remote, etc) but all can easily be reconfigured to repeater operation.
If the PA has a T/R relay on it, you have to deal with that, and there's some articles here on how to do it... personally I just rip the T/R relay off the board completely and bypass the RF on over to the original RCA connector via a VERY short jumper. Others do other things.
If it doesn't have a T/R relay on it, you might find that it has a Z-matcher that needs to be tuned. You can start large religious debates about how to do that properly here, too. Some folks disagree with the manufacturer's very simplistic tuning instructions. Your decision.
A "real" repeater will have certain cards in the card shelf up on top. You have lots of options there... use the cards, rip out the cards and wire in an off-board controller, use the controller one manufacturer makes that slides into a card slot... etc.
And there's other stuff... the tone boards (separate for exciter/TX and receiver/RX in a "normal" MASTR II station/repeater), may or may not be present... etc.
A photo or three and/or the "combination number" are worth a thousand words...
Post a couple photos of your new pride and joy, and we'll help you figure out which configuration it looks like it's in. The LBI's are also REQUIRED reading, after you've had a visual "tour" of the station.
They're solid, solid, solid radios. Only thing I've come to learn to hate are the 110W VHF PAs. UHF, 100W and 75W are solid, radios are solid.
Only other "odd" thing I ever saw happen to one of them *ever*, was the tone board worked it's way UP off of the pins in a station once, and keyed it continuously... a little double-sided foam tape above the tone board in the covers, takes care of that... if you're even worried about it. Happened once in a decade... to only one station...
Anyway... you learn to love 'em and decide that the weight and bulk is worth it... :-)
-- Nate Duehr, WY0X
