Isn't the rpt. going to be built using (2) Mitrex, thus shielding should not be a problem. I have, in the past (with the help of a Bridgeport mill), fashioned "Larger Heatsinks", that bolt onto the orig. Mitrex heat sink....seems to dissipate heat well.
I have an MSR-2000 (100w) rpt. that has been in service 15 yrs w/o a problem......really like the "Mitrex" design, and easy to replace discrete components, if need be! With two separate radios, controller and duplexers....you are off and running! Best Regards, Tim W7TRH Vashon Is. Wa. ----- Original Message ----- From: "Jack Taylor" <[email protected]> To: [email protected] Sent: Monday, April 26, 2010 8:27:44 AM GMT -08:00 US/Canada Pacific Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? I converted a UHF Mitrek for full duplex packet operation once. Don't recommend it because the Mitrek rx and tx are on a single board which results in transmit chain spurs and harmonics getting into the rx. The task required a spectrum analyzer and several hours experimenting with various shielding and filtering techniques to get the rx desense down to a reasonable level. 73 de Jack - N7OO ----- Original Message ----- From: Tony KT9AC To: [email protected] Sent: Monday, April 26, 2010 8:09 AM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? Good question Paul. Remember the Mitrek RF decks are almost the same used in the MSR2000 repeater, and with their tuned helical front end make great receivers. For the transmitter however, I would not run it on its own. Also reducing the power output below 50-66% of rating might cause spurious issues. The best is to get a manual and bypass the PA, running driver power only. Then use an external amp to get your power up to where you need it. This is how every Micor, MSR, MSF repeater is designed. Motorola typically spec'd transmitters at 70.7% to get the best balance from the parts, and typically used multiple stages to get there (i.e. 200mW-2W-15W-50W). I recently picked up two 50W Mitrek Plus models that I will be using for linking duty, and will be bypassing the PA on those as well. At only 10 miles driver power only should work, but I have yet to complete that phase. Good luck on your project! You'll never know what duty cycle is needed during an event, so better to overprepare than worry. Tony On 04/26/2010 01:47 AM, Paul Plack wrote: After a few years on the sidelines, it looks as if I'm going to be jumping back into repeater ownership. I have a few nice pieces left from my last adventure, including a TX/RX duplexer and a loaded S-COM 7K, but I'm pondering choices in RF decks. This will be a local UHF machine designated as an asset for a emergency net in a suburban area, at a modest height, and the only RF device at its site. I have two Mitrek 30w UHF mobile radios, and am aware of their duty-cycle limitations, but would like to consider using them. They have channel elements, and I'm not averse to spending the money to have the elements redone properly. Looks like the pair will be 447.xx transmit / 442.xx receive. I have a couple specific questions about these radios... (1) If Mitreks are converted for full duplex, how well do they work? I'd like to have a complete, swappable RF setup, so trips to the site are short, and repairs can be done on my bench at home. (As opposed to requiring the two radios as separate receiver and transmitter.) (2) Would it be a reasonable pursuit to adapt a larger heatsink, and would that safely allow 100% duty cycle at 25-30 watts? (I'm philosophically opposed to fans which introduce the opportunity for a bearing to take the machine out of service.) (3) Any comments on the front ends? (4) I know these lack the sophistication of the Micor mobiles. Is the lack of a circulator a big deal in this application, at an isolated site with no other transmitters? (5) Was Motorola's quality in the Mitrek era still good enough to make a Mitrek preferred over, say, synthesized commercial transmitter boards from lesser manufacturers, but of more current vintage? All comments welcome. 73, Paul, AE4KR
