Re: [Repeater-Builder] Mitreks as UHF Repeaters?
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 90º 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
[Repeater-Builder] Mitreks as UHF Repeaters?
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
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
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
I've used a lot of Mitreks as repeaters and loved them, but you're right about the PA -- if you don't like fans, it's going to get too hot. Consider getting the exciter output after the helical filters and use a different PA. I have a couple of Mitreks stashed in a corner somewhere just in case -- I've moved on to newer synthesized stuff, but I know in a pinch I can have one up and running as a repeater with a couple hours of work. On Apr 26, 2010, at 1:47 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 -- Cort Buffington H: +1-785-838-3034 M: +1-785-865-7206 Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * Your email settings: Individual Email | Traditional * To change settings online go to: http://groups.yahoo.com/group/Repeater-Builder/join (Yahoo! ID required) * To change settings via email: repeater-builder-dig...@yahoogroups.com repeater-builder-fullfeatu...@yahoogroups.com * To unsubscribe from this group, send an email to: repeater-builder-unsubscr...@yahoogroups.com * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
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: Repeater-Builder@yahoogroups.com 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 --
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
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 sinkseems 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 duplexersyou are off and running! Best Regards, Tim W7TRH Vashon Is. Wa. - Original Message - From: Jack Taylor j...@n7oo.com To: Repeater-Builder@yahoogroups.com 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: Repeater-Builder@yahoogroups.com 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
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 90º 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 - Original Message - From: w7...@comcast.net To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 10:16 AM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? 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 sinkseems to dissipate heat well...
RE: [Repeater-Builder] Mitreks as UHF Repeaters?
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 90º 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 - Original Message - From: w7...@comcast.net mailto:w7...@comcast.net To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 10:16 AM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? 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 sinkseems to dissipate heat well... No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.801 / Virus Database: 271.1.1/2792 - Release Date: 04/26/10 02:31:00
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
At 10:49 AM 4/26/2010, Paul Plack wrote: 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. Remember folks that heatsink capability is not the only issue when it comes to duty cycle. Components such as caps, resistors, diodes and even pc board traces all factor in as well and, even though you might be able to suck the heat away from the transistors adequately, other parts aren't necessarily up to the task and could very well fail. Ken -- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcontrollers.com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp.net We don't just make 'em. We use 'em!
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
On Mon, 26 Apr 2010, Paul Plack wrote: 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 90? 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 Remember, the 100W Mitrek had a heatsink that was rated for 35W and used the duty cycle to keep things cool. If you do a case swap from a 30W radio into a 100W case, you could be fine for 100%, barring excessive temperature climb. My druthers would be to use an Original Syntor. It's got the helicals of a Mitrek, and the programming of a PROM. At $10 per frequency change (the going rate of the PROM chip), it's still cheaper than the Mitrek and uses the Mitrek/Motrac accessories. -- Kris Kirby, KE4AHR Disinformation Analyst
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
Paul, Using one Chassis for full duplex may cause some problems, as mentioned in an earlier post! More than likely, you should be able to find many Mitrek radios for next to nothing. This way, you will be able to run separate rec. and xmitter, thus you won't have to worry too much about shielding or by-passing. (The difference is apparent, when looking at a MSR2000 base and MSR2000 rpt. The rpt. has much by-passing, yet uses the same boards for rec. and exciter.) I ran seperate Mitrek radios for several years for AirForce MARS without any particular problems. That is the machine that I used the large heatsink with. I would recommend using seperate rec. and xmitters. Regards, Tim Hardy W7TRH/AFA0TP Vashon Is. Wa. - Original Message - From: Paul Plack pl...@xmission.com To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 10:49:00 AM GMT -08:00 US/Canada Pacific 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 90º 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 - Original Message - From: w7...@comcast.net To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 10:16 AM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? 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 sinkseems to dissipate heat well...
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
Ken, Correct, of course, but I'm assuming that in a 30w PA, smaller components not somehow directly sunk to the main chassis heatsink will reach their max operating temps in a very few seconds of key-down, and therefore have to be spec'd the same for intermittent duty PAs as if they would if they were in continuous duty. I'm willing to roll those dice, especially if a similar design was used by the manufacturer in repeater service. There seem to be plenty of Mitreks used as repeaters in the past, so I think we'll be OK. I'm gathering, however, that as cheap as these radios have become, it mike just make sense to use two radios, and source more spares. 73, Paul, AE4KR - Original Message - From: Ken Arck To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 12:01 PM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? At 10:49 AM 4/26/2010, Paul Plack wrote: 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. Remember folks that heatsink capability is not the only issue when it comes to duty cycle. Components such as caps, resistors, diodes and even pc board traces all factor in as well and, even though you might be able to suck the heat away from the transistors adequately, other parts aren't necessarily up to the task and could very well fail. Ken -- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcontrollers.com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp.net We don't just make 'em. We use 'em!
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
Kris, looking at the pictures of the Mitreks of various power levels, I'm not confident there would be holes and heatsink pads in the high-power case that line up with the board mounts and needed contact points of the low-power PA board. But yes - I had considered that approach. I am completely unfamiliar with the Syntor, cost, availability, etc., but I'm also early in the process of nosing around locally. I'm willing to look at any plentiful, high-quality radios for the conversion. 73, Paul, AE4KR - Original Message - From: Kris Kirby To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 12:26 PM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? On Mon, 26 Apr 2010, Paul Plack wrote: Remember, the 100W Mitrek had a heatsink that was rated for 35W and used the duty cycle to keep things cool. If you do a case swap from a 30W radio into a 100W case, you could be fine for 100%, barring excessive temperature climb. My druthers would be to use an Original Syntor. It's got the helicals of a Mitrek, and the programming of a PROM. At $10 per frequency change (the going rate of the PROM chip), it's still cheaper than the Mitrek and uses the Mitrek/Motrac accessories. -- Kris Kirby, KE4AHR Disinformation Analyst
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
Jeff, I appreciate the thoughts. Anytime I've looked at a scheme which allows simply swapping the TX and RX to get back on the air, I arrive at the same conclusions... (1) If I took a lightning hit at the site, I'd want my spares to have been stored somewhere else. (2) Once I swap the TX and RX, I still can't bring either home for repair without taking the machine off the air. As far as the automated switchover, the 7K has three receiver and two transmitter ports, so I wouldn't even need coax relays to provide remote swap capabilities. I could just crystal each radio for simplex, wire both receivers and both transmitters into the controller, issue a remote DTMF command to swap them, and instantly implement a second repeater on the upside-down split. I think my answer is going to end up being building a stash of spares, and using two radios. 73, Paul, AE4KR - Original Message - From: Jeff DePolo To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 12:11 PM Subject: RE: [Repeater-Builder] Mitreks as UHF Repeaters? 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 90º 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 - Original Message - From: w7...@comcast.net mailto:w7...@comcast.net To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 10:16 AM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? 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 sinkseems to dissipate heat well... No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.801 / Virus Database: 271.1.1/2792 - Release Date: 04/26/10 02:31:00
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
At 11:47 AM 4/26/2010, Paul Plack wrote: Ken, Correct, of course, but I'm assuming that in a 30w PA, smaller components not somehow directly sunk to the main chassis heatsink will reach their max operating temps in a very few seconds of key-down, and therefore have to be spec'd the same for intermittent duty PAs as if they would if they were in continuous duty. ---There are several components that are common failures in Mitreks used in duty cycle apps greater than it was designed for. One should read the following: www.ecso.com/srca/modmitrek_files/mitrex_mod.pdf Just sayin' -- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcontrollers.com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp.net We don't just make 'em. We use 'em!
RE: [Repeater-Builder] Mitreks as UHF Repeaters?
I appreciate the thoughts. Anytime I've looked at a scheme which allows simply swapping the TX and RX to get back on the air, I arrive at the same conclusions... (1) If I took a lightning hit at the site, I'd want my spares to have been stored somewhere else. (2) Once I swap the TX and RX, I still can't bring either home for repair without taking the machine off the air. Understood. As far as the automated switchover, the 7K has three receiver and two transmitter ports, so I wouldn't even need coax relays to provide remote swap capabilities. I could just crystal each radio for simplex, wire both receivers and both transmitters into the controller, issue a remote DTMF command to swap them, and instantly implement a second repeater on the upside-down split. Yikes, upside-down? Your co-channel neighbors will just love that! I think my answer is going to end up being building a stash of spares, and using two radios. Yeah, I'd definately go with split radios however you end up doing it. If you're going to assume you're going to make the trip to the site in the event of a failure, then there's probably no need to order two sets of crystals, just move the elements when you swap radios and net them on frequency. These days, the cost of crystals is usually more than the cost of the radio they're going into...which is why I've mostly gone synthesized. --- Jeff WN3A
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
Ken, Thanks, appreciate the link. This document adds a few details to what I had on hand. Good to know the high-split Mitreks weren't prone to the spurs when duplexed. Also encouraging to read that the 30w radios will run 100% at 20w with the smaller heatsink. That's probably all the power I'd need in my application. 73, Paul, AE4KR - Original Message - From: Ken Arck To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 1:09 PM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? At 11:47 AM 4/26/2010, Paul Plack wrote: Ken, Correct, of course, but I'm assuming that in a 30w PA, smaller components not somehow directly sunk to the main chassis heatsink will reach their max operating temps in a very few seconds of key-down, and therefore have to be spec'd the same for intermittent duty PAs as if they would if they were in continuous duty. ---There are several components that are common failures in Mitreks used in duty cycle apps greater than it was designed for. One should read the following: www.ecso.com/srca/modmitrek _files/mitrex_mod.pdf Just sayin' -- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcontrollers.com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp.net We don't just make 'em. We use 'em!
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
On Mon, 26 Apr 2010, Paul Plack wrote: I am completely unfamiliar with the Syntor, cost, availability, etc., but I'm also early in the process of nosing around locally. I'm willing to look at any plentiful, high-quality radios for the conversion. 73, Paul, AE4KR Syntor -- not Syntor X or Syntor X9000 -- has the helicals of the Mitrek and excellent suppression of other nearby signals. The radio is only about 2MHz wide at widest tuning. Every other Motorola radio beyond them is 22-28MHz wide. -- Kris Kirby, KE4AHR Disinformation Analyst
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
I ran a Duplexed 50W UHF mitrek @30W with a Fan on the heat sink for 5 years without a problem. I Upgraded that site to a full blown UHF Micor Repeater that is 75W. As expected on the TX the range is better, but the Micor is also a slight bit better on the RX as well. I will probably re-use the mitrek radio in a future RX site since I have it and the channel element. That being said, the Mitrek served me well and was a great way to get the repeater going. If I did Mitreks again I would use two radios, not because I had any problems, but because of the redundancy it would offer. TX or RX dies, just swap radios and your back on the air. As a side note to running a single duplexed radio, I never had any measurable de-sense, but I did get spurrs and crap when I tried setting the TX power too low. Its happiest at 50-75% of its rated power. Tom W9SRV --- On Mon, 4/26/10, Paul Plack pl...@xmission.com wrote: From: Paul Plack pl...@xmission.com Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? To: Repeater-Builder@yahoogroups.com Date: Monday, April 26, 2010, 3:07 PM Ken, Thanks, appreciate the link. This document adds a few details to what I had on hand. Good to know the high-split Mitreks weren't prone to the spurs when duplexed. Also encouraging to read that the 30w radios will run 100% at 20w with the smaller heatsink. That's probably all the power I'd need in my application. 73, Paul, AE4KR - Original Message - From: Ken Arck To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 1:09 PM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? At 11:47 AM 4/26/2010, Paul Plack wrote: Ken, Correct, of course, but I'm assuming that in a 30w PA, smaller components not somehow directly sunk to the main chassis heatsink will reach their max operating temps in a very few seconds of key-down, and therefore have to be spec'd the same for intermittent duty PAs as if they would if they were in continuous duty. ---There are several components that are common failures in Mitreks used in duty cycle apps greater than it was designed for. One should read the following: www.ecso.com/ srca/modmitrek _files/mitrex_ mod.pdf Just sayin' - - - - - - - --- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcon trollers. com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp. net We don't just make 'em. We use 'em!
Re: [Repeater-Builder] Mitreks as UHF Repeaters?
Tom, Yes - the spurs mentioned were not the ones created by running the power too low. Apparently, the 406-420 Mitreks had a separate issue which was not dependent on power setting, in which the local oscillator for the receiver would get into the exciter's multiplier chain. I think almost any of these discreet-component PAs wander off the spec chart if you run them too far below rated power. My last UHF repeater was a 35w Mastr II, and it started getting pretty gritty below about 18 watts. 73, Paul, AE4KR - Original Message - From: TGundo 2003 To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 3:26 PM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? I ran a Duplexed 50W UHF mitrek @30W with a Fan on the heat sink for 5 years without a problem. I Upgraded that site to a full blown UHF Micor Repeater that is 75W. As expected on the TX the range is better, but the Micor is also a slight bit better on the RX as well. I will probably re-use the mitrek radio in a future RX site since I have it and the channel element. That being said, the Mitrek served me well and was a great way to get the repeater going. If I did Mitreks again I would use two radios, not because I had any problems, but because of the redundancy it would offer. TX or RX dies, just swap radios and your back on the air. As a side note to running a single duplexed radio, I never had any measurable de-sense, but I did get spurrs and crap when I tried setting the TX power too low. Its happiest at 50-75% of its rated power. Tom W9SRV --- On Mon, 4/26/10, Paul Plack pl...@xmission.com wrote: From: Paul Plack pl...@xmission.com Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? To: Repeater-Builder@yahoogroups.com Date: Monday, April 26, 2010, 3:07 PM Ken, Thanks, appreciate the link. This document adds a few details to what I had on hand. Good to know the high-split Mitreks weren't prone to the spurs when duplexed. Also encouraging to read that the 30w radios will run 100% at 20w with the smaller heatsink. That's probably all the power I'd need in my application. 73, Paul, AE4KR - Original Message - From: Ken Arck To: Repeater-Builder@yahoogroups.com Sent: Monday, April 26, 2010 1:09 PM Subject: Re: [Repeater-Builder] Mitreks as UHF Repeaters? At 11:47 AM 4/26/2010, Paul Plack wrote: Ken, Correct, of course, but I'm assuming that in a 30w PA, smaller components not somehow directly sunk to the main chassis heatsink will reach their max operating temps in a very few seconds of key-down, and therefore have to be spec'd the same for intermittent duty PAs as if they would if they were in continuous duty. ---There are several components that are common failures in Mitreks used in duty cycle apps greater than it was designed for. One should read the following: www.ecso.com/ srca/modmitrek _files/mitrex_ mod.pdf Just sayin' - - - - - - - --- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcon trollers. com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp. net We don't just make 'em. We use 'em!
[Repeater-Builder] Mitreks
How does one tell the differance between a High Low power and VHF or UHF Mitrek? Thankyou
RE: [Repeater-Builder] Mitreks
Randy, A low-power Mitrek chassis has fins that are about 1/2 deep, while the high-power units have fins that are about 1-1/2 deep. A VHF high-band radio (150-174 MHz) will have a 3 as the third character in the model number, as in T43JJA6900DK. A UHF radio will have a 4 in the same location. A low-band (30-50 MHz) Mitrek will have a 1 in that location. Be aware that some Mitrek models come in more than just two power levels. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Randy Sent: Wednesday, October 08, 2008 8:28 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Mitreks How does one tell the differance between a High Low power and VHF or UHF Mitrek? Thankyou
Re: [Repeater-Builder] Mitreks
Jim, I you have trouble getting rid of a couple of VHF high band Mitreks I will pay shipping. Collin -Original Message- From: Jim, K8COP [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sat, 6 Sep 2008 4:20 pm Subject: [Repeater-Builder] Mitreks I have a stack of UHF/VHF/Lo Band Mitreks. There is some cables, etc with them. Free for pick up ONLY. Located near Muskegon, MI. E-mail me direct [EMAIL PROTECTED] Jim, K8COP
Re: [Repeater-Builder] Mitreks
here too Thanks ! Gary - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sunday, September 07, 2008 11:10 AM Subject: Re: [Repeater-Builder] Mitreks Jim, I you have trouble getting rid of a couple of VHF high band Mitreks I will pay shipping. Collin -Original Message- From: Jim, K8COP [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sat, 6 Sep 2008 4:20 pm Subject: [Repeater-Builder] Mitreks I have a stack of UHF/VHF/Lo Band Mitreks. There is some cables, etc with them. Free for pick up ONLY. Located near Muskegon, MI. E-mail me direct [EMAIL PROTECTED] Jim, K8COP -- No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.169 / Virus Database: 270.6.17/1657 - Release Date: 9/6/2008 8:07 PM
Re: [Repeater-Builder] Mitreks
I would be interested if you have any hi Power UHF 50-100w. I would pay shipping etc. Ralph, W7HSG -- Original message -- From: [EMAIL PROTECTED] Jim, I you have trouble getting rid of a couple of VHF high band Mitreks I will pay shipping. Collin -Original Message- From: Jim, K8COP [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sat, 6 Sep 2008 4:20 pm Subject: [Repeater-Builder] Mitreks I have a stack of UHF/VHF/Lo Band Mitreks. There is some cables, etc with them. Free for pick up ONLY. Located near Muskegon, MI. E-mail me direct [EMAIL PROTECTED] Jim, K8COP ---BeginMessage--- ---BeginMessage--- Jim, I you have trouble getting rid of a couple of VHF high band Mitreks I will pay shipping. Collin -Original Message- From: Jim, K8COP [EMAIL PROTECTED]net To: Repeater-Builder@yahoogroups.com Sent: Sat, 6 Sep 2008 4:20 pm Subject: [Repeater-Builder] Mitreks I have a stack of UHF/VHF/Lo Band Mitreks. There is some cables, etc with them. Free for pick up ONLY. Located near Muskegon, MI. E-mail me direct [EMAIL PROTECTED] Jim, K8COP ---End Message--- ---End Message---
[Repeater-Builder] Mitreks
I have a stack of UHF/VHF/Lo Band Mitreks. There is some cables, etc with them. Free for pick up ONLY. Located near Muskegon, MI. E-mail me direct [EMAIL PROTECTED] Jim, K8COP
