Is there any concensus as to how much power a Maxtrac repeater can safely run, whether D27 or D37?
Jeff
Maxtrac - Continuous Duty Rating?
Moderator: Queue Moderator
I used to run D34 and D44 MaxTracs on a UHF repeater. I tried rated power, half rated power, and about 1/3rd rated power. They get hot, very hot, no matter what amount of power they're making. A fan moving lots of air over the heatsink helps a lot. I eventually ended up with a D34 (25w radio) running about 7 watts into an outboard power amp. The radio stays cool, but the algorithm inside still thinks it should be getting hot after 45-60 minutes of continuous transmitting. Some radios shut down sooner. This is with the transmit timeout set to 000. You can't set the power too low because the transmitters start putting out spurious emissions.
The 900 MHz MaxTracs use an RF power amp module that's supposed to be good for 18-20 watts. The 30w radio follows this with a single transistor to bump the power by 3-6dB. All the components are well mounted to the heatsink, but the radios are still not rated for continuous duty. I wouldn't run the radio at anything higher than their rated power: 12 or 30 watts. By the way, the D37 is rated for 30 watts on 896-902 MHz but only 20 watts on 935-941 MHz, so for amateur repeater use, you don't want to go over about 20 watts.
I had a D27 on my 900 MHz repeater and when set to 12 watts with a fan blowing on it, it stays comfortable. Your mileage will vary. Even at that power setting, the radios draw about 4.5 amps at 14 volts, so you have to get rid of an awful lot of heat (about 45-50 watts-worth). I just switched to a 300 watt continuous-duty Nucleus transmitter, and that has plenty of air flow and heatsink fins and does NOT get hot, especially when running at 130 watts.
Bob M.
The 900 MHz MaxTracs use an RF power amp module that's supposed to be good for 18-20 watts. The 30w radio follows this with a single transistor to bump the power by 3-6dB. All the components are well mounted to the heatsink, but the radios are still not rated for continuous duty. I wouldn't run the radio at anything higher than their rated power: 12 or 30 watts. By the way, the D37 is rated for 30 watts on 896-902 MHz but only 20 watts on 935-941 MHz, so for amateur repeater use, you don't want to go over about 20 watts.
I had a D27 on my 900 MHz repeater and when set to 12 watts with a fan blowing on it, it stays comfortable. Your mileage will vary. Even at that power setting, the radios draw about 4.5 amps at 14 volts, so you have to get rid of an awful lot of heat (about 45-50 watts-worth). I just switched to a 300 watt continuous-duty Nucleus transmitter, and that has plenty of air flow and heatsink fins and does NOT get hot, especially when running at 130 watts.
Bob M.
Power control
Bob, did you use the hardware power control mod on those radios, or did you find it unnecessary?
As to the alternate PA question, I don't know what they're doing with the unloved Nuclii out here, but I'd be happy to haul one away from somewhere and put it to use.
The actual Plan B is to run an 800 MHz Micor, already obtained. However, it's clear that the Maxtracs will be on the air much sooner!
'JK
As to the alternate PA question, I don't know what they're doing with the unloved Nuclii out here, but I'd be happy to haul one away from somewhere and put it to use.
The actual Plan B is to run an 800 MHz Micor, already obtained. However, it's clear that the Maxtracs will be on the air much sooner!
'JK
Yes, I had to use manual power control. The one I was given would put out 19-20 watts on frequencies in the 927-928 MHz range. In fact, the one I'm using was the basis for an article about manual power control over on repeater-builder.com.
The MaxTracs are a quick and dirty way to get something on the air, and with a big (4-3/4 inch) fan keeping it cool, it seems to run quite nicely.
Now that I've increased my transmitter power by a factor of 10, the repeater has a mouth that's bigger than its ears, even with a preamp on the receiver. There's just too much other stuff around 902 MHz that kills weak signals. A GTX portable (about 3 watts) might be noisy getting into the repeater, but it hears the repeater solidly.
I also have some TOKO 915 MHz filters that replace the ones in the 800 MHz MaxTracs, should you want to convert one to be a 900 MHz receiver. No reason to waste a 900 MHz MaxTrac unless you want to run HearClear on the repeater. These are a lot cheaper to find, and they work great, even though they're wide-band (as compared to a 900 MHz radio).
Bob M.
The MaxTracs are a quick and dirty way to get something on the air, and with a big (4-3/4 inch) fan keeping it cool, it seems to run quite nicely.
Now that I've increased my transmitter power by a factor of 10, the repeater has a mouth that's bigger than its ears, even with a preamp on the receiver. There's just too much other stuff around 902 MHz that kills weak signals. A GTX portable (about 3 watts) might be noisy getting into the repeater, but it hears the repeater solidly.
I also have some TOKO 915 MHz filters that replace the ones in the 800 MHz MaxTracs, should you want to convert one to be a 900 MHz receiver. No reason to waste a 900 MHz MaxTrac unless you want to run HearClear on the repeater. These are a lot cheaper to find, and they work great, even though they're wide-band (as compared to a 900 MHz radio).
Bob M.
11K0
I do want to experiment with HearClear. In fact, if one of these radios has problems, I'm thinking about trying its module in the Micor instead of trying to fix it.
I'm thinking the 800 radios are better suited to user use anyway. The band is supposedly filling up out here, and the coordinator requires us to observe the 11K0 emission standard, so it's desirable to have a receiver appropriate to that standard. This way, users running excess deviation will be more likely to fix it. I'm sure things are looser elsewhere, but this is the world I'm working in.
I'm thinking the 800 radios are better suited to user use anyway. The band is supposedly filling up out here, and the coordinator requires us to observe the 11K0 emission standard, so it's desirable to have a receiver appropriate to that standard. This way, users running excess deviation will be more likely to fix it. I'm sure things are looser elsewhere, but this is the world I'm working in.
Yup, that's about all you can do for now, until someone figures out how to disable the shutdown algorithm inside the radio.
Once it thinks it's hot enough and shuts off the output power, you can get maybe a minute of transmitting after the PTT line shuts off (i.e. the repeater controller releases it). Several seconds of dead time gets you minutes of transmitting time. It's still a royal P.I.T.A. but until you get something better, all you can do is live with it.
Eventually I obtained an MSF5000 station and turned it into a repeater. No more timeouts, plus it's rated for continuous duty cycle. I added a fan to it just to stir up the air.
Bob M.
Once it thinks it's hot enough and shuts off the output power, you can get maybe a minute of transmitting after the PTT line shuts off (i.e. the repeater controller releases it). Several seconds of dead time gets you minutes of transmitting time. It's still a royal P.I.T.A. but until you get something better, all you can do is live with it.
Eventually I obtained an MSF5000 station and turned it into a repeater. No more timeouts, plus it's rated for continuous duty cycle. I added a fan to it just to stir up the air.
Bob M.
ah so the radio just thinks its getting too hot... hrmm, i wonder how effective it would be to just make a circuit to unkey the radio for 1/100th of second every min or if something like that would be enough to trick it into being happy?W6JK wrote:That's a nice way to make lots o' watts, but it doesn't keep the Maxtrac from shutting down when it thinks it must be too hot.
how long does it take for the radio to think its over heating?
45-60 minutes of continuous transmitting. My repeaters have a courtesy beep 1 second after loss of input carrier, and a transmitter hang time of 5 seconds after that, so with a good technical QSO going on during drive time, we can get 45 minutes of transmitter ON-time.
I did have a fan blowing on the power amp, and the radio was running at around 7 watts output and was ice cold.
Bob M.
I did have a fan blowing on the power amp, and the radio was running at around 7 watts output and was ice cold.
Bob M.