Hello all, I have a 900 MHz maxtrac that works fine in the ham band but the power keeps rolling off. It will start at about 8 watts and work it’s way down until no out put, but as soon as I un key and retransmit it will come back up to 7 watt and start the cycle over again. Any one have any thoughts on this? I am using it as a link radio and the TX is at
902,625 MHz
Thanks
Bob
900 mhz maxtrac tx power keeps rolling off?
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Power
Hi Bob,
I had the same thing with my Maxtracs I use for the low level repeaters. What happens is there is no temp sensor for the PA, so the microprocessor calculates what it thinks the PA temp is (duty cycle and power output setting). You can have a fan on the PA, and it be cold, and the radios will still back off the power, until it is all the way down to nothing.
The solution...Build a little regulator using a LM317 that gives between 0 and 9 volts using a pot for adjustment. Disconnect the "Control B+" from the PA and connect it to you regulator's output. The pot willl be your power control. You will not have software control of power nor will there be any automatic current limiting. Watch your SWR and RF out and it will be fine.
I have removed the two 56k resistors that go between the DAC and the power control circuit. This gives around 17 to 20 watts on a D37 model, and the current limitor still works, I think. Anyway, no additional circuit is needed. My 2 repeaters with Maxtracs are working fine this way.
Be sure the keep the PA cool, and it will play fine.
Josh
I had the same thing with my Maxtracs I use for the low level repeaters. What happens is there is no temp sensor for the PA, so the microprocessor calculates what it thinks the PA temp is (duty cycle and power output setting). You can have a fan on the PA, and it be cold, and the radios will still back off the power, until it is all the way down to nothing.
The solution...Build a little regulator using a LM317 that gives between 0 and 9 volts using a pot for adjustment. Disconnect the "Control B+" from the PA and connect it to you regulator's output. The pot willl be your power control. You will not have software control of power nor will there be any automatic current limiting. Watch your SWR and RF out and it will be fine.
I have removed the two 56k resistors that go between the DAC and the power control circuit. This gives around 17 to 20 watts on a D37 model, and the current limitor still works, I think. Anyway, no additional circuit is needed. My 2 repeaters with Maxtracs are working fine this way.
Be sure the keep the PA cool, and it will play fine.
Josh
I've noticed on some 800 Maxtracs if you blank the board an re-initialize and don't go thru the complete alignment (ie where you enter the xtal date etc) the will drop back in power in steps. Also Maxtracs will run "wide open" if they are out of band far enough that they are away from the alignment points.
Havn't figured out a hack for that yet, or even how wide those points are.
I suggest the previous posts fix, especially for a single freq unit....
Havn't figured out a hack for that yet, or even how wide those points are.
I suggest the previous posts fix, especially for a single freq unit....
I ran into this a while back. I found a point that I could get 9v tx. I used this and a 50 K pot to feed the op amp. I cut the trace from the two 56k chip resistors. This alows you to set the power and I will not drop back.. BUT!!! Do not set to full output and try to ragchew with it. You will until the solder melts on the final......
Walt, WB4LDS
Tucson's 900 Repeaters
902.3125 / 927.3125
DPL 606
902.8875 / 927.8875
DPL 606
IRLP Node 3045
DM 42
Walt, WB4LDS
Tucson's 900 Repeaters
902.3125 / 927.3125
DPL 606
902.8875 / 927.8875
DPL 606
IRLP Node 3045
DM 42