GM300 RF drop out

DRBsp · Post by **DRBsp** » Mon Dec 03, 2001 8:42 pm

I set the VCO for RX and TX RX is at 7.6 to 7.8 Volts the TX is about 7.6 to 7.8 or 7.9 Volts and the radios still drop off can some one email me where to put the pot in so that i can try that out
<font size=-1>[ This Message was edited by: drbsp on 2001-12-04 08:02 ]</font>

<font size=-1>[ This Message was edited by: drbsp on 2001-12-05 07:07 ]</font>

PETNRDX · Post by **PETNRDX** » Mon Dec 03, 2001 10:59 pm

You are probably on the edge of the VCO range. I would recommend that you check to be sure the VCO voltage is correct and also go in and set the TX power output down maybe 10 or 15 percent just to keep heat and current limiting down. I have had a couple of the Maxtrac/Gm300/Radius series radios go into the over current/high swr shut down mode when using them outside the design band.

Will · Post by **Will** » Tue Dec 04, 2001 2:08 pm

At 477 mhz, the radios microprocessor does not set up the D to A converter that sets the transmitter's power output and deviation. So the transmiter runs at FULL power, gets really HOT and the microprocessor senses the heat and shuts down the VCO & transmitter. Try to set the power control on ALL set points down about 10 to 20 percent and that MAY help.
If the transmitter power output can not be controlled at the 470+ frequencies you may need to add a resistor/pot in the D to A's output to the power control to back off the power. Also the deviation on the transmitter goes way high on the 470+ freqs due to the same problem of no set points for the microprocessor to look up when "out of range" at 470+ mhz. This can also happen on some VHF radios in the ham band. This is more of a problem with the Maxtrac/Radius M series radios.