Batboard

Is anyone aware of a mike gain control on the GM300 line? I know there are hardpots for other functions.
tnx
Andy

If your refering to the 438 to 470 uhf rf bd then yes theres three blue pots on the bd.
Closest blue pot to the front is reference oscilator deviation adjustment.
next one going towards rear is the sqeulch setting pot and youll see SQprinted on the bd next to it.
Going further rear ward is a third blue pot near center of bd known as R302 mike gain and this one sets the mikes audio gain by turning clockwise or counter clockwise for the desired mike audio gain output.( its located just above the 14 pin brown strip pin conector middle center of rf bd.
Usualy there marked from factory with a marker when set to proper factory specs so you should be able to see if its still where it belongs or was moved.
Could be dirty just needs a cleaning and reset ????
Satelite

Actually this is a VHF unit. I don't really want to adjust deviation. Already did that through RSS.

There is no mic gain on a GM or Maxtrac.
The R302 POT is the VCO modulation and it affects both mic and PL deviation.
The only real way to up the mic "sensitivity" is by going thru the alignment and setting things higher.
That said, you *MIGHT* be able to turn up the dev with the VCO mod pot and *MAYBE* set the PL down a little with the REFERENCE pot.
You have found one of the weaknesses of that particular line.

Thanks for the responses. I had looked around online and did some searching, hoping to find a hardpot control. This involves a project I am working on.
I have a weather station at the house. The device I have takes the serial data from the console and converts it into spoke weather parameters, (temp, rainfall, wind, etc). The deviation was peaking about 2.5 khz with the device. With a microphone its right at 5.0khz. Both measurements taken on my service monitor.

Is it going to need to send PL?
If not, then you could crank the DEV settings in RSS or the pot up to where it gets to where you need it.
The PL DEV would be way wrong unless you did a pretty much full alignment.
Then again, if you are sending data, you probably want around 3.2 khz dev.
Might not be to hard to get that.

The mike input impedance is around 600 ohms. Your weather station might be expecting a higher impedance load, and it just doesn't have enough drive to make the GM300 work. See if you can add a small buffer amplifier between the two. You'll need around 80mV per kHz of deviation when plugged into the radio. Even something as simple as an emitter follower might be good enough if there's already enough audio coming out of the weather station.

Otherwise there is no mike gain control or jumper in those radios.

Bob M.

I am not using PL. No need to since the "reporting" function is transmit only. I can set the unit to report on demand but for now it is on a stand alone txmtr beaconing every hour. I am not going to leave it on beacon mode permanently, just during this testing phase. With the lower deviation, it really doesn't sound to bad and reports from other operators plus my own observations out in the field indicate it is perfectly usable, even at the lower audio level.

One thing I have considered, is bringing the audio in from the 16 pin accessory port. See if that makes a difference.

Andy

Look for JU651 on the logic board, position A is low gain (80mV rms for 60% deviation), position B is high gain (40mV rms for 60% deviation).

Also note that the mic input has voltage on it. It's meant to be driven by an open collector amplifier in the mic.