Motorola GM300

These radios work great with the XIPAR Radio Over IP package and a USB Radio Interface. For Amateur Radio applications the radios must be the version that covers the Amateur Radio band and be programmed to specific channels.

They can be remote controlled by the XIPAR software to select pre-programmed channels if the accessory connector is properly configured with software.

Also because they feature Flat Tx and Rx signal points they can be used with the XIPAR CTCSS encode/decode capabilities for coded dialing and multiple sub-audible tones.

Finally using that feature, a pair of these radios (with a fan blowing across the transmitting radio's heatsink!) can be connected to form a reasonable repeater.

Xelatec provides ready to go USB Radio Interfaces with either single or double pre-wired radio connectors here.

For example, here's how I set up a pair of GM300's as a XIPAR controlled repeater for Buddy Brannan, KB5ELV.

First, I programmed the radios to the proper operating frequencies.

Second, I opened the radios and set the transmitter limiter (and adjusted the modulation balance control) for +/- 6 KHz peak deviation. This must be done to allow the XIPAR controller to provide the desired +/- 5 KHz deviation limiting. Otherwise the interaction between the two limiters will distort both the voice and sub-audible tones. Radios listening to the repeater with tone squelch may experience drop outs and regenerated DTMF tones might not be decodeable.

Third, in order to allow the XIPAR controller to provide good carrier detect and RSSI signals, a resistor must be added to reduce the gain of the Rx Audio amplifier so that it does not limit with no RF signal applied. To do this there are holes on the board to add a 100K Ohm, 1/8 Watt resistor in parallel with R579.

Then after following the standard installation instructions it worked fine.

Refer to this page at the Repeater-Builder site for a schematic, parts layout and additional information.

73, Steve Henke, W9SH