Dave, Paul made some excellent responses to your questions. I'd like to provide additional information regarding your question #2.
<snip> > 2. Why is a 50w 2m transceiver, derated to 25w and driving a power amp > a bad choice? Or is it OK? <snip> My radio club once had a packet station, operating as a node, that used an FT-2500M 2m radio. Since the site was at an elevated location and we had a DB-224 antenna made for the 138-150 MHz split, we ran the radio at its lowest power setting- which I believe was around 8 watts. I was very surprised when the radio died after more than a year of faithful service. Like many imported 2m mobile rigs, this radio used a typical 50 watt RF module as the power amplifier. After replacing the module, which cost about $85, I ran some bench tests using a calibrated service monitor and a metered power supply. I quickly found out why the radio burned up when set for low power: The DC current draw decreased only slightly when the RF power was greatly reduced! In fact, the DC input power at 8 watts RF output was about 85% of the input power at 50 watts output. The extra power that wasn't generating RF was expended in heating up the driver and the output module. I suspect that the class of operation was tending toward AB or B as the drive level was reduced. Regardless of the mechanism at work here, I proved that the radio ran hotter at reduced power levels than at 50 watts output. Most commercial radios can run at 50% power levels and still be quite efficient. However, many of the Amateur-grade mobile radios I have tested- by no means an exhaustive sampling- run quite hot at reduced power levels. YMMV... 73, Eric Lemmon WB6FLY
