[Elecraft] IMD of MOSFETs vs. bipolar

[Wayne Burdick]

Like everyone else, we switched to 12 V VHF MOSFETs for our 10 and 100 watt PAs. At the recommended supply voltage (~14 V), IMD for these transistors is about the same as for bipolars, with 3rd order products averaging -35 to -40 dBc and worst-case about -30 dB. These stats are borne out by an average of QST review numbers going back over the last 30 years.

It is true that at lower supply voltages, bipolars "gracefully degrade" with more grace than MOSFETs. So if IMD is of primary concern when using lower voltages, you may choose to reduce power somewhat. (Of course this is a useful practice when running from batteries.)

Reducing power while maintaining communications effectiveness recently became a whole lot easier on the K4 with the addition of CESSB. In our tests, average power went up by over 6 dB between settings of CMP=0 and CMP=30.

73,
Wayne
N6KR



> On Jun 28, 2022, at 7:08 PM, jerry <jerry at tr2.com> wrote:
> 
> On 2022-06-27 15:23, Dynolab wrote:
> 
>> Since the semi manufactures stopped making Bipolar RF Power transistors in
>> the middle of the last decade, most Ham HF transceiver manufactures were
>> forced into using ... 12 Volt MOSFETs in their finals.