[Amps] IM big amps

[craig]

Harris Gates have a 10 kw solid state HF amplifier with a claimed IM 3
figure off minus 30 db PEP. One thing I have notice is that Harris and many
other commercial RF manufacturers are starting to use the PEP reference. I
always assumed that the commercial standard was IM below one of two tones.
Thales still seem to use the one of two tones measurement standard in
preference to PEP.

In regards to IM and transceivers, its a never ending battle to find a
decent transceiver with consistent IM performance across all  power levels
and all bands. The current batch of top range radios seem to be getting
worst.

Scanning through the IM3 figures of all the radios shows the top radios in
IM3 performance are the  following

1. JST 245 this radio has spectacular suppression of 5th order products
2. FT1000D
3. TS950SDX
4.  IC765

What is bizarre is that some of the older solid state radio have better
figures  than some of the newer radios. A radio like the TS50 seems to have
a similar figure to the current 200 watt FT1000MK5. Price seems to have
little do to with IM performance. I think the best solution appears to be
high voltage MOSFETS.

The only current top range model radio with superior IM performance is the
FT1KMK5, using class A. Why they chose this route over something like the
FT1000D which had excellent general performance in the 200 watt range is a
mystery. The current batch of final failures may see Yaesu go back to a
standard high IM 200 watt final like the FT1000D.

I think the big worry as Tom alludes to is the poor performers like the
TS2000, IC746pro, FT920 and even the well regarded TS850 which has severe
IMD problems.  When you start to approach the -20db level that's cause for
concern.
The most concerning aspect of this  is that a radio like a TS850 which has
known poor IMD performance has found favour with 6khz wide Hi Fi Audio
folks. These wide signals combined poor IMD can even be heard badly here in
VK when the band is open. I was clobbered by a fellow running this
combination  from 8 KHZ away! His comments was that there was nothing wrong
he was experimenting and was legally entitled to occupy that bandwidth. I
don't know what the FCC rules are, but the whole subject of standards and
bandwidth seem very unclear. If that is the case I may pull out my old 10
tube sweep tube amp, just kidding!

Craig
VK3HE