[Elecraft] IMD and supply voltage

[Joe Subich, W4TV]

CW is just one mode and is the easiest to "get right" as far as the PA
is concerned.  CW bandwidth is determined primarily by keying shape and
phase noise in the synthesizer (or D to A clock jitter).

The K3/K3S is far from the cleanest rig when it comes to SSB on any of
the audio based digital modes.  All of the rigs using 48V finals have
IMD products many dB less than the K3/K3S - particularly when the
K3/K3S is being run from a partially discharged battery.

However, even rigs with 48V finals are notably more dirty than many of
the rigs that used tube type finals (particularly the 6146) of 40 years
ago.

Amateur rigs need predistortion - particularly those with "12V" finals -
to get SSB (and data mode) IMD below -50 dBc (-44 dB PEP) as a starting
point or "12V" radios should be limited by their makers to 60-80W where
the IMD is much lower than at 100-120W levels.

For ARRL to have silently watched transmit IMD degrade by nearly 20 dB
in the last 40 years and not raised the issue is unconscionable.

Lest anyone think I'm picking on Elecraft ... the IMD issues are the
same in many solid state amplifiers, they are rated for saturated
conditions which drive up IMD.  Most are significantly less dirty when
operated at 60-75% of rated PEP output unless the designer has built in
a significant amount of negative feedback.  When a 1200W PEP amplifier
has only 8 150W transistors or or a 600 W amplifier has only two 300 W
transistors that's a good sign the amplifier can not possibly be clean
at its rated output.

73,

    ... Joe, W4TV

> On Thu, Oct 29, 2015 at 2:58 PM, Jim Brown <jim at audiosystemsgroup.com>
> wrote:
>
>> According to ARRL measurements, the K3 produces the cleanest CW signal of
>> any current rig. See my summary of their published data in the following
>> link
>>
>> k9yc.com/TXNoise.pdf
>>
>> See my measurements of my K3 and several other rigs in this link
>>
>> http://k9yc.com/P3_Spectrum_Measurements.pdf
>>
>> 73, Jim K9YC
>>