[Icom] PW1 ?

Fri, 27 Jun 2003 22:51:42 -0700

Hi Bruce,

The Acom IMD3 figures I posted came from the ARRL Product Review (QST, May
2000) and Expanded Test Report on the Acom 2000A.

Generally speaking, if a Class AB or Class B linear power amplifier is run
at a small fraction of its output, crossover distortion becomes more
significant; this will tend to degrade overall linearity. However, in your
station setup, where 12W drive produces 1.5kW output, the IMD3 and IMD5
contribution of the exciter will be negligible. If you extrapolate the
example I gave in a previous e-mail, you will see this.

In practice, with voice SSB, the IMD products generated by the amplifier and
exciter will be all over the map phase-wise, and will seldom add. I would
not be too concerned - but you might be a little better off running 1.5kW
with about 50W drive. Also, at the 500W output level, your Acom will
probably have slightly lower IMD3 than at 1.5kW. This will tend to offset
the increase in IMD3 from the IC-781 at low drive levels.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Bruce Marton
Sent: Friday, June 27, 2003 05:51
To: [email protected]
Subject: RE: [Icom] PW1 ?

Adam,
What I was interested in was the effects of running the 781 at the 12
watt level.  Is there an inverse relationship of output to distortion
with respect to output level set.
I have been told that the "best" distortion numbers on solid state
devices are usually found a full rated output, not above and not below.
Most people think that running with the power scaled back will improve
distortion numbers with solid state rigs, but this may not be so.  Do
you have any info to support one way or the other on this subject???
I like running my unit at minimum output to drive my 15 db gain Acom to
around 500 watts out.  It makes a super nice 500 watt transceiver.  With
just a little more output (still not pushing the 781 or Acom at all) I
can run a 1KW transceiver and everything is still loafing along at an
idle.
If I recall correctly, the distortion numbers for the Acom were well
into the mid 40's down, but you may want to check that for sure.
Bruce K1XR