[ICOM] PW-1 Problems and a solution

[Adam Farson]

Hi Ken,

As discussed in my solid-state amplifier article:
<http://www.qsl.net/ab4oj/quadra/sshfamp.html#1.5> and in Sabin, "HF Radio
Systems & Circuits" Ch. 12, the load impedance presented to the PA must be
held as close to purely resistive as possible, for optimum linearity.

For this reason, and also to get some additional receiver preselection, I
always leave the ATU in my Yaesu Quadra amplifier engaged. The matched ATU
insertion loss is about 0.5 dB. The ATU matches down to 1.1:1 or better.

The same arguments apply on the rare occasions when I run barefoot. I leave
the Quadra ATU in-line with the 1kW PA stage bypassed.

I agree that cascading tuners is to be avoided at all costs, as it can lead
to serious damage. As a solid-state amp has a "flat" resistive input
circuit, the exciter's ATU is not required when driving such an amp.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Ken Kinyon
Sent: 25 March 2006 07:50
To: ICOM Reflector
Subject: RE: [ICOM] PW-1 Problems and a solution

Hi Tony and all,
There is another aspect of this that I have noticed recently in postings to
many lists.
Granted transistors seem to be more susceptible to damage from high SWR than
vacuum tubes.
However there seems to a tendency on the part of hams to use the built in
tuner all the time even when the feed line SWR is low.
I never use the  tuner in the 756ProII or pw-1 if the SWR is less than 2:1.
In my opinion the heat generated by the power wasted in the tuner circuits
is more damaging than slightly more than 1:1 SWR.  Perhaps I am a dinosaur
and I am prepared for the ensuing bombardment, but I believe more effort
should be made to keep the SWR at the end of the feed line at a reasonable
effort and that tuners should be used less.  And yes, I know that the tuner
will narrow the band width of the interference that the receiver is
subjected to, but I don't believe that most hams live in that sort of an RF
environment.
73,
Ken W7TS



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