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[CQ-Contest] Thoughts on the 756PRO for contests

Subject: [CQ-Contest] Thoughts on the 756PRO for contests
From: jjarvis@keithley.com (jljarvis)
Date: Sat Mar 10 11:20:31 2001

I've had a PRO for a year now.  Dumped my 781 when I got it.  It remains a
good decision.

The DSP filters are just fine.  There is only one flaw in the rig...and it
may or may
not affect your perception of contestability:

There is a low-frequency, low-level signal which shows up in the audio,
which I suspect
is a derivative of the 2 stage AGC control signal.  This can be annoying in
heavy pileup
situations, as it adds to background noise.  This caused some of the
criticism of the radio by
early adopters in FRC.

The reason I suspect AGC, is this signal is level dependent, but not
determined by total
integrated signal within the upper IF passband.  i.e. ONE strong signal will
generate it.
(and it SOUNDS like that signal, if you listen closely.)  On SSB, it has a
syllabic voice
content, like listening to SSB with an AM diode detector.  On CW, it can be
mistaken for "clicks".

It only happens when the strong signal is within the 15KHz wide upper IF
"pipe".  Outside that,
I have yet to hear intermod.  One cannot disable the AGC in this radio, as
you can in the 781.
You can only change the AGC time-constants.  There is no noticeable change
in the artifact when
tc's are changed.

You have to wear phones to hear this...and it's best noticed when you turn
the audio one step above off.
As you go above that level, regular receiver audio swamps it out, except
when super-strong signals
are in the passband.

Caveat:  The published reports from DLARC and RSGB, reflect degraded
skirts....but don't
recognize the source of that degradation as I describe it.  Perhaps too
narrow a reliance
on test methods, and too little listening.  Or perhaps my radio is unique?
One could argue that it
doesn't matter... I believe it does...and that the problem can be cured.

My major complaint:  Icom steadfastly refuses to acknowledge this, or to
engage in meaningful
discussion with their client about it.  In my 30 year career, I've written
enough instrumentation papers,
and proofed out enough broadcast stations that I'm quite certain about what
I'm hearing.  What I'm
not certain of is the source of the offending signal.

If I am correctly identifying it as an AGC leakage of some sort, there may
be a decoupling solution
which would make a serious improvement in the radio.  But we won't get there
if Icom isn't willing to
listen and learn.

My belief is that as it stands, the radio is better than an MP, but not as
good as a 1000D.


-----Original Message-----
From: owner-cq-contest@contesting.com
[mailto:owner-cq-contest@contesting.com]On Behalf Of Lee Buller
Sent: Friday, March 09, 2001 6:14 PM
To: CQ-Contest@contesting.com
Subject: [CQ-Contest] Thoughts on the 756PRO for contests

My local contest buddies and I are in a debate on the "contestability" of
the IC756PRO.  I wonder if anyone out there is using the IC756PRO on both
CW and SSB contests.  I've read the reviews at www.eham.com, but I still am
not convinced about how the PRO works on CW and SSB with the DSP filter
scheme.  What do contest users have to say?

You may want to respond to me directly because this might have already been
discussed on the reflector.  I could not find anything in the archives per
se' this topic.

Lee - K0WA

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