[ICOM] ICOM PROIII saga update

[VE6JY Don Moman]

I would suggest there must be something unusual about your radio.  Having
used 2 756Pro's for several years, and just now, a PROIII; all of these
radios perform as I believe they should, and rather well too, in my opinion.
I have tried to duplicate the situation that brings the spikes you're seeing
and nothing like that is visible or audible here.

73 Don
VE6JY

----- Original Message ----- 
From: "Steve N4LQ" <n4lq at iglou.com>
To: "ICOM Reflector" <icom at mailman.qth.net>; <tentec at contesting.com>
Sent: Wednesday, December 29, 2004 23:50
Subject: [ICOM] ICOM PROIII saga update


I promised to give an update on my experience with the PROIII so here goes:
(note: I am posting this on the TenTec reflector because the Omni VI+ is
compared)

Here's an update on my PRO III saga.
I sent the rig back to AES for evaluation. I included the Spectrogram
print showing the distortion products.

http://www.webham.com/Noise%20Pulses.jpg

 Miles, the chief technician called me today. He compared my rig to others
and said he was
unable to hear anything unusual. He also claims to have called ICOM and says
they had "never had a complaint". (Isn't that what they always say)?
Miles put in touch with Mike Hanson, store manager, who agreed to a
total refund. What a relief! So far, I'm impressed with AES and give them
high marks.

It is my conclusion that the PRO series suffers from distortion when
presented with signals having a very fast rise time. This includes most
cw, especially from hard keying transmitters and static burst. These
distortion products exit the
speaker as short duration clicks from QRN and sharp, leading edge thumps
on cw. This is largely irrespective of signal strength and is actually
emphasized to some degree when activating the NR function.

Adding attenuation, reducing RF gain and turning off Pre-amps has no effect.
This is most obvious to the ear when using narrow
 bandwidths such as 250hz or less. The distortion products fall far outside
the bandpass, up to 3 khz!

Having used a PRO II for 2 years, I believed ICOM's claims of lower
distortion in the PRO III. Maybe there is less distortion by some
measurement or some condition but certainly not CW and I believe the PROIII
is somewhat worse than the PROII in this regard.

BTW: I do love the bandscope and especially the newer version. Also,
although annoying and tiring to listen to, the PROIII is still able to pick
weak signals out of QRN better
than a few other rigs I have tried.

To answer a few FAQs:

The two rigs were connected via shielded cable from their low level audio
outputs to the sound card input. The gain of each input was adjusted for
near equal amplitude. The lower waveforms are the important ones. You are
not seeing amplitude spikes here. You are seeing noise pulses of various
frequencies. The center frequency was 600hz. This would be in the center of
the dark blue area. Note the spikes kicking up to 3 khz. These are head in
the headphones or speaker as clicks. There is no cw signal other than static
here. A cw signal would produce a solid yellow line through the blue area.
Nothing should be seen beyond the 250hz bandpass.
No. I wasn't overdriving the sound card.

Steve N4LQ
----
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