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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