[Icom] FW: A DSP IF filtering test any IC-756Pro/Pro2 owner can perform

[Julio]

Warren have you tried this out? I don't think I understand it.

Julio
----- Original Message -----
From: "Adam Farson" <farson@shaw.ca>
To: "Icom Reflector" <icom@mailman.qth.net>
Cc: "GEORGE T. BAKER" <w5yr@att.net>; <W8LX@arrl.net>
Sent: Sunday, May 05, 2002 1:13 AM
Subject: [Icom] FW: A DSP IF filtering test any IC-756Pro/Pro2 owner can
perform


> I am posting this test procedure to the reflector on behalf of, and by
kind
> permission of, Rob Peebles, W8LX. The test procedure can also be found on
my
> Icom page:
>
> http://www.qsl.net/ab4oj/icom/w8lx.html
>
> Best 73,
> Adam, VA7OJ/AB4OJ
> North Vancouver, BC, Canada
> http://www.qsl.net/ab4oj/
> Note new e-mail address:
> mailto:farson@shaw.ca
>
>
> Good evening gentlemen.
>
> "Perhaps these are not what you would call "narrow filters" but they are
> adequately narrow to ultimately prevent overload of the DSP A/D
> converter(s) and that is all that is required." (Excerpt from George,
W5YR's
> posting of 5/1/2002)
>
> Try this test to convince yourself the above is true.
>
> Take your PRO and set up in the CW mode with a bandwidth of 50 Hz (with
BPF
> illuminated).  Tune in WWV at a time when the signal is strong (currently
20
> over S9 @ 15 MHz).  When you are zero beat perfectly (i.e. sidetone pitch
> matches beat note from the WWV carrier) all you hear is the carrier (no
> modulation, voice etc.).  Now tune up 100 Hz (due to calibration errors it
> might be easier for you to just move up with the RIT instead of the main
VFO
> after you find the true zero beat) and listen to the BCD time code. Notice
> how well you can hear the bit pattern of the time code (and how you don't
> hear much of anything else).  Set the AGC to fast and watch the digital S
> meter paying particular attention at the top of the minute when there is
no
> 100 Hz tone transmitted.  Pretty impressive for being 100 Hz away from
that
> strong carrier!
>
> Now go up to 150 Hz above the WWV carrier....don't hear a thing.  See how
> low the noise floor is?
>
> At 200 Hz above the WWV carrier  we see the harmonic of the 100 Hz BCD.
>
> At 250 Hz above it is spooky how much of the signal you don't hear!
>
> Now, go up to 500 Hz (even minutes) or 600 Hz (odd minutes) and listen to
> the standard audio frequencies.  Pay attention to the ramp of the tone
> coming and going in conjunction with the ticks (during the period of the
> tick the 500 or 600 Hz tone is briefly muted).
>
> 1000 Hz is the fundamental frequency of the ticks.  At that offset you see
> the ticks very nicely but nothing else - well unless it is an even minute
> then you hear the harmonic of the 500 Hz tone being transmitted!
>
> When you tune through WWV in such a manner and see how you can pick apart
> and separate the various components of their transmission without overload
> from the main carrier you get a pretty good feel for what kind of
"close-in"
> ultimate selectivity and noise floor that can be achieved with DSP
> filtering.
>
> Hopefully you can make enough sense out of my ramblings to try this at
home
> (I'm tired and just about to go to bed).  I've just re-convinced myself I
> don't want to go back to life before DSP.
>
> 73,
>
> Rob Peebles, W8LX
> Dublin, Ohio
>
> Postscript:
> Tuning 10 MHz now I can barely hear WWVH in the background.  WWVH's top of
the
> minute tone
> is 1200 Hz, and yes I can isolate it in the passband too (it is so weak it
> doesn't move the s meter).  I hear it much better on 15 MHz (where WWVH is
> stronger), and on 20 MHz (where I can't hear WWVH) it's gone.
>
> ----
> Your Moderator: Dick Flanagan W6OLD, icom-owner@mailman.qth.net
> Icom FAQ: http://www.qsl.net/icom/
>