[ICOM] Icom Dual Watch

[John Germanos]

Adam,

Your Block diagram of 756ProXXX explains what I was missing! 

73 John

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Adam Farson
Sent: Saturday, November 29, 2008 12:53 PM
To: 'ICOM Reflector'
Subject: RE: [ICOM] Icom Dual Watch

Hi John,

Here is an explanation of Dual Watch.

http://www.ab4oj.com/icom/dw.html

With the Pro3's DW architecture  (splitter, A & B 1st mixers, combiner,
roofing filter) then both A and B signals will be up-converted to the same
1st IF frequency. This frequency will ultimately pass through the IF-DSP
selectivity, and will thus be well within the passband of the roofing
filter. 

In any event, if both A and B channels appear in the baseband output with
correct pitch, they will have passed through the roofing filter and the DSP
IF filter (with minimum attenuation in both filters.)

If the A and B signals are in different bands, the RF bandpass filter
(selected by the A VFO setting) will attenuate the signal on B.

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 John Germanos
Sent: 29-Nov-08 04:45
To: 'ICOM Reflector'
Subject: [ICOM] Icom Dual Watch


Lots of discussion about this topic.
I might be wrong, but how would Dual Watch be very effective when using
narrow roofing filters.
The 756PRO has a fixed 15KHz roofing filter, so I can see that Dual Watch
would allow me to listen "up five to ten", while chasing after a SSB DX
station, for instance.
However, if I have a newer radio 7700 or even the 7600) with a 3KHz roofing
filter selected, I don't see how I would be able to listen "up five to ten",
with the Dual Watch system, very effectively.
Roofing filters are designed to attenuate signals slightly above and below
the wanted listening frequency.

Narrow roofing filters (with all their benefits) or Dual Watch. Don't see
how you can "have your cake and eat it".
Narrow roofing filters are great for contests. Dual Watch is great for
chasing DX.

What am I missing here?

John WB9PNU

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