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Telamon · January 4th 09, 03:30 AM posted to rec.radio.shortwave

In article
,
wrote:

On Jan 4, 12:38*am, Billy Burpelson wrote:
wrote:
* ...just got up from my afternoon nap - too much lovely local wine at
lunch......
Icom has released very few details but what
is known is that it still has the "dual watch" feature that the hams
insist on, but Adam explains to me that this means they attenuate the
MW and LF bands same as the 756pro3 = pity!!

Mr. Plimmer,

Either I misunderstood what you wrote, you mis-spoke or you are still
enjoying the after effects of that "lovely local wine at lunch...". * ;-)

Indeed, hams do like the dual watch feature, primarily for "split"
operation when chasing DX.

However, I am puzzled as to why that feature (dual watch) would require
attenuation of the MW and LF bands. I thought this was done to reduce
intermod because of the very powerful signals in the MW band (nothing to
do with dual watch). Attenuation of MW is commonly done even in
receivers -without- dual watch. Could you please elaborate on this
presumed connection between these two features.

Hi Billy,
No my poor old brain was not too befuddled with the wine. I tried
to find in my old mail Adam Farson's description to me of why dual
watch exposes the radio to more intermod than on the 7700, but alas I
can't find it.

Adam is a very highly qualified radio engineer and I am sure he will
explain it to you in detail why dual watch requires attenuation on LF/
MW. You can contact him at:
farson_at_shaw_dot_ca

The IC-7700 does not have dual watch, and with it's better circuitry
does not attenuate on MW/LF where it is supremely sensitive and quiet.

I would speculate that the continuous switching between two channels
requires low pass filtering be eliminated for that function to operate
leaving the receiver open to saturation or intermodulation by MW signals.

--
Telamon
Ventura, California

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