[ICOM] 7600 and Dual Watch... "it's a mix"

[Jan Robbins]

Hi Dick and Adam,
I haven't used a 7600, but have found Adam's reviews of 7800, 7700, and 
7600 most useful and informative (as usual).
On the other hand, I CAN attest that the 7700 receiver outperforms the 
7800 (I had them in parallel for about a month), and that TWO 7700's, 
the receiver of one coupled to the other, is the best receiving setup I 
have ever encountered (have been using two 7700s that
way for more than a year now, and as far as I'm concerned it is the 
"only" way to get dualwatch without compromise).

Hope all is well with you gentlemen.  Thanks, as always, for all your 
help and good advice!

73 Jan N0JR

Adam Farson wrote:
> Hi Dick,
> 
> Dual Watch exacts two penalties in terms of RF performance:
> 
> 1. When DW is activated, the noise-band (idle-channel noise) at the Sub
> frequency is added to that at the Main frequency. This raises the system
> noise floor by 3 dB.
> 
> 2. There is an RF make-up amplifier ahead of each first mixer, and an IF
> make-up amplifier at the IF output of each mixer. These amplifiers make up
> the insertion loss of the splitter and combiner, respectively. The presence
> of these amplifiers in the RF and 1st IF signal paths will degrade IMD-free
> dynamic range.
> 
> http://www.ab4oj.com/icom/dw.html 
> 
> There are other factors in the superior receiver performance of the 7700 vs.
> 7600. The 7700 first mixer is a passive DMOS switch vs. a more conventional
> quad-JFET mixer in the 7600. The 770 mixer will thus have superior
> strong-signal handling. In addition, the 7700 receiver has dedicated,
> relay-switched RF bandpass filters and a tracking preselector (Digi-Del),
> vs. diode-switched shared filters and no preselector in the 7600. (Relay
> switching eliminates another IMD contributor.)
> 
> It is not too difficult to multicouple a second receiver to the 7700.
> 
> http://www.ab4oj.com/icom/ic7700/2rx.html
> 
> 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 Dick Flanagan
> Sent: 20-Aug-09 11:05
> To: ICOM Reflector
> Subject: Re: [ICOM] 7600 and Dual Watch... "it's a mix"
> 
> Having Dual Watch compromises the performance of the receiver.  You can have
> good performance with Dual Watch or better performance without it.  The 7700
> chose to go the route of maximum performance.
> 
> I would be curious to know if without Dual Watch the 7600 receive
> performance could have equaled that of the 7700.  If it could, it might have
> impacted sales of the 7700.
> 
> Dick
> --
> Dick Flanagan K7VC
> dick at k7vc.com
> 
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