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

Thu Aug 20 16:29:31 EDT 2009

Adam et al,
I guess you could use a second receiver with an IC-756PROIII as well using
the splitter et al?  

I've been thinking a bit differently about this dual receive situation
because of the performance issues that sometimes come up, but more
importantly because of the operational requirements that I have.  It might
be cool to set up my PRO3 and PRO2 in a SO2V/SO2R configuration using two
separate 6M antennas and just protect whichever transceiver is idle when I
transmit with the other one.  The same strategy could be done on 20M, 40M,
etc.  I am blessed with separately rotatable antennas on different towers
which allows me to look west and south or northeast toward Europe while also
looking west or south as needed.  

I am thinking about using some small BNC Dow-Key relays and small dummy
loads all triggered by reed relays from the rigs and the PTT lines, as I
only use the exciters here with no amps.
Thoughts?

Thanks & 73,
Gordon Beattie, W2TTT
201.314.6964

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Adam Farson
Sent: Thursday, August 20, 2009 6:25 PM
To: 'ICOM Reflector'
Subject: Re: [ICOM] 7600 and Dual Watch... "it's a mix"

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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