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

Fri Aug 21 02:48:18 EDT 2009

Gordon,
    A simpler solution  is to use one of the WX0B StackMatches that 
allows one to TX/RX on one, two or three antennas at once. For TX the 
SWR on no one antenna can exceed about 1.7:1. These cover from 160 thru 
6m. I live in CO and in a 6m contest it is often possible to have the 
band open in  two or three or even more directions at once. If you are 
running 1500w, you can CQ with 500w in three directions at once which is 
quite effective. It is also handy for HF contesting and even with QRP 
I'll split the power between multiple antennas. It is handy for S&P to 
listen in multiple directions and quite easy to switch all the juice to 
a single antenna to make the QSO. From TI5N I would CQ with 2.5w to 
Europe and 2.5 to the US and would run stations in both at the same 
time. Jay (WX0B) could not believe I was able to do it at that power level!
    Be carefull with the II and III as the front ends are very poorly 
protected from nearby RF or ESD sources. Been there done that 5 times 
with my III at about $250 per repair!
    Phil N0KE

J. Gordon Beattie, Jr., W2TTT wrote:
> 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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