[ICOM] New IC-7700 announced at Dayton

[Adam Farson]

Hi Jim,

The receivers in the IC-7800 have completely separate RF signal paths. Each
receiver has a dedicated preselector.

I have several articles written by British radio engineers who used to
design shipboard HF receivers for the Royal Navy. RF preselectors were
standard in all those applications.

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 Jim M.
Sent: Thursday, May 17, 2007 23:02
To: ICOM Reflector
Subject: Re: [ICOM] New IC-7700 announced at Dayton

The 7800 has an automatic front end preselector in the receiver.   If it is 
a good preselector, it will drastically attenuate signals outside of the
frequency range you are tuned to... maaybe 50-100 khz I would guess.  This
reduces strong signal intermod.  But that would make dual receivers
difficult.  The earlier Icom rigs had front end tuned circuits, mostly for
the transmit chain I would guess, but they also make it hard to dual receive
on different bands - the front end tuners would kill receiver performance
outside of the band of operation.  To perform well, a second receiver would
need its own dedicated automatic preselector, and signal chain, which would
drive the cost up.

Speaking of receiver preselectors, it's funny how things come back around -
a decade ago all the "experts" thought wideband receivers were the way to
go, no preselectors.  Fifty years ago the Collins people proved that a good
front end preselector made for better receiver performance (i.e. the old
R-390s).  Now they're back in the "modern" radios.  Just goes to show
there's really nothing new under the sun.  Jim N4BE





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