[Icom] CI-V Interface and 756 Transmit Audio

[Greg Yost]

Hey Greg,
I'll take a look on the 756 I got from you the next chance I get, and let 
you know what I find. regards Greg W8RCA


From: "Greg Ordy" <ordy@seed-solutions.com>
Reply-To: icom@qth.net
To: <icom@qth.net>
Subject: [Icom] CI-V Interface and 756 Transmit Audio
Date: Wed, 16 Jan 2002 11:01:08 -0500

From: "Greg Ordy" <ordy@seed-solutions.com>

     Here's a message with two unrelated topics.

     I have put up a web page with yet another home-brew
CI-V Interface. The link is:

http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/CIVInterface.htm



     The second topic is a little more interesting. It concerns
only the standard 756 radio. I try to follow this list, and I don't
remember seeing this mentioned before, so I'll spew it out.

     Apparently 756 radios above some serial number around
2000 have an internal switch that allows the selection of
either a 'narrower' or 'wider' transmit audio bandwidth. I sold
my 756, so I can't confirm this, but I got email from a friend
with a serial number in the 4,000 range, and his has the
switch, and it functions as described below.

     Here is a little section of some private email that describes
what's going on. I didn't write this, and I received it as
a forward of a forward of a forward....

----------------------------------

I was listening on 14178 Monday night when you came on with the
revelation about the "secret switch" on the bottom of the IC-756!  I had
my radio opened up within minutes and flipped the switch to W.  It sure
makes a big difference in widening out the transmit bandwidth, both
highs and lows!

.....

I checked the service manual and found that the switch is labeled S801
and it grounds pin 10 of IC817 in one position.  Unfortunately, there is
no mention of either that switch, or IC817, anywhere else in the manual
(other than the parts list).  I called Icom Tech Support and they didn't
have a clue about the switch either!  (Big surprise!)  The technician
said he would "check with Japan" and e-mail me any additional
information, but I am not holding my breath.

I found plenty of fidelity available by just feeding the front panel mic
jack and playing around with the bass and treble transmit tone
controls.  The rig also seems more sensitive to audio overdrive and
compression, so you have to be extra careful.
...................

"I have discovered that not all IC-756s have the N-W switch.  I told a
friend about it and he looked inside his s/n 014xx unit and there is NO
switch!  I also looked at a photo on W2ENY's filter web site and there
is NO switch on his radio, either!  My radio's s/n is over 03100 and it
has the switch.
----------------------------------

Greg Ordy, W8WWV



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