[INRAD] Icom band decoders

[c-hawley at uiuc.edu]

Is there a circuit diagram somewhere? I have built these for 
my own use over the years and just offhand I'd say that a 
tweaking of the voltage divider for the input to the 
decoding chip may fix the first problem to better center the 
voltage input from the Icom (without knowing how it is 
designed). And, a 1 K or so pullup resistor may fix the 
second problem (again without any knowlege of how it is 
designed).
Chuck KE9UW

---- Original message ----
>Date: Fri, 27 May 2005 17:09:25 -0500
>From: K4RO Kirk Pickering <k4ro at k4ro.net>  
>Subject: [INRAD] Icom band decoders  
>To: Inrad List <list at inrad.net>
>
>I've been trying to send this to George and Dave directly,
>but there seems to be some kind of problem with an anti-
>spam filter rejecting my domain.
>
>I am having two different problems with Top Ten band 
decoders.
>
>The first problem is that they will not consistently engage
>the 160m meter position when decoding an older Icom radio. 
I 
>have encountered this before with other Icom rigs, and it 
had 
>to do with the decoder's break point between 80 and 160 
being 
>too close to the cross-over point of the analog band 
voltage 
>coming from the rig.  At one time I added a small battery in
>series with the band-voltage line to the decoder to bump it 
>up by 0.5 volts. That was enough to ensure consistent 160m
>operation.  This was a crude kludge, but it worked.  Is 
there 
>a more elegant way to get TT band decoders working with the 
>IC-781 and IC-765 series radios?
>
>The second problem started happening a few months ago on one
>band decoder only. The symptom is that one band position 
(80m)
>does not go to full high (12V) when NOT selected.  Instead,
>7 to 8 volts is present when measured at its corresponding
>six-way relay box 80m terminal.  The terminal sinks to 
ground
>(~1V) properly when 80m is selected, but it does not go 
full 
>high (12V) when not selected.  The result is erratic 
behavior,
>with high SWR on all bands and antennas, perhaps from two 
>antennas being selected simultaneously.  When I swap out a
>different TT band decoder, the problem goes away.
>
>Any insight to either of these problems would be much 
appreciated.
>
>Thanks,
>
>-Kirk  K4RO
>
>
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