Subject: IC-901A Frequency Ranges

From: Chuck Adams <[email-masked]>
Date: Tue, 6 Oct 1992 13:59:35 GMT

In article <[email-masked]> [email-masked] (paul) writes:

>Does anyone know the extended range of the various IC-901A modules?  I'm
>particularly interested in the 10m and 6m modules...  and how they relate
>to the VHF-Lo band.
>
>Any other undocumented tricks with the '901?

Here are the frequency coverage ranges for the various band modules and the
modifications to the control head diodes to get these extended ranges:

Band     Range (MHz)      RX diode       TX diode

10m       28-40            24 out         21 in
6m        40-54            28 out         26 in
2m        138-174          no change      18 in
220       216-236          no change      12 in
440       400-479          25 out         23 in
1200     1240-1300         no change      no change

To modify, remove the back of the control head and add or remove diodes from
the marked pads as described in the above table.

notes:  coverages are for RX.  TX may not work over entire range, but will come
close.  RX sensitivity is front-end tuning dependant.  10m, 6m, 2m and 1200
modules will have OK RX sensitivity over most of their range.  220 RX sensivity
is unknown over its' range.  440 RX sensitivity will cover about 25 MHz with
good sensitivity, tuning out of the box is from about 438-463.  The 3 helicals
can be retuned to any where in the 400-479 MHz range, but you can still only
get the 25 MHz or so spread.  If you have severe intermod problems while
listening to 440 MHz frequencies, I would recommend retuning the helicals down
in frequency to attenuate the strong 450-460 MHz signals from the front end. 
The intermod will almost completely go away.  Of course, the sensitivity above
450 MHz will suffer, but most of the signals you would probably be interested
in listening to will probably be quite strong to start with, so you will
probably still hear them just fine.  If you have access to a tracking generator
and spectrum analyser, there is a small two pin jack on the UHF board from
which you can monitor the helical response.  Connect the tracking generator to
the antenna jack and the spectrum analyser to the two pin jack.

Other '901A tricks:

Memory and microprocessor reset - turn power on while holding down check and
memory write buttons.

Crossband repeat - turn power on while holding down check and lock buttons.  If
crossband repeat has been engaged, the "lock" display will flash.  PL can not
be selected in either band for crossband repeat to work. If you need PL to
operate the repeater you are linked to, generate it on the radio you are using
to talk to the 901.  The PL will pass through the 901 just fine to access the
linked system.  Since the radio is in the locked mode, you can't change
frequencies or bands during crossband repeat.  To disengage crossband repeat,
turn off power or press lock button.  If there is no audio during crossband
repeat, open up the front of the dual-band unit by removing the plastic cover
behind where the control head would plug in if the 901 is not used in the
remote-control head configuration and look for a slide switch mounted on the
edge of one of the vertical circuit boards and slide it the other way.  The
switch does not seem to come in any pre-determined configuration from ICOM, so
some radios work OK for crossband repeat right out of the box, and some require
the switch to be in the opposite position.

I would be very interested in any other mods or tricks for the 901.

                      Chuck Adams,  WB5WRR   (The Chuckster)
                 Not an official document of DOE, SSCL, URA or EG&G
             "I cut you three ways, man:  quick, deep and frequently"
                       Internet:  [email-masked]