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 8506r 8506
Date: 03 Sep 90 16:31
Message-ID: <22513@VE4KV>
Subject: Mod for IC-24AT


     The Icom IC-24AT is truly a remarkable unit.  Having it's
genesis in the IC-R1, Icom's extremely wide band Hand Held
Receiver, it is capable of receiving a wide range of frequencies,
as well as being able to transmit on short excursions, outside of
the amateur two meter and 440 MHZ. bands.

     The more current models can be modified to receive out of
band, by a simple software (not necessary to physically open the
transceiver) procedure as follows;
   o Turn the power switch off.  While simultaneously holding the
     "light" button, the "B" button, and the "#" button, turn the
     radio on. All elements of the display will light up. 
     Continue holding the buttons until the display goes out. It
     may be helpful to have a buddy give you an extra hand during
     this procedure....Your unit will now receive out of band.
The older models of this transceiver, require the removal of
diode D13, before performing the above procedure.  D13 is on the
main logic board and is a discreet diode near the center of 
the board.  It is the diode on the left of the two on the board
when the radio is open and held with the controls away from you. 

     The "stock" transceiver, was also not designed, to provide
full direct keyboard entry of the operating frequency.  This can
also be modified by one or both of the two procedures below;
   o To directly key in the 10Mhz. frequency, simultaneously hold
     the "light" button and the "2" button, while turning the
     radio on.
   o To directly key in the 100Mhz. frequency, simultaneously
     hold the "light" button and the "3" button, while turning
     the radio on.

     The modification of the unit to enable it to transmit out of
the amateur bands is a fairly simple procedure. It is however,
complicated by the fact that the construction technique used in
this transceiver is "Surface Mounted Technology."  If you have no
experience dealing with this technology, you may well be better
advised to defer this procedure to someone who has.  It is
extremely small and delicate, and is best done with specialized
equipment.  Also, because the unit may not be FCC type accepted
for all the frequencies on which it can then transmit, it may not
be legal for you to use it, despite the fact you may be licensed
to transmit on those frequencies.  This information is provided
only for those who are licensed for and want to use the unit on
MARS and CAP frequencies, where there are no type acceptance
restrictions.  The procedure is as follows;
   o Order a couple of DA204u diodes from Icom or your Icom
     dealer. These are a special three terminal device with two
     diode in one package.  They are very very small, about half
     the size of one of the key buttons on the touch tone pad.
   o Locate and remove the diode device in position D8
   o Locate the vacant position of diode D7 and attach one of the
     DA204u diodes at that location.
   o Locate the vacant position of diode D12 and attach the other
     DA204u diode at that position.
   o If diode D13 (procedure above) has not been removed, remove
The unit will now transmit out of the amateur bands. 

The IC-24AT can also function as a Mini Repeater transmitting on
the UHF band while simultaneously receiving on the VHF band, or
vice versa. This procedure requires both a small hardware as well
as a software modification, and is performed as follows;
   o Locate diode D14. It is located adjacent to the location for
     diode D13 (see above procedure). Clip or remove it.
   o To enable Mini Repeater operation 
          1. Push and hold the "Function" key and then the "C"   
          2. Push and hold the "Function" key and then the "5"   
             key and the "D" key.
   o To cancel the Mini Repeater operation, push and hold the
     "Function" key and then push the "D" key.

The above modifications provided the following capabilities with
my particular unit.
                       FREQUENCY COVERAGE
     RECEIVE                                 TRANSMIT
74.9 Mhz. - 127.9 Mhz.                         OFF
138.0 Mhz. - 168.0 MHz.                 138.0 Mhz. - 159.0 Mhz.
174.1 Mhz. - 189.69 Mhz.                       OFF
200.0 Mhz. - 287.22 Mhz.                       OFF
310.0 Mhz. - 349.0 Mhz.                        OFF
355.0 Mhz. - 409.98 Mhz.                       OFF
412.37 Mhz. - 498.0 Mhz.                 410.5 Mhz. - 470.0 Mhz.
792.85 Mhz. - 966.66 Mhz.                      OFF

Receive sensitivity throughout both of the Ham bands was better
than .5 of a microvolt. Sensitivity in the 200 Mhz. range was a
disappointing 1 millivolt and in the 800 Mhz. band a good .7 of a
microvolt. Remember, while the unit will receive on those
frequencies, it is illegal to monitor cellular telephone

Good luck with your unit.

Joe Taylor, W9JO



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