8506r 8506

Date: 03 Sep 90 16:31

Message-ID: <22513
From: VE4KV
To: ALL
Subject: Mod for IC-24AT

Path:      VE3EUK!VE3INF!VE3FJB!VE3KYT!VE4KV









          OUT OF BAND MODIFICATION OF THE ICOM 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

     it.

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"  

             key.

          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

                              (VHF)

     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

                              (UHF)

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

communications.



Good luck with your unit.



"73"

Joe Taylor, W9JO