IC24AT additional features (miscellany)
                =======================================

(Part 4)

Modification for freq. coverage extension
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1)    Remove Diode D13
2)    Keyboard  [B,#,LIGHT] & Power-ON

Does work...   FOR RECEIVE-ONLY!

The process is relatively simple; considering that most of the entire radio
is surface-mount parts...  It turns out that Diode D13 is one of two "normal"
sized diodes on the LOGIC BOARD easily accessed and cut when the radio is
opened...

(Two "standard" diodes are found below the logic IC1 by about a 1/3inch,
with IC1 at the top, looking at the diodes D13 is the one on the left.)

Result:  Recieve results (rough-info for about 6 hours of use after mod)

VHF:  PLL locks about 75MHz - 280MHz
        (display will go 0MHz to 355MHz)

UHF:  PLL locks about 355MHz - 500MHz
      PLL locks about 795MHz - 975MHz
      (display will go 355MHz to 1310MHz)

Actual use/operation:
Aircraft: (108-136) seems to detect AM OK. Seems that high-end of band
          receives better.

2m HAM: As shipped.

VHF HighBand (150-176): Seems pretty hot. Unit is shipped rec'ing this stuff.

220MHz: VERY Dead receive at these freq. Hears only very local transmitters
        **ALSO above 200MHz step rate is no smaller than 12.5khz!
        SO NOT ALL channels can be tuned on freq.

70cm (420-450): Fine

UHF (450-476):  Hot reciever! Best ham mod'd receive better than IC32AT mod
                rec... 470+ MHz works well.

800MHz (convential/trunking): It hears the band - perhaps about the same as
                              most scanners. Not as hot as above bands, BUT
                              fairly useable!

870-890 (cellular): Yes, but channel step rate is 12.5kHz and cellular is on
                    30kHz, so can not be on exactly every channel.

900MHz: Did not check out much here, also a lot of cellular images present.

Bottom Line--- ICOM 24AT is a NEAT VHF/UHF/800mhz reciever and 2m/70cm
                HAM radio in ONE.

The modification (D13 cut) provides a manner to receive extended band
coverage, without worrying about accidental transmission in other services;

Cross-band receive
~~~~~~~~~~~~~~~~~~
Order the diodes from Icom, part number 912-06015.  They are about $2.50
each.  A lot for a diode but not for a mod. These are tiny tiny surface mount
dual diodes.  They have three legs each and I forgot to see if they were
common anode or cathode.  Be safe and order the right ones from Icom.

Open up the radio.  Clip out the glass diodes D13 and D14.  D13 should
already be out to enable the rx mod but D14 will enable cross band repeat.
Func-C,5,D will activate the cross band repeat between two simplex channels.

Install the two diodes at position D7 and D12.  The picture below may help
find them.

I used the hottest and tiniest tipped iron I could find, tweezers and
magnifying glass.  Be extremely careful adding these diodes as I have seen
how easy it is to lift an etch.

 __________________________________
|                                  |
|                                  |
|     +------+                     |
|     | CPU  |                     | D5,6 Enable USA operation
|     |      |                     | D12  Enable UHF TX expansion
|     +------+                     |  D7  Enable VHF TX expansion
|                                  | D13  Disable expanded RX
|               D5 V  V D6         | D14  Disable crossband Rpt
|               D7 X  " D8         |
|              D11 "  V D12        |
|                                  |
|                                  |
|                  |  |            |
|              D13 O  O D14        |
|                  |  |            |
|                                  |
|                                  |
|                                  |
|                                  |
|    Mic              . .          |
|     _             .     .        |
|    (_=           .  Bat  .       |
|                   .     .        |
|                     . .          |
|                                  |
|                                  |
|__________________________________|

Compiled from a miscellany of comments found on Compunet.

(Downloaded from GB7SYP)