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1994-06-04
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Date: 17 May 90 15:54:21 GMT
From: hpcc01!col!kenw@hplabs.hp.com (Ken Wyatt)
Subject: IC-24AT Receive Mods
At the request of several interested hams, I am posting the modification
instructions for the Icom IC-24AT. This set of instructions originated
from Icom America and was downloaded from the Icom Library of HamNet
(Compuserve).
IC-24AT Undocumented Features - (from ICOM)
The IC-24AT dual band handheld had three additional features that
are not described in the owners manual. These have been left out
of the owners manual because some countries restrict the use of
the radio in these modes.
AM AIRCRAFT RECEIVE PLUS 740 to 960 MHz RECEIVE
Remove D13 from the main logic board (this diode may already be
removed by ICOM in some units). This diode may already be
removed in some radios. D13 is on the main logic board and is a
discreet diode (one of the two in the radio) near the center of
the board. It is the left discreet diode of the two on the board
when the radio is open and held with the controls away from you.
Simultaneously hold "Light", "B", and "#" keys depressed and turn
power on.
It is important to note that the radio will not meet specifica-
tion on the out of band receive frequencies that are enabled with
this modification.
DIRECT KEYBOARD ENTRY of 100 MHz FREQUENCY
Simultaneously hold "Light" and "3" keys depressed and turn power
on.
CROSS BAND REPEAT (simplex)
Remove D14 from the main logic board (this diode may already be
removed by ICOM in some units). The diode is a discreet diode to
the right of D13 (from above) and directly beside it.
Simultaneously hold "Funct" depressed and push "C".
To turn on cross band repeat:
Hold "Funct" depressed then push "5" and then push "D".
To turn off cross band repeat simultaneously hold "Funct" and "D"
depressed.
==============================================================================
There is a later version of IC24AT that does not require
D13 as in a previous bulletin.
All programming of extended frequency coverage is available
from the keyboard.
To Enable extended freq coverage - 75 to 195, 200 to over 900 Mhz.
Hold down Light, and B and turn on, wait for display to stop.
To enable 10 and 100 Mhz digit entry direct from keyboard:
Hold down light and 2 key and turn on, then turn off.
Hold down light and 3 key and turn on.
==============================================================================
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.
==============================================================================
The receive frequency range of the ICOM 24-AT will be 108-174, 400-480
and 750-940 Mhz.
To direct in the frequency:
1) Hold the "LIGHT", "B" and "#" keys (3 keys) and turn the power on. Release
the keys after the display fills up and shows a VFO frequency.
2) Hold the "LIGHT", and the "2" keys and power up. This make the 10mhz
direct entry possible.
3) Hold the "LIGHT" and "3" keys and power up. This makes the 100mhz direct
entry possible.
==============================================================================
Following the frequency expansion modification (as specified by Icom), a
sample IC-24 was recently tested for tuning range and input sensitivity
for an S9 signal. While the sensitivity measurements should not be directly
compared with the manufacturer's specifications (usually measured reference
to a signal-to-noise quieting ratio), this "quick and dirty" data should
give you a good idea of the sensitivity to a medium-strength signal.
Tuning Range Mode Band Sensitivity for S9 Signal
74 - 107.995 MHz (fm) VHF range approx 1 mV
108 - 136 MHz (am) VHF range 10 - 30 uV
138 - 240 MHz (fm) VHF range 1 uV - 1 mV (1)
250 - 302 MHz (am) VHF range 50 uV - 1 mV (2)
310 - 354.995 MHz (fm) VHF range 50 uV - 3 uV (2)
355 - 409 MHz (fm) UHF range 3 - 10 uV
417 - 490 MHz (fm) UHF range 1 uV - 100 uV (3)
805 - 955 MHz (fm) UHF range 10 - 100 uV
Notes:
(1) The sensitivity from 138 - 150 MHz was 1 uV. From 150 - 240,
the sensitivity decreased almost linearly from 1 uV to 1 mV
(with input voltage plotted logarithmically).
(2) The sensitivity increased almost linearly for both these ranges
(with input voltage plotted logarithmically).
(3) The sensitivity plot looked like a "U" with the bottom of the
"U" corresponding to the range 440 - 450 MHz (1 uV). The
sensitivity then got worse below 440 and above 450.
==============================================================================
The Problem:
------------
The Icom IC-24AT (and IC-2SAT) Second Keyboard Functions are activated by
pressing AND HOLDING the "FUNCTION" button on the side of the transceiver
WHILE pressing the keypad with the desired 2nd function. The disadvantage of
this procedure is that it requires 2 hands to activate a 2nd key function,
1 to press AND HOLD the FUNCTION button and 1 to press the keypad with the
desired 2nd key function.
The Solution:
-------------
I modified the operation of the FUNCTION button so that it only has to be
pressed MOMENTERLY to activate the function mode, it remains in the function
mode for approximately 4 seconds thereafter. Any second key functions may be
selected any time during the 4 second interval the function mode remains
active. The beauty of this feature is that now you can squeeze the FUNCTION
button with your thumb and then have up to 4 seconds to select the desired
2nd key function with the index finger of the same hand!
The Mod:
--------
Implementing this modification requires one 4.7uF 10 volt chip capacitor
and one 1K Ohm chip resistor. The negative terminal of the chip capacitor
is soldered to ground. The 1K Ohm resistor is soldered directly to the
positive terminal of the chip capacitor. The other terminal of the chip
resistor is soldered to the FUNCTION key PC board contact via a small
length of fine wire. THATS IT! It works great! I had mine in operation for
over 1 year. I could NEVER go back to the original procedure!
==============================================================================
The 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 turms out that Diode D13
is one of two "normal" sized diodes on the LOGIC BOARD easily
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 begins to lock in at about 75mhz ...
and goes out of lock at about 280mhz
(display will go 0mkhz to 355mkhz)
UHF: PLL begins to lock in at about 355mhz
and goes out of lock at about 500 mhz...
PLL begins to lock in at about 795mhz
and goes out of lock at about 975 mhz...
(display will go 355mhz to 1310mhz)
Actual use/operation:
Aircraft: (108-136) seems to detect AM ok...
within 2 miles of Ohare Intl(ORD)
recieve of ground 121.--- moderate
receive of ATIS 134.--- good
recieve of tower and approach moderate
seems that high-end of band receives
better.
"looks like for a pilot who desires
to monitor ops at the port
prior to run-up or whatever
should work fine)
2m HAM: As shipped.
VHF HighBand (150-176): seems pretty hot-
unit is shipped rec'ing this stuff
220 mhz: 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- (UUCH!)
70cm (420-450): Fine
UHF (450-476): Hot reciever! - best ham mod'd receive
- better than IC32AT mod rec...
470+ mhz works well-
chicago has allocations
of Public service and
business in 470-476
...and 24at works well
800mhz (convential/trunking):
Ah..it hears the band- perhaps
about the same as most
scanners- Not as hot as above
bands- BUT actual 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...
did hear a few chicago
trunking systems at the
935 trunking band---
935 trunking band---
*also a lot of cellular images
present.
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;
[however I would like to see 420-440 xmit at least
as I have repeater link/control in that
part of the HAM BAND; also 220 mhz freq&xmit
would be real neat; as well as 900mhz xmit
which a few repeaters do exist in the
area]
will do???))))
==============================================================================
I received the following mods for 24AT out-of-band from a very reliable
source (although they don't specify RX only or RX/TX), for 75-195 MHz,
200-490 MHz, and 740-960 MHz. Rumor has it (unconfirmed) that the unit
even switches to AM in the air band!
1. Remove diode D8 [see figure below]
2. Attach diode D7 [I believe this is already equipped]
3. Attach diode D12
4. Remove diode D13
5. Simultaneously hold "LIGHT", "B", and "#" keys and turn the
power on. Release all keys after the display goes out (checks
all LCD segments). [This is supposed to enable the
out-of-band frequencies above]
6. Simultaneously hold "LIGHT" and "2" keys and turn the
power on. This enables the 10 MHz frequency digit entry.
7. Simultaneously hold "LIGHT" and "3" keys and turn the
-- power on. This enables the 100 MHz frequency digit entry.
__________________
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| CPU |
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|________________|
o o o D7 lower left pin is
[D7] [D8] anode of one diode,
o o o lower right is cathode
of the other. Top pin
o o is common
[D12]
o D12 upper pins are cath-
odes of diodes, lower
is common anode.
__I_ __I_ See text
| | | |
D13 |__| | | D?
|/\| | |
| | | |
|__| |__|
I I
WARNING: I have NOT tried the hardware mods and cannot vouch for them, so
proceed at your own risk!
I am told that the newer 24AT's (believed not to have made it to the US
yet) will have the hardware mods in place, so only steps 5-7 will be
necessary. So, try this first. Steps 5-7 don't seem to have any effect
on a 24AT without the correct hardware mods. BTW, this has been attempted
on 2 units with serial numbers around 1000 and mid-1100's, neither of which
worked. :-( Like I said, the ones with the mods aren't here yet.
There are 5 screws to remove the case (5th is on the strap hook). Keep
the top panel controls with the front of the radio, and be VERY careful
pulling the back off because there are fine ribbon cables connecting the
front & back. I don't think they'll take much flexing.
Additionally, diodes D7, D8, and D12 are surface mount components. They
contain 2 diodes connected to 3 pins. Diodes D7 and D12 are different
configurations. I believe D8 and D12 are different, so I wouldn't put the
removed D8 in the spot for D12. Since they are surface mount, removal of
D8 may not be all that difficult for those with steady hands and a fine
low power soldering iron, but adding D12 would be a bear. I know of no
reason that small discrete diodes couldn't be used in for D12. D13 is a
small but standard axial diode, and can be easily cut.
==============================================================================
Usable ranges after the mods will be:
RX: 114-130, 138-192, 403-485 & 825-903
TX: 138-168, & 410-485
In reality I have seen a great variance between different radios on
where they actually lock up but I have been impressed at the
capabilities of this radio
I assume you already have done the kbd mod for the out of band recieve
so I will skip that part.
Order the diodes from Icom, part number 912-06015. They are about
$2.50 each. A lot for a diode but not a lot to spend for the mod.
These are tiny tiny *tiny* surface mount dual diodes. They have three
legs each and I forgot to see if they were common anode or cathode or
back to front. 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 surface mount 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. The extra temperature helps in soldering but you
have to be quick. Be extremely careful adding these diodes as I have
seen how easy it is to lift an etch.
____________________________________
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| |
| +=====-+ |
| | 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 |
| | | |
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| Mic . . |
| _ . . |
| (_= . Bat . |
| . . |
| . . |
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|__________________________________|
