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Icom IC-2A / 2AT Frequency Coverage Modification |
Mod #1:
Some of these radios were sold with only 144-148 MHz coverage (USA) or 144-146 MHz (European). This mod allows full coverage from 140-150 MHz:
Open up the radio and locate the flexible ribbon cable that connects the thumbwheel switches to the main circuit board.
At the main circuit board end of the flexible ribbon cable add a jumper at location C4. There should already be a jumper at location C2.
At the thumbwheel switch end of the flexible ribbon cable remove the jumper which connects C3 and COM.
Reassemble the radio. Coverage is now 140-150 MHz which will handle most MARS and CAP monitoring needs. Note that the repeater offset is still 600 kHz which no MARS or CAP repeater uses...
Mod #2: This goes along with #1.
To add a strange offset mode for CAP or MARS or an odd offset ham repeater just disconnect the high / low power switch wiring and jumper the radio for high power. Wire the simplex selector lead to the armature. Connect the simplex crystal lead to the "Low" side of the switch. Connect the new crystal of the proper freqency to the "High" side. If you need a second odd offset just replace the 2‑position High / Low switch with a replacment 3‑position switch and wire appropriately.
Mod #3:
If you have studied the schematic diagram for this radio, you will notice that pins 15 and 16 are missing from the programmable divider chip IC1 (TC9122).
By simply connecting pin 15 thru a switch to pin 1, you will be able to move the radio up in frequency by 10 MHz. I suggest that you duplicate the decoupling resistor and capacitor circuitry that is on the other divider pins. If you replace the volume control with one from an IC4AT (which has a power switch) and relocate the power switch wiring to the new control this leaves the old on/off switch for use as a Normal / +10 MHz switch.
You will have to adjust L3 to find a "sweet spot" that will allow operation in both 144-148 and 150 MHz spectrum.
To do this you will have to activate the +10 switch and dial up a known active frequency (or use your scanner local oscillator as a signal generator) then adjust L3 until PLL locks up and radio begins receiving (you need an active frequency to tell when this happens). Power the radio off and on and make sure that the adjustment is stable.
You will find that if you adjust L3 to allow 2 meter reception that you will only have the bottom end of 150 MHz available. As the author was interested in monitoring several frequencies in the 151 MHz range that is as far as his modificaton went. Specifically he was looking to monitor 151.505, 151.625, 151.640, 151.700, 151.760, 151.820, 151.880, 151.940, and 151.955 MHz (all business frequencies). Note that the transmitter is emabled on these channels as well, but that it is illegal to talk on those frequencies with this radio (it is not type accepted for commercial frequencies).
Mod #4:
CTCSS (PL or CG) Tone encode: A Communications Specialists SS-32SMP or SS-64 tone encode
board will fit inside the 2AT, 3AT or 4AT, and you can cut (carefully) a rectangular hole
in the back of the radio with the DIP switch can poke through the hole. The SS-32SMP board
uses 5 bits to select 32 tones, you can fit a 6-bit switch in the hole and use the 6th
switch as tone encode on-off, just route the audio output through that 6th switch.
Com-Spec's writeup using the SS-64 with the IC2AT is here,
the SS-32SMP or TS-32 connects very similarly. The Com-Spec page at this web site has the downloadable documents on the individual boards.
Johnny Siu VR2XMC used an SS-64 and his writeup is here.
Disclaimer:
Remember - Repeater-Builder is NOT responsible for anything YOU do.
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This page last updated 10-Aug-2005
The information presented in and on these conversion pages is © Copyrighted 1995 - (date of last update) by Kevin Custer W3KKC and multiple originating authors.