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Icom IC- 22S mods
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IC22S.3
BAND SEGMENT MODIFICATION:
The normal frequency coverage of the IC-22S (with X1=7.680 MHz) is 144.390 to
148.215 MHz, a range of 3.825 MHz (Fmax - Fmin), by 15 KHz steps. The
frequency segment covered by the IC-22S is settled by Crystal X2 (near X1 on
PLL board). Its normal frequency is: 44.563 333 MHz. The lowest frequency
(Binary code 00) and the highest frequency (binary code 255) covered by the
radio with a given crystal (X2) is calculated this way:
Fmin. = (Xtal freq. x 3) + 10.7 MHz
Fmax. = (Xtal freq. x 3) + 10.7 MHz + (RANGE)
RANGE = (X1 / 2) - (X1 / 512)
Example:
Fmin=(44.563 333 MHz x3) + 10.7 MHz=144.390 MHz
Fmax=(44.563 333 MHz x3) + 10.7 MHz +((7.68 MHz/2)-(7.68 MHz/512))=148.215 MHz
As I said before, the normal coverage of the IC-22S is 144.390 to 148.215 MHz
(With X1=7.680 MHz). The 215 KHz Higher than 148.000 are useless and limits
coverage in the low portion of the 2 meter band. Changing X2 by a 44.488 333
MHz crystal will make the IC-22S covering from 144.165 to 147.990 MHz (15 KHz
steps).
Fmin = (44.488 333 x 3) + 10.7 = 144.165 MHz
Fmax = (44.488 333 x 3) + 10.7 + ((7.68/2)-(7.68/512)) = 147.990 MHz
An interesting modification is to change X1 for a 5.120 MHz crystal, allowing
a 10 KHz step, and change X2 for two appropriate crystal, each one allowing
2 MHz coverage.
With X1=5.120 MHz, replacing X2 by a 44.923 333 MHz crystal will give the
following coverage:
Fmin = (44.923 333 x 3) + 10.7 = 145.470 MHz
Fmax = (44.923 333 x 3) + 10.7 + ((5.12/2)-(5.12/512)) = 148.020 MHz
With X1=5.120 MHz, replacing X2 by a 44.250 000 MHz crystal will give the
following coverage:
Fmin = (44.250 000 x 3) + 10.7 = 143.450 MHz
Fmax = (44.250 000 x 3) + 10.7 + ((5.12/2)-(5.12/512)) = 146.000 MHz
These two crystals could be installed with a switching device, to use one at a
time. This allows fuull coverage of the 2 meter amateur band (144-148 MHz),
in 10 KHz segments. Local oscillator can be slightly detuned to allow
operation on 5 khz steps (146.745 MHz, example). I have not worked on it yet.
If you do it successfully, let me know!
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