Modifications for the ICOM - RogerK

The step produced by a given crystal is calculated this way:STEP = Xtal freq.(Hz) / 512Example: Xtal 7.680 MHz: STEP = 7 680 000 Hz / 512 = 15 000 Hz = 15 KHz.The offset is calculated this way:OFFSET = STEP x 40or: OFFSET = Xtal freq. / 12.8Example:15 KHz x 40 = 600 KHz7.680 MHz / 12.8 = 600 KHzIf you want to have a 10 KHz STEP, you need to change the crystal X1 for a 5.120 MHz crystal:STEP = 5.120 MHz / 512 = 10 KHzDoing so will make the rig operate from 144.390 to 146.950 MHz, in 10 KHz segments. However, the OFFSET will be 400 KHzinstead of 600 KHz. Repeater operation is therefore impossible, but this modification is best for PACKET RADIO operation!Suggestion: You can use a 10.240 MHz Crystal (which is common in CB rigs and electronic stores) and divide its frequency by 2with a divider. You can use the unused pins of IC6 (uPD4013C) as a divider. To do this connect pins 9 and 12 together, enteryour 10.240 MHz signal on pin 11 and you get a 5.12 MHz square wave on pin 13.If you want a 5 KHz step, You need a 2.560 MHz crystal.This modification is read 669 times.top of page19-07-1998(IC-22) Band segment modificationThe 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). Itsnormal 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 MHzFmax. = (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 MHzFmax=(44.563 333 MHz x3) + 10.7 MHz +((7.68 MHz/2)-(7.68 MHz/512))=148.215 MHzAs 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 than148.000 are useless and limits coverage in the low portion of the 2 meter band. Changing X2 by a 44.488 333 MHz crystal willmake the IC-22S covering from 144.165 to 147.990 MHz (15 KHz steps).Fmin = (44.488 333 x 3) + 10.7 = 144.165 MHzFmax = (44.488 333 x 3) + 10.7 + ((7.68/2)-(7.68/512)) = 147.990 MHzAn interesting modification is to change X1 for a 5.120 MHz crystal, allowing a 10 KHz step, and change X2 for two appropriatecrystal, 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 MHzFmax = (44.923 333 x 3) + 10.7 + ((5.12/2)-(5.12/512)) = 148.020 MHzWith 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 MHzFmax = (44.250 000 x 3) + 10.7 + ((5.12/2)-(5.12/512)) = 146.000 MHzThese two crystals could be installed with a switching device, to use one at a time. This allows fuull coverage of the 2 meteramateur 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.