Icom IC-821H (IC 821 H IC821H) transceiver mods reviews software and diagrams

   
 
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18 August 2018, 15:59 UTC 


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Icom IC-821H (IC 821 H IC821H)
IC-821H
Programming interface schematics for Icom:
Programming software for Icom IC-821H (IC 821 H IC821H) :
PDF User Manual for Icom IC-821H (IC 821 H IC821H) :
PDF Adjusments Procedures Manual with schematics for Icom IC-821H (IC 821 H IC821H) :
Schematics for Icom IC-821H (IC 821 H IC821H) :

Mods for Icom IC-821H (IC 821 H IC821H) :
    Icom IC-821H (IC 821 H IC821H) mods
    Icom IC-821H (IC 821 H IC821H) X-Band mod
    Icom IC-821H (IC 821 H IC821H) mods for extended TX/RX coverage
    Icom IC-821H (IC 821 H IC821H) Frequenzerweiterung

Icom IC-821H (IC 821 H IC821H) technical specifications :  Icom IC-821H (IC 821 H IC821H) technical specifications

Icom IC-821H (IC 821 H IC821H) mods

On this page is the rx/tx modification discribed for the ICOM IC-821h allmode dualband tranciever with photo's.

You need to locate the row of diodes on the display board, for that You need to remove top and bottom covers of the 821 (discribed in Your owners manual on page 50 and remove two screws witch hold the front of the 821 and turn the 2 other screws 1/4 loose so You can pull the front towards You (about 5cm)

Now You have enough space to carefully remove the diodes.

can You find them ? (they are SMD diodes)

Removing D101 gives You 136 - 174 Mhz (RX)

Removing D103 gives You 420 - 460 Mhz (RX)

Removing D105 gives You 136 - 174 Mhz (TX)

Removing D107 gives You 420 - 460 Mhz (TX)

And then You will have to make a choice: leaving the D102 diode in place for 1750Hz tone when You press the tone button on the front, or if You remove D102 You can use the subaudio tones (like the ones used at some european repeaters) but no 1750Hz tone.

If this is Your first attempt to solder annything I would suggest to leave it untill You have alot of practice, make sure You have a small soldering tip and some pliers then gently heat one side of the diode and lift that side up, I would suggest leaving the diod hanging there (only connected to one side) in case You want to restore the 821h to its original state.

I removed ALL diodes so now I have RX/TX 136 - 174 Mhz and RX/TX 420 - 460 Mhz and subaudio tones.

On this photo You can see were the diodes used to be.


After I had done the mod there occured a problem, the subtone's deviation was too high because the same pot is used for the deviation of the 1750Hz burst tone in the european models, the deviation should be about 1/3 of that of the 1750Hz tone (about 0.6Khz).

If You have a second reciever just connect a voltmeter over the speaker of Your second reviever (not the 821) and note the meter readout then adjust R64 for 1/3 of the first signal (after the mod You now have a usa+ version).

Were can You find R64 ? well just look at the following photo's and You will find the R64.

Click for big view.



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