Presuming all mods for opening RX and TX are made:
- Disassemble front and back as in the disassembly instruction on this page.
- Dissassemble 2F unit from 1F unit. Unsolder the ground clips as indicated.
- After opening srews unplug the 2F unit from 1F unit.
- Locate Pin 6 of PA board. This pin feeds the gate voltage to the final. AF on this pin causes am on the tx signal.
- Solder a thin insulated wire (best wire wrap) to this pin.
- Run the wire up to the volume/chanel knob.
- Replug 2F unit to 1F unit. Resolder and fasten screw.
- Solder 10 uF /10V Tantalum as indicated on Photo +side to the wire.
- Run thin wire from - to R310/315. This connects directly to TX AF.
- Solder 1M2 resistor from whiper contacts of R313/316 to ground.
This changes power dependant of supply voltage.
Now your trx should tx with abt. 450 mW AM at 5 Volts and 1 W AM at 10 Volts. Switching between AM and FM is done via power: low means AM, high means FM. In FM the residual AM is abt. 5 to 10 percent, which makes no degradation in a FM receiver due to limiting stages. The residual FM in AM mode only broadens the signal a little bit.
To remove residual FM, a diode can be connected from the H/L (Q305) line to the connection of R308/R310 with its cathode. This blocks FM on low power. In trials with commercial am trx this was not found necessary.
Good AM can only be achieved with an ample matched antenna. A good solution is a 50 cm stiff steel wire (the inside of a bike brake) directly attached to a BNC plug, and covered with a shrink tube.
This antenna works well from 118 to 160 Mc and 420 to 450 Mc for transmitting.
The IC-T7H always opens the squelch in AM. To get rid of that I found only one solution:
- Change R200 on logic board to 47K, unsolder Pin7 of IC15 from board. Carefully bend Pin up a little, and run a thin wire to R200 (not to the ground side).
- Now switch lock to lock. Turn on Radio. Clear appears, then 0000. Switch lock open.
- Press MONI and adjust Squelch to AT (the others close it completely!).
- Press MR, or enter frequency.
The trick is, that by closing lock the EEprom is disabled, and the cpu can be cheated. The memories behave a little strange, all memories can now be switched no matter of content.
Switching on unlocked resets this situation again. Lock still works as before.
Donīt tx in aircraft band if you are not allowed to!