FT290 CW KOX Circuit
By G8MNY
This is not actually break-in but just KOX circuit.
N.B. It can only be used on the CW mode otherwise it keys up the Tx !
Only very light currents are used in these rigs for the CW and PTT Lines and also a pulse detection circuit makes some KOX circuits unworkable.
T1,T2, = BC109 (high gain NPN)
D1,2,3 = 1N4148
C1 = 1 2.2 3.3 4.7uF depending on hang time wanted
HOW IT WORKS
1/ With the Key up, T1 is turn on by 1M and D1, the 1M is high enough not to load the CW circuit. T1 on keeps T2 turned off.. PTT low, Rx Mode.
2/ On key down, D1 instantly discharges the 1uF and turns off T1. T2 is tuned on by the 10K and D3 from the MIC's +6.8V line. PTT Low... TX ON.
3/ In between key downs the 1uF starts to charge up from the 1M and if it reaches about 1V D2 conducts and T1 will turn on and state 1/ is reached. Otherwise further key downs repeat state 2/
PROBLEMS
If T2 does not operate rig properly, test PTT volts go from around 5v to 0.3V.
Adjust the 10K if needed.
If the hang time is too slow, try increasing the C1 to 2.2/3.3/4.7uF. etc
P.S. I have only breadboarded this circuit and tested it on FT290/690/790 mk 1 so far, after Andy G0FTD wanted to know how to etc, and would like comments.
73 De John, G8MNY @ GB7CIP
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