On Mon, May 29, 2023 at 08:55 AM, loopMasta wrote:
I get 12v at the cathodes of? D30 and D31 ???
To check Q29, I would verify that the gate is close to the input voltage to the sBitx when receiving and close to zero when transmitting.
Q29 gate is 0v
LoopMasta,
The voltages you listed do not make sense.? A zero volt on the Drain of Q28 and 12 volts on the diodes would mean that L27 is open.? Can you verify that there is continuity across L27?
At the same time, you state that there are 0 volts on the Q29 gate when receiving.? That means that Q23 is shorted or grounded.? This would turn off Q28 and allow the drain to rise to 12 volts.
Your issue is that the Pin Diodes are not turning on to let the RF through to the receiver.? When the diodes are on, the voltage on the cathode (banded) end should be zero volts to turn on the diode.? When the diode is in forward conduction mode, it allows the RF signal through.
| Sbitx T/R switch truth table |
? |
| ? |
? |
? |
? |
| ? |
Receiving |
Transmitting |
? |
| Q22 |
Off |
On |
? |
| Q23 |
Off |
On |
? |
| Q28 |
On |
Off |
? |
| Q29 |
On |
Off |
? |
| ? |
? |
? |
? |
| When On the drain should be close to the source voltage |
| When Off, the drain should be much higher than the source voltage |
| The Gate voltage needs to be higher than 2.5 volts to turn on the MOSFET |
Check that the TX signal is at 0 when receiving and that the Q23 drain is at 12 volts,?
73
Evan
AC9TU
