Others have posted to Chris as the original poster so I will direct my apology there.
Chris,
I needed to look at the posting message title to see that the board in question is a Rev 5.? That is an error on my part.? I apologize for my oversight.
| Low Pass Filter Diode cathode (Banded) receive voltages |
| ? |
? |
? |
? |
? |
? |
? |
? |
| Band |
? |
D1 |
D2 |
D3 |
D4 |
D5 |
D6 |
| 80 |
? |
0 |
Vs |
Vs |
0 |
Vs |
Vs |
| 40 |
? |
Vs |
0 |
Vs |
Vs |
0 |
Vs |
| 30 |
? |
Vs |
Vs |
0 |
Vs |
Vs |
0 |
| 20 |
? |
Vs |
Vs |
0 |
Vs |
Vs |
0 |
| ? |
? |
? |
? |
? |
? |
? |
? |
| ? |
? |
? |
? |
? |
Vs = Vinput to QDX less some component voltage drops
When transmitting, the forward bias supply voltage is a pulse-width modulated voltage that maintains the configured bias current in the band configuration screen.?
If the receive selection works, the transmit selection should work.? The selection is not changed during transmission.? The voltage to keep the unused filter diodes reversed biased increases as the transmitter's power increases.? Verify that the voltage doubler provides greater than the input voltage to the QDX while transmitting to keep the unused filter diodes reversed-biased.? The best way to verify is to measure the peak voltage at the input to the LPF input diode anode with an oscilloscope and verify that the voltage on C27 is greater than that voltage by at least a diode drop.
The most common problem with failing to select the filter is a cold solder joint on one or both LPF toroids.? The next most likely is that the diodes are reversed.?
I am an early adopter of the QDX, so I do not have the Rev 5 board to verify voltage.? The above is based on my Rev 1 QDX and schematic analysis.
73
Evan
AC9TU
