Alan G4ZFQ <alan4alan@...> wrote:
Just a quick question,
Another, how are you proposing to do the envelope shaping?
With the QCX method. In QDX, L14 is connected to the power rail. I want to
break this connection and add a transistor there, just like in QCX. I
experimented with resistors and it seems to work -- adding a resistor
there lowers the output power.
I want to do something like this:
1. Normally, the transistor will be on and won't interfere with the normal
usage of QDX (like the L14 was connected to the power rail, minus the
voltage drop on the transistor)
2. On key-down, transistor will be quickly turned off, CAT command will be
sent (to the hardware serial port, not to the one controlled via USB) to
switch to TX
3. The mod (added MCU) will wait a little for the QDX to switch to TX and
stabilize before starting to turn on the transistor
4. The transistor will be slowly turned on and then kept on
5. On key-up, transistor will be slowly turned off
6. After the transistor is fully turned off, a CAT command will be sent to
switch to RX and then, after a predetermined time, transistor will be
turned on, so the QDX can be used as normal
If it turns out that the synthesizer isn't stable enough at the start of
the TX and the delay in point 3 is too long, I'll sacrifice the QSK and
add a delay between key-up and a CAT command to switch to RX and use the
envelope-shaping transistor to key the transmitter (QDX will be in TX mode
a while after the key is released, but the transistor will be off; it will
be switched to RX after some short time if there are no more key presses).
At least that's the plan :)
The QDX clicks each time TX is started and stopped. Starting and
stopping the tone will produce clicks.
Yes, I know. I plan to send the tone independently. The keying will be
done with a separate board with a small microcontroller, and the PC
program will just set the frequency by constantly sending the tone,
regardless of the QDX mode (RX or TX). The PC won't know whether the key
is up or down, it will just read samples (and do several things with them;
I want to do the FFT to display the waterfall and at the same time route
them to speakers through a configurable bandpass filter and maybe
automatic gain control... or maybe the gain will be controlled with CAT,
it will need to be tested especially if the hardware mod will issue CAT
commands by itself) and at the same time write samples (to set the TX
frequency).
Of course if the sound card doesn't work in full duplex mode, the whole
idea will need to be changed (my previous idea was to send the key signal
to the computer and receive the envelope-shaping start/stop signal from
it), but I want to avoid adding the PC to the keying path (if possible).
