[Lowfer] BPSK31

[Ed Phillips]

Stewart Nelson wrote:
> 
> Hi Ed and all,
> 
> Some possible ways to generate PSK31 at LF with little hardware:
> 
> 1. Use the serial port at a relatively high baud rate to control the timing.
>    For example, set it to 9600 bps, 8 data bits, 1 stop bit, no parity.
>    To send a "1" bit, send 31 characters of 0xFF. To send a "0" bit, send
>    31 characters of 0x00.  On every fourth bit, send it only 30 times
>    instead of 31.  This gives an average bit time of 32.03125 ms, within
>    0.1% of the nominal value.  The start and stop bits, which you cannot
>    control, will cause glitches of about 100 us every millisecond.  Use a
>    simple RC filter (time constant ~0.5 ms) between the Tx data line and
>    the gate that controls the carrier phase.
> 
> 2. Use the sound card for timing.  For example, generate a .wav file with
>    32 ms of a 2 kHz tone for a "1", and 32 ms of silence for a "0".  A
>    rectifier and trivial filter on the sound card output will provide the
>    needed phase control signal.
> 
> 3. An exciter like TAG, but do the audio phase shift in software, using
>    the stereo outputs of the sound card.
> 
> 4. As above, but use a 4052 mux as an image reject mixer.  Feed the two
>    address lines with quadrature carrier signals.  These can be generated
>    by a dual flip-flop clocked at four times the desired frequency.  Now,
>    if the soundcard channels are I and Q, the four analog inputs should
>    be +I, +Q, -I, -Q.  You can use op amps for the phase splitters, or
>    use both muxes in the 4052 package, with a transformer coupled output.
> 
> 5. Generate the PSK audio at a high frequency, e.g. 18 kHz, at a 48 kHz
>    sample rate.  Combine with carrier in a double-balanced mixer.  If
>    you are trying to Tx on 185 kHz, your LO would be at 167 kHz, so the
>    image is at 149 kHz.  This is far enough away from the desired output,
>    that one high-Q tuned circuit should be an adequate filter.  The
>    second filter is your antenna :)
> 
> Hope one of these works for you.  If you have a choice, options 3-5 can
> also generate Jason, DFCW, and other not-yet-invented signal formats.
> The first two are limited to BPSK modes.
> 
> 73,
> 
> Stewart KK7KA

Steward:

	Thanks to you (and all the other guys who responded to my question).
I'm completely "sound card illiterate".  How do you generate the wave
file and how do you arrange the L & R to be in quadrature?

	Another question.  Is the PC timing accurate enough for the various
BPSK modes without trying to use an external clock as well?  The only
thing I know how to program is QBasic.  I've gotten as far as writing a
program which will generate the varicode for the various characters and
output it from the serial port but have never been sure about the timing
accuracy.

	I like your options 3-5.  Doesn't sound like much stuff to build, so
the problem is how to get the right stuff out of the sound card.  Are
you saying that the present sound-card programs can generate that high
an audio frequency?  Will have to try that here and see what happens.

Ed