[Lowfer] BPSK31

[John Andrews]

----- Original Message -----
From: "Stewart Nelson" <sn@scgroup.com>
To: <lowfer@mailman.qth.net>
Sent: Sunday, June 01, 2003 01:04
Subject: Re: [Lowfer] BPSK31


> 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
>
> ----- Original Message -----
> From: "John Andrews" <w1tag@charter.net>
> To: <lowfer@mailman.qth.net>
> Sent: Saturday, May 31, 2003 8:17 PM
> Subject: Re: [Lowfer] BPSK31
>
>
> > Ed,
> >
> > > Question:  How is TAG generating the BPSK31 signal?
> >
> > It's actually a phasing SSB exciter. The carrier is generated by a DDS
chip,
> > then buffered and fed to two SBL-3 mixers. The output of my sound card
is
> > routed through a 90 degree audio phase shift network to the mixers, and
the
> > combined mixer output is amplified and sent to the PA. It's a pretty
broad
> > signal, since the PA runs in the usual lowfer switching mode. But for
this
> > application, there's nobody to bother.
> >
> > John Andrews
>
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