[Lowfer] Re: BPSK31 (John Andrews)

[Ed Phillips]

Clint Turner wrote:
> 
> Ed Phillips asks:
> >Question:  How is TAG generating the BPSK31 signal?  Some of out here
> >on the west coast want to try both BPSK31 and PSKAM10 on VLF but don't
> >want to go to the trouble of building an SSB transmitter.
> 
> Years ago, I tackled a similar problem:  One of many solutions is described here:
> 
> http://www.ussc.com/~turner/psk_medfer.html
> 
> The modifications to make this a Class-E LowFER BPSK transmitter are rather trivial and have been covered.
> 
> It should be pointed out that if one doesn't bother doing envelope amplitude modulation, the penalty on receive is negligible.  The "clicks" on transmit due to the abrupt phase shift will also be contained by virtue of the high Q of any reasonable matching network used on a LowFER system - unless, perhaps, one is abutted against a band edge.
> 
> To make this work on PSK10, the varicode table would need to be modified - as would some timing in the software.  I would have done this already, but it wasn't particularly high on the priority list.
> 
> Clint

Clint:

	Thanks for the note and I'll study it a lot more.  We've considered
several of these approaches already, but none of us (K7RR, WB6RIJ, or
myself understand the mysteries of PC well enough to handle the job). 
The varicode generation is simple enough if the timing is ignored; I've
already done that in QBasic but haven't attacked the timing yet.  Peter
suggested a method using an external clock but haven't gotten around to
trying that yet.  Goal was to output the required phase-modulator keying
signal from the serial port.  We can handle the transmitter part OK. 
I'd like to communicate as well as beacon, so the PIC approach is a bit
simplistic for our lofty goals.  The transmitter I'm using here is
similar to Class E, although I don't use a 50% drive signal duty.

	By the way, this little group of guys first got together when Mike
Mideke was still up in the wilderness on San Carpejo creek and using a
water-wheel driven automotive alternator for one of his power sources. 
Really neat guy!  We all used to get together for a round table on
Sunday morning and Mike used to chime in with CW and later phone. 
Although I'm about 220 miles SE of where he was he seemed to be able to
tell when I just turned on a signal generator in the basement!!!!!!!  
One summer had several QSO's with him on 181 kHz at the time he was
running the Z2 beacon. Beauty of a quiet location.

	I've had my "IZJ" beacon on the air more or less continuously since
1976, but I sort of dropped out of things for a while about the time
Mark Mallory started his work although I used to read about it in the
Update and the Lowdown.  K7RR was much more active in CCW and similar
modulations than I ever was.

73,

Ed