[Lowfer] PSK31 audio beacon enhancement

[Clint Turner]

Not necessarily to toot my own horn, but I have had, for several years, 
a standalone PSK31 beacon described at:

http://www.ussc.com/~turner/psk_medfer.html

This is a completely stand-alone beacon that does its own baseband 
modulation of its own RF stages, so that one doesn't end up tying up any 
rigs at all.

Two modulation schemes are possible to generate PSK31 RF:

- Baseband modulation to be applied to a balanced modulator.
- Seperate Phase and amplitude modulation to be applied to an RF output 
stage.

For the former, one simply throws the baseband at, say, a balanced 
modulator (diode ring, NE602, etc. - the former being recommended 
because it is cheap and easy to use) and one gets a clean, PSK31 
modulated signal.  The obvious disadvantage is that it must be followed 
by a bunch of linear amplification stages.

For the latter (which, in a way, resembles the "HELAPS" system used on 
AMSAT birds) one can use a highly efficient Class D or Class E RF 
amplifier stage and modulate it that way.  In this way, one could get a 
1 watt LowFER PSK modulated transmitter that was operating at 90%+ 
efficiency when at full power (losing efficiency, of course, when 
modulation was headed downwards toward zero.  This would be ideal for 
solar-powered beacons...)

Baseband waveforms are generated using a simple PWM scheme - which 
really can't be beat for simplicity in hardware.

At the moment, the software generates only PSK31, but it would be pretty 
easy to make a system to generate something else - such as PSK10 (or 
PSK1, I suppose...) or JASON, WOLF, or something else.  CW (of different 
flavors) would also be pretty easy - limited pretty much by how much 
program memory was available.  (I decided not to try QPSK because it 
generally doesn't perform all that much better than BPSK - owing to its 
rather weak error correction.)

(Just a thought...)

Clint
KA7OEI
"CT"


>Subject: [Lowfer] PSK31 audio beacon enhancement
>
>For those not on the New Jersey QRP mailing list, the project to
>which I am refering is http://www.njqrp.org/psk31beacon/psk31beacon.html
>It is a small board that uses a Ubicom SX28 with an R2R ladder to 
>generate baseband PSK31 signals.
>
>I'm looking to modify the audio beacon design--with the addition
>of a simple little daughter card--to add some more functionality.
>For one, it will gain a little EEPROM so that it can be programmed
>and not forget thing when it loses power.  Secondly, I want to make
>it more flexable so that it will do more modes.  
>
>I expect to get it to do:
>PSK31 (psk and qpsk)
>maybe slower PSK
>CW
>QRS(S)
>Jason
>DifCW (there are several kinds)
>WOLF
>
>Maybe it will do:
>MSK16
>RTTY
>  
>