As a result of my e-mail message about a "QRP Inflection Point" I
received several messages wanting to know how to get on the BPSK mode.
For receiving build the Sigma-Delta circuit from QST/Jan 92 designed
by VE2IQ. You can pick up the software (Coherent version 6.0) from his
web page. http://w3.ietc.ca/home/bill/bbs.htm
For transmitting you will need a BPSK generator.
The output of the generator should be fed through a low
pass filter then to the mike input on your SSB transceiver.
The generator operates at 800 hz.
The the bpsk generator circuit is as follows:
Osc/Divider circuit - I used a 74HC4060 cmos divider with an internal
osc. The xtal required is a 6.5536 mHz series resonance available for
about a dollar. The output on pin 1 of the 4060 is a pulse at 1600 hz.
I used this signal for sync and also fed it to a squaring FF(2) to
obtain a nice signal at 800 hz. (Xtal Digikey XO18-ND)
The actual BPSK signal is generated with a EX-OR circuit 74HC86.
The output of the EX-OR is a square wave at 800 hz.
Sync FF(1) - I chose to sync the data with the clock. I wanted the
carrier to be coherent with the data pulse.
I found the osc circuit in the 74HC4060 to be voltage sensitive. So I
add a 78L05A for regulation of the power buss of the BPSK generator.
Results: I have a nice square wave with a time period of 1250.07 usec
from the 74HC86. The data is in sync with the zero crossing of the 800
hz carrier. Not bad for a couple dollars in parts. I am running the
output through a w3nqn passive filter (arrl handbook). Once you get a
decent looking output it can be feed into the S-D circuit for testing
since Bill ve2iq software is full duplex.
Squaring FF(2)
-------- -------
1600 hz ----|---------|C Q |-----------| |--- BPSK
| | | | EX-OR | output
| ----|D /Q |--- ---| | 800 hz
| | |_________| | | |_______|
| | | |
| ------------------ |
| 74HC74 | 74HC86
| |
| Sync FF(1) |
| __________ |
---------|C Q |--------|
| |
| |
Data ---------------|D |
-----------
Figure 1. BPSK Generator (800 Hz) with Sync
For receiving you can build the circuit from the QST article or purchase
a kit from VE2IQ. It takes about $20 in IC's and can be built on a RS
vector board. I think Bill currently gets about $50 for a kit with a
nice etched board and instructions. Software is free on his web page.
A plus with ve2iq's circuit, If you run the FFT.zip program (also on
the web page) and if you have only noise input to your receiver you can
geta plot (PC-CRT) of your IF bandpass filter , etc.
You should have a 368 machine with 20 mhz although some use a smaller
or larger PC to run the software (Coherent V6.0).
Have fun - The above can easily be built and tested on a weekend.
Cheers, de Stan AK0B
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