Weekend's finds

From: Dwight Elvey <elvey_at_hal.com>
Date: Mon Dec 4 12:28:37 2000

ard_at_p850ug1.demon.co.uk (Tony Duell) wrote:
> >
> >
> > I also got a right odd looking thing - it's a (or at least looks like a)
> > ZX81 peripheral. There's a crystal on it as well as 3 chips, 4060, 4040 and
> > 4087 and its marked 'G4IDE' or 'G41DE' on the front and 'FAX PCB' on the
>
> Those chips are all standard 4000-series CMOS (the 4040 and 4060 are
> counters, I forget what the 4087 is). Drawing out the schematic should
> take < 1 hour...
>
> > back. Since I don't believe anyone produced a FAX add-on for the ZX81 I'm a
> > bit puzzled!
>
> G4IDE looks like an English amateur radio callsign to me. I suspect this
> is some kind of amateur radio/weather (?) analogue-type fax image
> decoder, and has nothing to do with modern fax sent over telephone lines.
> Are there any connectors on the PCB (other than the edge connector to the
> ZX81)?

Hi
 Although only about 6 years ago, I thought I'd mention that
related to weather FAX, I'd wrote some software that would
convert one of the softmodems ( Cardinal and Digicom ).
You need a receiver with a BFO. It did a little simple
DSP filtering and then a zero cross detector for the FAX.
It used some freeware software, from the net, to display on
a PC. If there is any interest, let me know.
 It would make sense that on a machine without extra counters,
one might add a counter to find time between zero crossings
for the frequency detectors.
Dwight

Dwight
Received on Mon Dec 04 2000 - 12:28:37 GMT