LISTENING POST REVIEW   


			      by Terry Nunn



   Ed: This review comes with the kind permission of the AUG in Brisbane - it's
  here because it's a local product which seems to do an unusual job.


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   I'd like to tell you about an addition to my AMIGA system.  At a recent
  Brisbane committee meeting, members were told of a new kit version of Tom
  Moffat's LISTENING POST.  This is an electronics and software package which
  enables your computer to decode radio facsimile (FAX), radioteletype (RTTY)
  and morse code, from a shortwave receiver.  Tom has constructed simple kits
  for a number of computers, including the Microbee, IBM compatibles, and now
  the AMIGA.

   This kit is only available from Tom, in Tasmania, and costs $73 posted
  anywhere in Australia.  A review in the January 1991 issue of Electronics
  Australia gave it good marks and included some technical details.  I was
  inspired and duly posted the money.  A week later I received a kit of
  electronic components and printed circuit board to solder together.  The
  LISTENING POST connects to your receiver's audio output and passes modified
  information to the computer's parallel port.  Your short-wave receiver
  can't be just a normal radio-cassette player, but must be able to receive
  signals transmitted in single-sideband mode.  Like AM,and FM, this is
  another method for transmitting radio signals, and seems to be preferred by
  RTTY and FAX stations.


   Also supplied is a disk of programs, written in 68000 machine language,
  which will decode the appropriate signals.  Tom has even included text
  files, on disc, for instructions and a parts list. These, together with a
  component overlay sheet, made construction reasonably easy for an old
  hobbyist like myself.  I only had to supply a couple of connecting cables
  and a small aluminium box to enclose the kit.  The latter item would help
  to reduce the effects of interference from my AMIGA and monitor.  I've
  powered my kit from a 9 volt battery, or a small low voltage mains-DC power
  pack.  Either way, I needed to supply about 20mA of current.  As the
  interface has a small 5 volt regulator on-board, this voltage source could
  have ranged from 8 to 18 volts.

   I took a little care in soldering the few dozen components, and checking
  my work, and had the kit assembled in a couple of hours.  Now for the
  moment of truth.  I connected the LISTENING POST between my AMIGA and an
  old FRG-7 communications receiver, and tuned into a RTTy transmission.  My
  radio was set to receive upper sideband (or USB) signals, which seems to be
  the usual mode.  Lines of news from Radio Peking, in perfect French,
  scrolled up my monitor screen.  It worked, first time! On-screen FAX
  images also come out quite well with the Amiga's graphics abilities.
  Screen-sized weather maps, from Australia's AXM, look impressive as they
  unfold before your eyes over about ten minutes.  You need to make one
  adjustment of a trimmer capacitor for best reception of FAX.  I found that
  careful tuning of my receiver was also necessary for good images.

   With both modes, you can view incoming messages, or images, on your
  monitor, or save them to disk.  I've yet to track down some morse code
  transmissions (from the amateur bands, perhaps?), but it should be an
  intersting search.  This type of activity can be quite addictive.  Any
  saved files can be printed on paper with an EPSON compatible parallel
  printer.

   Results will also depend on your receiver, antenna and location.  The
  antenna feeding the receiver can make a big difference to what is decoded.
  When in doubt, opt for something as elevated as possible and feeding your
  receiver via a coax cable to reduce interference.  You're got to know where
  to find the appropriate signals, too.  But, as an old shorwave radio snoop,
  I'm quite happy so far.  The kit has provided lots of new areas to
  investigate.

   500 kits have been sold so far, at a price of $73, including p&p.
  Amiga-specific software costs $35.

   Info from:
High-Tech Tasmania
39 Pillinger Drive
Fern Tree, Tas 7054.
Tel: 002 391391


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