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 Data
is a term that encompasses all digital modes, ranging from
CW (Morse Code) to the very latest in digital communications on our
HF bands, Packet, Pactor II and Clover.
To take part in this fascinating form of communication,
it is necessary to have an amateur radio licence, as it is not allowed
on the CB bands. Having said that, it does take place on the CB bands,
but that subject I shall cover later in the article!
CW
Radio amateurs of my era had to pass a Morse test at 12 words per minute
in order to operate on frequencies that are useful for international communications,
and CW was the first mode, and indeed the only one available, to be used
for worldwide contacts. Morse is still used extensively by amateurs and
is a very enjoyable form of digital communication. It differs from the
more modern modes in that the operator has to use his brain to encode
and decode the messages. It has been replaced in commercial circuits but
will never wane on the amateur bands. Thousands of amateurs world wide
still use CW and will continue to do so. Many contests are organised especially
for this mode and all DX-peditions use it. I hope the newly licensed who
have a meagre ability to decode CW will persevere and practice in order
to attain speeds of 25 wpm plus because they will be missing a lot of
pleasure if they don't.
RTTY
RTTY appeared in the late 1950's when teleprinters became available
in all sorts of places, mostly stashed away in junkyards. I have spent
many happy hours touring junkyards from Norwich to Chelmsford in search
of a good machine. We found them too, the Creed
7B was the most common.  It
is a page printer, very fascinating to watch working, a wondrous design
and one has to admire the person who did design it. I used one for several
years and had lots of fun. We bought them for the going price of around
£12 in those days. These machines are still available today, and
must be a good deal for the impecunious youngster, for they sell now for
around £10! They can still be used for receiving all sorts of transmissions,
from amateurs to news broadcasts emanating from Reuters. It is possible
to fit a silence cover, which makes the teleprinter less noisy, but it
is not a machine for the sitting room! However, they have little place
in the modern shack owing to the noise factor, and I suppose this has
led to their demise.
This mode is still
very popular on HF but these days the RTTY is encoded and decoded by a
Modem and computer, much quieter and not so wasteful of paper! In fact
with modern software, the modem can easily be replaced with much greater
accuracy. Again, although in essence the mode has been superseded by more
modern digital modes, it will never fade because amateurs enjoy using
it. It is still possible to work many different countries on this mode,
so the popularity is being maintained. Just take a listen on a weekend
when there is a RTTY contest and you will see the popularity of the mode.
With the advent of the silicon chip and personal computers, the days of
the machine were numbered. The late 1960's saw a progression onto displays
such as the PLX solid-state RTTY machine, a dedicated design by Peter
Martinez, G3PLX. I built and used one of these for a few years. It was
sheer heaven to operate RTTY in complete silence! In the 1970's came the
first computers onto the amateur scene, with models such as the ZX81,
VIC20, and then the much awaited BBC-B. I remember saying at that time
that we would never need more than 32k of RAM. Wow!!
The ubiquitous BBC-B machine is still in general use for data modes now,
and does a reasonable job for their age, although they will not run modern
software. They can be bought for very little money, sometimes with monitor,
disk drives and so on. In fact I had somebody write to me a few months
ago, saying that despite advertising in magazines, he had to pay to have
a load of BBC-B gear carted off to the local tip. For somebody starting
to use data modes, the BBC-B would be a very good beginning. They can
be found in local yellow page advertisers if you watch out for them.
Most amateurs use the PC now, using anything from a 286 to the latest
all-singing, all-dancing Pentium MMX machine. A PC is a good investment
for the radio enthusiast; there are lots of very useful programs that
can be put to good use in the shack and most data modes are now run in
conjunction with the sound card of the PC.
AMTOR
The next step up from RTTY was a mode popularised again by Peter
Martinez, G3PLX. This is AMTOR, and it was the first step in error checking
in amateur data modes. The transmitting station sends three characters
and then waits for an acknowledgement from the receiving station. If this
is received the next three are sent. If an acknowledgement is not received,
the three characters are sent again. The roles are reversed at changeover.
The only problem with this mode is that it is quite heavy on the changeover
relay, but the modern rig can cope quite well. This mode is also still
used a lot on the HF bands. It is very tolerant of poor signal levels
and will produce copy from a signal barely perceptible to the ear.
PACKET
By the early 1980's a group of amateurs in America, in Tucson,
were developing an amateur packet radio protocol. This was based on the
commercially available X.25 protocol. Another group in Vancouver had originated
a similar protocol, and the two groups combined their talents and produced
AX.25, the protocol that is in general use on the amateur bands today.
From the USA, it quickly spread to other countries and also to four very
interested amateurs in Norwich. I was among this group and we bought printed
circuit boards from the USA and constructed the TNC-1. We were active
by September 1984. A very steep learning curve followed and we soon adapted
the TNC to run on the HF bands at 300 bauds. HF packet was away, and we
were soon working DX on that mode. At that time, there were not many personal
computers around, and we used some old Xerox 820 CPM machines, which were
brought over to us from the USA by a very good friend, Jack, W3TMZ.
This mode is in general HF use, with many BBS running, passing traffic.
Users are generally not allowed on these BBS. They are used for the purpose
of passing amateur traffic from one country or continent to another.
Packet is a mode where a lot of information is bundled together in a "packet"
together with other information, sent to the receiving station, and again,
an acknowledgement has to be returned before proceeding onto the next
packet. There are lots of variable parameters that can be set to control
the operation of the mode.
PACTOR
More development took place, and Pactor evolved. This is a cross
between AMTOR and Packet. This mode is even more sophisticated than Packet
and although it operates in a similar way, with a hand-shaking protocol,
(as the acknowledgement form of error-correction is called) it has further
abilities. For example, it can reduce the amount of characters within
a packet ( PACLEN ) according to the success of the interchange of information
without repeats. It can also reduce power until it reaches a certain threshold
below which there is poor copy. This mode is now in general use on the
HF bands and is a somewhat better performer than Packet.
PSK31
Yet another mode developed by Peter Martinez, this has grown like
Topsy on the air. It is essentially designed for keyboard-to-keyboard
communications, much like RTTY. The name is a derivation of the mode itself,
Phase Shift Keying with a data rate of 31.25 bauds, hence PSK31. Featuring
the full ASCII and ANSI character set, it also uses error correction,
a cut above RTTY in that respect! Take a look on the used frequencies,
14.070, 21.070 and 28.070 are the most common on HF and you will hear
the PSK signals there. Again, a software program is used, something like
Digipan in a Windows environment and a sound card.
FACSIMILE
This mode is used for transmitting pictures, normally weather charts
and newspaper photographs. It is a mode that has to grab you I think.
I tried it and could not see much use for it at all. However, it takes
all sorts as they say, so give it a whirl. Again, software is the order
of the day, JVFAX is quite a popular one, and is DOS based.
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