BBC Mem 1

The ME3M/502 (BBC part number) is a sophisticated self-calibrating automatic test instrument
that carries out a whole range of tests, and presents the results on a front panel display or sends
them to a printer. It was designed by BBC engineers and made under licence for them by Avitel.
As far as I am aware Tektronix in the States marketed something similar at the time called 'The
Answer', but that was very very expensive at some Ł19,000, while the BBC box of tricks was
only somewhat expensive at around Ł9,000 (!).

And why should the BBC be inclined to go to the trouble of designing and getting a subcontractor
to make such a device? Er, well I suppose that it is pretty important for a television broadcaster
to know the actual technical standards of quality of the transmissions that they are putting out.
Just consider the hundreds (thousands?) of intervening stages in the transmission chain from the
camera in the studio to our television set in the corner. Processing amplifiers, switchers,
transmission lines, hunderds of connectors, transmitters, and goodness knows what else, all
adding their own contribution to the total noise and distortion to our 'Corrie' (a soap opera to
those 'over the seas'). In the (good) old days there was of course over the years the various
forms of the test card to examine by eye and by oscilloscope, but now that the airwaves are
packed with such wonderful stuff ('pants' is the modern word for most programmes now I think)
24 hours a day, no longer are such simple pleasures available to the engineer. So a more sneaky
way of checking things out, was to hide a special test card type signals within the actual
television picture itself, and then get a clever box of tricks to find them and to evaluate them
automatically. As it was to be a 'clever' box, you could then get it also to perhaps raise the alarm
if any problems were detected. You could even put it in an un-manned location and get it to
report by remote control if you wanted.

This instrument does all of these things and also calibrates itself before each measurement. It
then repeats many times a whole series of measurements, calculates an average reading for each
result, and then displays (or pints, or sends to a remote printer) its findings.

These special waveforms are designed to show up specific areas of performance, and allow
over 20 different television signal quality parameters to be analyzed. These include various
types of noise, frequency responses, distortions, colour quality and chroma shift, together with
the signal handling abilities of the transmission system itself.

I acquired this example for just a few pounds from their redundant stores in Elstree (now
closed). The BBC seems not to use this type of 'insertion test signal' these days. ITV and
Channel 4 still do though, so I am able to keep an eye on what they are up to. Actually, I often
find it more entertaining to 'watch' the analyzer rather than the programmes (this is much better
than drying paint). Television without the screen yer see...

Unfortunately as this is a device that needs a composite video signal to evaluate, you need a
very transparent and high quality television tuner to supply undistorted signals to it, and I have
the feeling that most of the 'imperfections' that this box detects are just inherent shortcomings in
my own modest receiver-monitor. Tektronix charged around Ł10,000 for the proper (though
single channel) tuner for their 'Answer' system, but and I have no idea what receiving equipment
the BBC used.

In addition to a 'correct' tuner, it would be nice also to find a working insertion test signal
generator, but these toys are unfortunately not the sort of things to be found on the shelves of the
local branches of Currys or Dixons.

The images above are photographs of a recent analogue television transmission (rather poor
reception where I live) taken from the screen of a Tektronix 1481R waveform monitor (see
below), and show:

Above left - The waveform of a typical composite television waveform. The arrow
indicates the approximate position where the test signals are inserted. (at
the very top of the television picture, before the teletext data.)

Above right -The imbedded test signals on lines 18 and 19.

Below -An approximate graphical representation of the insertion test signal.