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  • Author Author: michaelkellett
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Two rather different communications testers.

michaelkellett

I spotted 2 Hewlett Packard 3784A Digital Transmission Analyzers on Ebay recently. I thought they might be interesting for the boxes but when I looked more closely I realised that they were a bit more interesting because they should be able to talk to an instrument I designed in 1986/6 for BT - the Tester 167C.

I acquired the 167C a couple of years ago and it sits on a shelf to remind me of when I used to design this kind of thing. BT (in those days) were still specifying their own custom built test equipment and designed several instruments for them. The 167C was one of the last we did and it was powered by a Motorola 6809 processor with all the code written in assembler. It had a CRT display and operated as low speed (up to 2Mbit/s) telecoms signal generator with a very unusual analogue narrow band measuring system which was used for testing individual signal booster/repeaters arranged in a string. We probably made between 150 and 250 of them and I think they were sold for about £350. It might have been a little more but certainly no more than £500.

The HP 3784A is a more general purpose instrument, and capable of working at higher frequencies (up to 34Mbit/s) and it was marketed world wide, although designed in Scotland I think. It was based on an Intel 8088 processor and offered a very expensive option for jitter measurement.

The 167C was released in 1987 and the 3784 in 1989. In 1990 the 3784A appears in the HP catalogue at $10200 (+ $5800 for the jitter option).

I couldn't turn down the chance to get my 167C something to talk to and I was able to buy both 3784A instruments at a very reasonable price.

Bearing in mind that all three instruments are now about 35 years old it's impressive that they all work - and the 3784A can lock on to message from the 167C. One of the 167C features is that it can inject code or bit errors into a data pattern at any rate from 1 in 10E3 to 1 in 10E9.

In the test shown in the pictures the 167C is generating a pattern of 1010 encoded in HDB3 at 2048 bit/s and injecting bit errors at the rate of 1 in 10E6.

Both instruments are based on a micro backed up with large numbers of 74HC logic chips, some static RAM and some nice analogue stuff. (The 167C has the analogue slective meter and the 3784A the jitter measurement. (Sadly my 3784As don't have jitter measurement installed.)

Although the 3784A has a nicer box than the 167C I like to think that we offered a much nicer user interface - and  a much more competitive price. But in the long run HP got all the glory Relaxed

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MK

Parents

  • Some good data points on running a business here.

    We probably made between 150 and 250 of them and I think they were sold for about £350. It might have been a little more but certainly no more than £500.

    If we take the best case in those days: 250 units sold, £500 each.
    Did this product generate a viable profit? Enough to cover R&D, BOM, production, and expected margin?

Comment

  • Some good data points on running a business here.

    We probably made between 150 and 250 of them and I think they were sold for about £350. It might have been a little more but certainly no more than £500.

    If we take the best case in those days: 250 units sold, £500 each.
    Did this product generate a viable profit? Enough to cover R&D, BOM, production, and expected margin?

Children
  • in reply to Jan Cumps

      Generally these projects broke even unless the customer bought a second batch, at which point they made a profit because the price didn't change.

    The numbers are not quite as grim as they look - since 1987 price inflation in UK has been x2.95 so 200 piece order at £425 would be a £250k order at today's prices. If I were to design the 167C now, with 1987 parts, I'd probably charge you about £90k - 110k which leaves £750 each for the build - which looks like  a viable project.

    Of course, using today's parts it could be a lot cheaper !

    MK