A Digital LCD Makeover For An Analogue CRT Spectrum Analyser

[Seb Holzapfel, VK2SEB] has a rather nice spectrum analyser, a Hewlett Packard 141T. It’s an entirely analogue instrument though, so it lacks some of the sophisticated features you might expect to see on its modern counterparts.

One feature the HP does have is a vertical deflection output that in effect allows the trace to be reproduced on an oscilloscope. [Seb] has taken that and applied it to an STM32F746 Discovery board with its associated LCD touchscreen to produce an interface for the HP that includes modern features such as trace normalisation and a waterfall view. Along the way he’s had to make a voltage level converter to render the HP’s scan output into a range acceptable for the ST board.

He goes into detail on his software for the project, which he is at pains to remind us is still very much a work in progress. He notes that the HP has a range of other outputs (on those “D” sockets that include co-axial connectors) that provide information about its band and scan settings, so there is ample possibility for further customisation.

If you are interested in this project then the code is all available via GitHub, otherwise you can watch his video below the break. He’s labelled it as “Part 1”, so we look forward to more on this project.

If [Seb] sounds familiar to you, that may be because we recently featured his prototyping of microwave stripline filters.

8 thoughts on “A Digital LCD Makeover For An Analogue CRT Spectrum Analyser

  1. Now this is interesting.
    I too have a HP 8555A and I was thinking about something along the same lines, but for transferring hard copies to a computer.

    Yet to find the preselector option for cheap nor the tracking generator.
    I’ll likely have to build the tracking generator myself.

  2. I find this interesting, but clickbaity, should be “LCD add on” I thought wow, replace the crt with LCD, convert the analog deflection signals and put on LCD, cool. Instead I was like oh, it’s a spectrum front end output to LCD, why not just make your own front end instead?

    1. Replacing the screen shouldn’t be that hard, he already has all the needed signals. I would try sampling them using an Ethernet capable board, so that they can be transmitted locally and shown on a bigger window, used for calculations etc. Adding markers on the PC side then would be a nice touch.

  3. Wonderful video on a lovely piece of vintage equipment.
    It’s almost plasphemy to put the output of the 141T into a cheap plastic Rigol scope.
    Beautiful video editing and none of that slow mousey pointing stuf on his big PC :)
    Even his DaveCad has style.

    But I can’t keep from wondering…
    How does this display project compare with (probably PC based) displays of other Open Source spectrum Analyser projects? It would be nice to see some cooperation and see this display mated with OS hardware someday…

    I foresee a great future for Seb.

    About Ethernet:
    At 1m30s, lower right from the middle of the discovery board shows “Ethernet”.

  4. The good: Finally an alternative to resurrecting HP SA displays.

    The bad: The life of the LCD displays will last one-tenth of the lifespan of the original CRT displays (after possible recapping of-course). Then they will be irreplaceable.

  5. I am very excited to see this as I too have been considering this! I have an 8591A, and look forward to adapting your system to my analyzer. Keep up the great work! I have installed ready made mods to the 85xx series, but I was very unimpressed with their abilities.

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