[time-nuts] Re: Proposed HP-117A Modification Board

[Matt Krick]

Status Update:

It turns out the MC1496 is actually quite sensitive and really doesn't like
seeing a 60 volt peak to peak signal from the front end or a 30 volt square
wave.

So after adding some 100K resistors in front of the 1K level pots and
increasing the op-amp gain to 10, I was able to get the mixers happy enough
to get what appears to be a phase lock using a function generator.

But the square wave mixer gives me sawtooth on the output when it balance,
not sure if I nuked it with excessive signal level or it it's op-amp
voltage skew.

It seems to work but I'm not really happy with it and thinking about using
a 1:1 SMPS transformer and diodes to make a doubler for the RF side may try
the same for the reference or some sort of doubler based on a XOR gate and
transistor buffer.

On Sun, Apr 16, 2023, 22:39 Matt Krick <dcflux at gmail.com> wrote:

> Here is the proposed HP-117A Modification Board.  The board is meant to
> sit in the open slot of the 117A and will require a little bit of rewiring
> to the back plane on the underside of the chassis.
>
> But what we have here is two MC1496s set up as frequency doublers to strip
> off the BPSK data from the front end and also the local 60 kHz comparison
> signal which will be inserted before the A3 Phase Comparitor.  There are
> also op-amps buffers that will allow additional gain as needed.
>
> Both signals will then be 120 kHz instead of 60 kHz but I believe the A3
> module should be able to work with the faster frequency and the rest of the
> unit should function as normal.
>
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