[time-nuts] WWVB PM Time Questions

[paul swed]

Lots of questions.
The d-psk-r is intended to be just after the receive preamp. So the signal
is something like 30-100uv or -90 to -70dbm region. If you are creating a
modulator then yes -3 to-7dbm would be right. But its the current through
the diodes that control distortion. At -70 you don't need a lot of current.
You simply want them conducting solidly.
There is some loss through the flipper. My clearly written notes (Not) are
-3db in, 400 mv out. For my use I was hitting a 50 db attenuator so it
didn't matter.
.sch is the free expresspcb software. Easy to use for me at least. But
there are plenty out there today. I am sure there are better. I tinkered
with KiCAD thats a whole new world. But its time...
With respect to the 7474 yes it synchronizes the flip point. But here is
teh tricky part that I ran into. I have a really great SRS DS345 sig gen.
It has trigger out and sine out at the same time.
Trigger is a nice ttl signal. But as I discovered 4 us late. Thats pretty
large at 60 KHz. So I added a monostable to delay it to the falling edge of
the sine wave some 7.025 us. Now it does a good job of flipping at 0. So
for most others that wouldn't have a nice generator like the SRS I can
think of several approaches.

Take a 60 KHz square wave TTL run it to the clock on the flip flop. Take
that same 60 KHz and bandpass or low pass filter it to a sine wave. But
that process will add delay.

Going the other way. Sine wave to flipper square it up with a comparator to
TTL. I will bet you get the same silly delay I get. Thats life.

There are all sorts of possible BPSK modulators out there cmos analog gates
and such. They just seemed messy because you have to bias the analog gates
to 50% of the supply. Also a pure gate approach followed by a low pass
filter. It goes on and on.
Regards
Paul



On Wed, Aug 19, 2020 at 6:48 PM <rcbuck at atcelectronics.com> wrote:

> Paul,
>
> You message came in just as I clicked Send on my message. If I change
> the MC34151 to a 7474 to synchronize the 60 kHz signal, does that mean
> the phase change always occurs on the zero crossing like WWVB?
>
> Ray
>
> -------- Original Message --------
> Subject: Re: [time-nuts] WWVB PM Time Questions
> From: paul swed <paulswedb at gmail.com>
> Date: Wed, August 19, 2020 1:15 pm
> To: Discussion of precise time and frequency measurement
> <time-nuts at lists.febo.com>
>
> Alright Ray we can gang up on you with two of us.
> By the way with respect to a BPSK modulator as mentioned I did just did
> that and without any special driver chip. I used a ttl 7474 to
> synchronize
> the 60 KHz reference to the incoming data.
> Data in to D and 60 KHz to C, Q and QNot to 180 ohm R to drive the
> diodes.
> Most likely this could go to 90 ohms and perhaps allow 0 dbm in or
> higher.
> But did not need that level as I needed to drop to at least -50 db for
> the
> KD2BD receiver I am working on.
> The reason to use the driver chip in the d-psk-r is with the higher
> voltage
> I can get more driver port isolation.
> Regards
> Paul.
>
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