[time-nuts] Maser 0.7 nsec jumps solved

Jim Palfreyman jim77742 at gmail.com
Wed Jun 8 21:36:32 EDT 2016

Hold your horses folks.

There is more on this tale!

To recap we put the SSR on the aircon (at zero crossing) and the jumps got
very very worse. So we turned the aircon off again (winter here - so not
really needed) and the jumps dropped, but didn't go away. :-(

So we also have a heater in the room (simple 1200W column heater) and a
temperature monitor that turns the cooling or heating on as appropriate. So
we also replaced the heating relay with an SSR and it all now seems to have
gone away.

We are now thinking that the aircon AND heating *relays* had started to pit
after years of use and so give off radio transients which managed to get in
and interfere with the extremely low (-100 dBm) signal coming from the
physics package and going into the maser electronics.

We have now run for four days with no clock jumps with both aircon and
heater on and with 0V crossing SSR relays.

"Welcome to the jungle, we've got fun and games..."

Jim Palfreyman

On 3 June 2016 at 15:00, Jim Palfreyman <jim77742 at gmail.com> wrote:

> Hi All,
> Thanks so much for your input and thoughts. It has really proved helpful
> here at the observatory.
> As it turned out we easily obtained a zero-crossing solid state relay so
> we thought we'd try it.
> And, drumroll......
> It made things so much terribly *worse* than ever before. (As predicted by
> many of you above.)
> We are going to try a SSR that switches at the peak - but we need to order
> one. So stay tuned on those results.
> There is of course the "move the bloody thing far away from the maser"
> solution which could end up being a serious option. These air conditioning
> units are small and cheap (window-type), so we are trying to find the
> cheapest solution - and if that ends up being some ducting - so be it!
> Jim Palfreyman
> On 26 May 2016 at 13:13, Andy <AI.egrps+tn at gmail.com> wrote:
>> On Wed, May 25, 2016 at 12:59 PM, Mike Monett <
>> timenuts at binsamp.e4ward.com>
>> wrote:
>> LTspice shows  switching  at 0V is the best point in  time.  ...
>> Bzzzt!  Your simulation is seriously flawed, and your conclusions are
>> wrong.  What you forgot, or may not have realized, is that SPICE's initial
>> transient solution is obtained by having the signal sources already turned
>> on (at the moment of the Big Bang) and set to their initial value, so the
>> current through L2 is limited by DC conditions.  That is not anything
>> close
>> to switching the driving voltages on.  It is having one waveform sit at
>> +169.7V DC for a very long time ('forever'), and then letting it follow a
>> cosine wave.
>> Re-run the simulation with "UIC" added to the .tran statement (.tran 50ms
>> uic) and see what it shows.  Using UIC forces the initial voltage to be 0V
>> at time=0, the start of the simulation.  That's like having the switch
>> initially open.
>> Or if you don't like that, multiply the sources by a PWL waveform that
>> starts both voltages at 0V and then switches them on, a few milliseconds
>> into the simulation, with the appropriate phase.
>> Or use an actual switch.  LTspice has a switch element you could use.
>> I guarantee you, the case with the voltage switching on at the 0V point in
>> the voltage waveform, causes greater currents.
>> The smaller surge current happens when the source is connected at the
>> moment when the current i(t) would be 0A if it were a continuous waveform.
>> For an inductive load, this happens when the voltage v(t) would be +/-
>> peak
>> (or near peak, for a real load which has both inductance and a little
>> resistance).  This condition also results in no surge, thus no L/R decay.
>> All of this might not be relevant to a mechanical system, where surge
>> current is caused by rotational inertia, rather than anything electrical.
>> Regards,
>> Andy
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