[time-nuts] Switching 1 pps signal

[Taka Kamiya]

I took all of the advice and made what I thought was the most sensible thing.  Not using switches of any kind at all.  Out of TICC in a case, N connector comes out as input (1 pps).  I made an external box that houses 5/10MHz to 1 pps.  They are completely independent.  No possibility for cross talks.  Inside of pps converter is a short piece of a twisted pair.  Only few inches.  

I am not quite sure about termination.  There is really no guarantee that source or target is at 50 ohms.  So reflection to some degree is unavoidable.  What I'm concerned with is, at what point it will start to affect results.  

Thanks everybody for input!  It has been quite interesting.

--------------------------------------- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

    On Saturday, July 6, 2019, 7:02:00 PM EDT, Glen English VK1XX <glenlist at pacificmedia.com.au> wrote:  
 
 Taka,

It depends on the edge rate of the driver. You wont need an 18 GHz relay.

The edge rate of the driver depends on many things, but it is likely not 
to be any faster than 1V/nS

Now in all the trimbles I worked with, the falling  edge , actively 
pulled to ground was the line with the deterministic transition time.

Using 0.35 = Btr, the bandwidth is approx 350 MHz . the likelyhood is, 
with the way things are connected, the lack of any termination from the 
single ended pps signal etc, the bandwidth is unlikely to exceed 50 MHz.

You may be well advised to atttempt to terminate the 1pps signal to 
provide a deterministic edge rate and control crosstalk and reflections. 
If you have short cables, the reflection bouncing around may cause 
jitter if the edge rate was low enough. .

However, do be mindful of crosstalk from the alternate switch contact. 
The cross talk will be extremely low for signals up to 500 MHz for a 
good coaxial relay, especially into a high Z load. The high Z load will 
permit crosstalk due to the capacitance ont he relay contacts, so 
another good reason to hold the input resistance of the load of the 1pps 
down to less than a few hundred ohms

You do have to be careful of rising crosstalk using ADG901 etc solid 
state switches . A logic multiplexer might be a good choice if the 
jitter introduced is not an issue.

glen


On 7/07/2019 4:06 AM, Taka Kamiya via time-nuts wrote:
> I am trying to come up with a viable design to encase TICC along with 10MHz -> 1 pps converter.  My plan is to share the input connector and switch in/out the converter.
>
> 1 pps, although technically a 1Hz signal, rise time and duration is awfully short on some sources.  I'm sure constituent signal will go way into RF range.  I am not capable of calculating this.  But, that means I really have to treat it as an RF signal, correct?  Otherwise, slower rise will cause error as it will cross the threshold later than initiation of the pulse.  Question is, how careful do I need to be?
> My plan is to use two 18GHz microwave relay per channel to bypass/place-in the converter.  I know this would be OK but am I over-doing this?  I also have a miniature relay in DIP size but I'm afraid it may not be sufficient.  There is not a frequency spec, and consistency may be an issue.
> Advise, please?
>
> ---------------------------------------
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
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