[time-nuts] pulse height

[M. Simon]

Unless your coax is unusually long it should only look like 50 ohms on the leading and trailing edges of the pulse. A rough guide is  1nS per foot. So 10 ft of coax will look like 50 ohms for 10 nS. Of course the velocity factor of the coax will lengthen that time by roughly 50% for most coax you will find around the shop. 

You might want to set up a triggered 555 (556) or some such fed into some high speed CMOS (LVC or AHC etc) to see if it is your set up or the eqpt. For starters just the 555 will give you an indication. Start with 10 or 20uS pulses at around 100 Hz and slow the rep rate down. 

Dumb question: are you using a 10X probe? Have you accounted for that? 

Simon

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Date: Sat, 24 Nov 2012 16:52:50 -0800 (PST)
From: Mark Spencer <mspencer12345 at yahoo.ca>
To: time-nuts at febo.com
Subject: Re: [time-nuts] Question re 1pps output on the Z3805A
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    <1353804770.27074.YahooMailClassic at web121001.mail.ne1.yahoo.com>
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Thanks all for the responses.  

I
 am routing the signal via 50 ohm coax to the 1Meg ohm input of a 100 
Mhz analog scope using dc coupling.  After some fiddling with the 
trigger settings I am able to observe a brief pulse every second that 
appears to be .15 volts above ground.   I'm not inclined to believe that
 the signal is actually .15 volts though.  I did try terminating the 
scope end of the coax with a 50 ohm load and the signal as displayed on 
the scope didn't change.   I recall making similar measurements in the 
past and seeing more reasonable results.    
I really don't want to 
blow the inputs on my 5370B's hence my caution here. I did try 
connecting the signal to one of my 5335B's and based on the trigger 
settings I was able to use to get that counter to trigger I'm inclined 
to believe it is  3.3 or 5 volt TTL level but I'm not 100 percent sure.
I'll
 have to do some more experimenting with my analog with other 1pps 
signal sources to gain more confidence in my measurements and or ask 
Santa for a digital storage scope (:

Regards
Mark Spencer


 



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