[time-nuts] Frequency counter questions

Bob kb8tq kb8tq at n1k.org
Tue Apr 25 16:22:24 EDT 2017


Keep in mind the previously stated limitation - Your GPSDO is only just
so accurate. If you *could* read 0.001 Hz on a 100 MHz signal in a second, 
the GPSDO would not be anywhere near good enough as a reference. Keeping
track of that sort of stuff is one reason a lot of companies train you very early
in converting everything to PPM / PPB / PPT rather than talking about Hz. It’s 
a lot easier to note that 1 ppt is past what a GPSDO will do at 1 second than 
listing out all the various fractional Hz / MHz signals that are at the limit. 


The main weak point on the 5335 is the input circuit. With the attenuator set
to 0 db, you can fry it with a 5V signal. Back when it was new and 5V TTL 
was all over the place, it was a major risk. Today it’s less of a risk, but still 
worth being aware of. An accidental connection to +12 is also a good way 
to nuke it ….With the attenuator set as you normally would for a 5V or 12V 
signal there really isn’t much risk. 


> On Apr 25, 2017, at 2:41 PM, Jerry Hancock <jerry at hanler.com> wrote:
> So the STM App note An-4776 teaches how to use an external clock and it looks pretty accurate in implementation.  I’ve read thru the code and it looks easy to implement.  Now I just need to bring another signal in and count it.  I’ll be working on some code this afternoon to implement the method. 
> I also found a 5335 for cheap and ordered it.  It was listed on eBay as being in “excellent” condition though both pictures had all the lights lit so I can only assume it is stuck in power on reset or test.  I’ll see when it gets here.
> As far as measurement techniques, if I use my scope and sync to a known signal using the trigger on my 3336, it looks like I can measure to .001hz pretty reliably.  So using the STM application, the 5335 and the scope + 3336, I should be off and running.
> I’ll report back in a few days.
> Jerry
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