[time-nuts] Rigol DS1102E down to $400

Hal Murray hmurray at megapathdsl.net
Mon Jan 2 07:42:54 UTC 2012


davidwhess at gmail.com said:
> Doesn't the Rigol have delayed sweep or is it zoom only?

It has a delayed sweep.  You can delay long enough so that the trigger event 
is not in the buffer.  After you capture a buffer, you can zoom and pan 
around in it.

If the sweep is 20 ms/div or faster, the screen shows 1/3 to 1/4 of the 
buffer so you can zoom out slightly (after you stop it).  If the sweep is 50 
ms/div or slower, the screen shows the whole buffer.

It's actually a bit more complicated than that.  If the sweep speed is too 
fast, the buffer bandwidth is the limit so the screen shows a much smaller 
portion of the window.

There are 2 buffers: 16K and 1M.  (You can pick either one.)  If you are 
using both channels, they each get half of the buffer and half of the buffer 
bandwidth.  The 16K buffer writes at 1G samples/sec.  The big buffer is half 
that speed.


> Do any GPSDOs come with a low
> jitter 1 PPS output? 

TBolt and HP Z3801A both have PPS outputs.  I assume they are derived from 
the OSC rather than directly from the GPS receiver so I expect they are low 
jitter.  Aside from reducing jitter, you have to do something like that if 
the PPS is going to be useful during holdover.

I'm looking at the PPS outputs from 2 TBolts, triggering on one.  I've got 
the scope in persist mode.  There is about 2 ns of smear on the signal it's 
triggering on, only 1 ns if I turn off the other channel.  I think that's 
just from the sampling quirks.

The other channel has smeared over 20 ns.  That's after letting it collect 
for 20 minutes.  There is a lot of low frequency wander rather than simple 
jitter.  It will probably wander father if I wait longer.

 


-- 
These are my opinions, not necessarily my employer's.  I hate spam.






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