Hi Mike,
The most likely answer is when you select external time base for an
input, it disables the connection for the internal oscillator. The
external input signal is probably also routed straight to the reference
output jack.
However, it would be good to read the manual, as they usually cover how
those connections work. Otherwise, perhaps someone that owns one could
provide further insight.
Bill....WB6BNQ
mike cook wrote:
Something that must be simple to explain, but that I can't get my head round.
I got a new 53230A.
When first using it, I measured my T-Bolt 10MHz using the internal 10MHz
timebase and it came up short of 10MHz, 9.999 998 5xx. I wasn't worried about
it as the counter only has a TCXO internal oscillator. So I fired up my PRS10
and after leaving that on for some time, connected it to Ext Ref. , changed to
the ext time base and measured again. This time 10.000.000.00x. Then I switched
the two references, measuring the PRS10 against the T-Bolt. Again I got 10MHz
down to the 11th digit.
All that looked good so I have been using it with either the PRS10 locked to
GPS, or the T-Bolt as the external time base.
After leaving it on (but not inactive) for a month, I did an Autocal. No
problem.
I was wondering if that would have changed the internal time base frequency,
but no, using that still gave similar figures to the above.
So at that point I decided to measure the Internal TB against my reference. So
I connected the Int. Ref. Out to channel 1, connected my PRS10 ref to Ext. Ref
In, selected the EXT time base and found that the count was 10MHz dead on?????
I don't get that at all.
in summary:
DUT against internal TB counts < 10MHz. To me that means that the internal
timebase is a bit fast. Is that assumption correct?
DUT against Ext.Ref counts 10MHz
Internal TB against Ext.Ref counts 10MHz. If my assumption above is
correct, the count should be greater than 10MHz, no?
Can anyone shed any light on that?
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