[time-nuts] strange behavior of 53230A or is the light on, but nobody in?

Bob Camp lists at rtty.us
Mon Feb 17 17:29:18 EST 2014


Hi

I have a 53230, but have not gotten around to looking at it’s PLL cleanup process.

Bob

On Feb 17, 2014, at 2:38 PM, Tom Van Baak (lab) <tvb at leapsecond.com> wrote:

> Bob,
> 
> I'm wondering if you (or any else) has measured the PLL performance of the 53230-series?
> 
> I agree it will "clean up the crud" but this assumes the ext ref is dirtier than the internal osc.
> 
> What I found instead was that if you use a good external ref the PLL actually makes it worse. This was very disappointing. The XO version of the counter performed worse than the OCXO version even with a maser as the ext reference. Did your reading of the schematic show a way to directly use the ext ref, bypassing the noisy PLL?
> 
> The other thing I found was that the ref out signal was a very polluted copy of the ref in.
> 
> /tvb (i5s)
> 
>> On Feb 17, 2014, at 7:04 AM, Bob Camp <lists at rtty.us> wrote:
>> 
>> Hi
>> 
>> If you dig into the schematics (when they supplied them … ):
>> 
>> The external reference goes into a phase detector. It’s one of those digital ones that can lock up to many inputs. You could feed 3.33333333 MHz in as a standard input as well as 0.5, 1, 2.5, 5, and 10 MHz. The internal oscillator (or an internal oscillator) is phase locked to the external input through a fairly narrow analog loop. The idea is to clean up the crud on the standard line. 
>> 
>> With no external reference, the PLL drops out and you go back to what ever the local reference is. 
>> 
>> Yes there’s a little more to it than that and no the circuit is not exactly the same on every counter HP ever made. 
>> 
>> Bob
>> 
>>> On Feb 17, 2014, at 7:55 AM, wb6bnq <wb6bnq at cox.net> wrote:
>>> 
>>> 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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