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 <[email protected]> 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 <[email protected]> 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? >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
