[time-nuts] time-nuts, frequency counters

[Brooke Clarke]

Hi CHazlitt:

Yes, rubidum standards drift with time.  There's usually a pot and/or an 
external fine tune voltage input to make fine adjustments.  But over many years 
the drift will excedd the capability of the pot.  The unit your have and a 
number of the modern units, like the Stanford Research PRS10, have a 
programmable divider so you can get the pot/external input back in range.
http://www.prc68.com/I/PRS10.shtml

The Stanford Research SR620 counter comes close to what you're asking for.  It 
has 16 digits and depending on mode display:
Frequency: 	GHz1, MHz3, kHz3, Hz3, mHz3, uHz3 = total of 16 digits
Time:		      sec3, ms 3, us3, ns 3, ps 3 = total of 15 digits
The digits are always in the same place, i.e. the front panel has the above 
labels directly below the digits, there are no units indicators to cause confusion.


Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


CHazlitt wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+brooke=pacific.net at febo.com RETRY
> 
> Hello,
> 
> I just joined the group a couple of weeks ago and have one remark about an 
> HP counter that I bought on ebay and also one question. The HP 5386A I own 
> incorporates a 12-character display which works out wonderfully when using 
> the 10 MHz output of a Rubidium source to clock the counter. The one I 
> bought goes up to 3 GHz but there is a less expensive version of the same 
> thing which although doesn't go to 3 Gig, has the same resolution. I found 
> this unit to be a great way to compare the Rubidium's frequency with an HP 
> GPS clock source.
> 
> I bought a Frequency Electronics FE 5680A Rubidium card on ebay too and 
> found that when comparing it's output at 10 MHz to the output of the HP GPS 
> standard that they did not agree when comparing the two using the above 
> mentioned HP counter (using the HP GPS as the clock for the counter). The 
> Rubidium I purchased is a few years old but locks up every time in just 
> three minutes so I know it is in good shape but yet it didn't agree to 
> the -9 on the frequency counter.
> 
> So, here is my question, do Rubidium standards drift that much over a period 
> of years to where they have to be brought back on frequency? If so, what is 
> tuned on the Rubidium to do so, C-field? I didn't touch anything on the 
> physics package of the FE 5680A but the unit has a DDS divider built into it 
> so I was able to adjust the Rubidium to agree with the HP GPS standard 
> through an RS 232 serial connection and hexidecimal inputs to change the 
> frequency of the dividers output. The divider they use can adjust the 
> frequency far finer than the best resolution of any Rubidium standard so I 
> thought that would be a good way to match the output of the GPS standard. 
> I'm new to time standards, GPS or Rubidium units and purchased it for some 
> telecom work so I'd appreciate any suggestions or comments anyone here might 
> have.
> 
> One last question in regard to counters. Is it possible, or does anyone make 
> a frequency counter which has 12 digits but only displays 1 Hz and below 
> regardless of the frequency which is fed into it? i.e. 1 Ghz reads out as 
> 1.000 000 000 00 (if on frequency) only displaying the last cycle of the 
> count down to -11 ?
> 
> Thanks for the bandwidth
> 
> 73 K L 7 Fox Bravo.