Maybe a waterjet cutter would imapct less on the shielding properties of tthe mumetal?
Bruce On Monday, January 02, 2017 12:58:55 PM Bob Camp wrote: > Hi > > > On Jan 1, 2017, at 7:31 PM, wb6bnq <[email protected]> wrote: > > > > Hello Mathias, > > > > I think you did not quite understand how the calibration process works > > with that unit. The factory procedure is to set the pot to minimum and > > then bring the DDS up to the step that produces the closest frequency > > just below the wanted one and then use the C-field pot as the final > > tweak. > > > > The "R" value is composed of a number of factors that can only be > > determined after the Rb cell is made. A number of variables, in the Rb > > cell itself, will determine the actual "ON" resonance frequency and that > > is what is programmed into the "R" number at the end of final assembly. > > > > That "R" number is actually the Rb frequency divided by 136 plus the > > upward fine tuning of the C-field pot. See PDF page 16 & 17 of the > > attached PDF operational manual for the FEI-5650. The only difference > > between all the variants comes after the Physics Package as shown on PDF > > page 16 block diagram. > > > > The "F" number is truly a 32 bit number, not just the first 8 digits but > > all 16 of them. > > > > Your problem is being able to have a frequency reference that is, > > obviously, way better then the Rb. As Cesium and Hydrogen references are > > quite expensive that leaves just the GPS satellites as the only other > > reference available that will do the job. Of course that entails more > > than just the GPS "timing" receiver as you will need some other equipment > > to help in the comparison process. Also it takes time to do many small > > adjustments to achieve that final comparison. It won't happen in just > > one day. > > > > It would probably have been better to purchase one of the Rb's that > > already output 10 MHz instead of hacking the option 58. BUT that is just > > my opinion. > This heads you down another rabbit hole. Since the 10 MHz output units sell > better than the PPS only versions, there is a cottage industry going to > convert one to the other. Parts are missing on the board to make a “proper” > 10 MHz unit. The conversion often is a bit ugly. No matter how well it is > done electrically, bashing a hole in the magnetic shield case for the SMA > is a really bad idea unless you have the proper gear to heat create it > after you are done. > > So yes, the 10 MHz version is a better way to go, but only if it came from > the factory as a 10 MHz unit ….. > > Bob > > > Good luck, > > > > Bill Houlne....WB6BNQ > > > > Mathias Weyland wrote: > >> Hello guys > >> > >> I'm new to this list. I got myself a FE-5650A Rubidium Standard off of > >> ebay. It's the "option 58" 1 pps output variant, hence I have to modify > >> the tuning word used in the DDS phase accumulator to get 10 MHz out. I > >> found a vast amount of awesome descriptions on how to do that on the web > >> and in particular on this list. One write-up that stood out was this one > >> by Mark Sims: > >> > >> http://www.mail-archive.com/[email protected]/msg13486.html > >> > >> I think I can pull this off since everything is documented so nicely. > >> However, I'm having trouble calculating the right tuning word and this > >> is why: Mark notes that the reference frequency reported by the unit is > >> the one with the C-field pot at the lowest frequency position. He gives > >> a number of suggestions on how to deal with that. Since I didn't get > >> that hydrogen maser for Christmas, the best approach seems to be "to > >> calculate the true reference frequency from the saved (minimum C- field) > >> R=reference frequency and F=divisor word and use that value to calculate > >> divisor words." I don't understand how the saved minimum C-field > >> reference ties into this calculation. > >> > >> My approach would have been to calculate the true reference frequency > >> from the saved divisor alone, ignoring the minimum C-field calculation. > >> I don't see how the minimum C-field reference frequency would help me > >> since the C-field pot is not in the min position anymore due to factory > >> tweaking. To be specific, this is what I would do: > >> > >> The unit returns the following string upon 'S': > >> > >> OK50255055.760840Hz F=2ABB5046B34A2E00 > >> > >> Now based on this, the tuning word should be coded in the first 8 > >> characters, of F, i.e. '2ABB5046'. I'm a bit confused about the > >> remaining characters being non-zero. Any documentation I came across has > >> a number that ends in 8 zeroes... In any case, 0x2ABB5046 is 716918854 > >> in decimal and the resolution would therefore be > >> > >> 2^23 / 716918854 = approx. 0.0117 Hz which makes sense. > >> > >> The physics package would then output a frequency of > >> > >> f_ref = (2^23 / 716918854) * 2^32 = approx. 50255055.809934 Hz > >> > >> This is higher than the reference given in the 'S' output, which is in > >> line with what Mark wrote. However, scaling this with the average > >> correction factor he gave yields > >> > >> f_ref * 1.000000002150 = approx. 50255055.917982 Hz > >> > >> Which is higher than what I would expect. Then again I'm not entirely > >> sure what I would expect because various errors add up in the above > >> calculation. I'd be interested in what people with more experience think _______________________________________________ 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.
