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Hello again, Another question, has anyone here used an HP 3575A Gain Phase Meter (1Hz - 13MHz) to set their Rubidium to match the GPS sourced 10 MHz clock? Would that method be more accurate to line the Rubidium up than using a 12 digit frequency counter clocked off of the GPS? Signed, time newbie Chris KL7FB > Message: 4 > Date: Thu, 27 Sep 2007 06:45:28 -0700 > From: "Richard (Rick) Karlquist" <[EMAIL PROTECTED]> > Subject: Re: [time-nuts] time-nuts, frequency counters > To: Discussion of precise time and frequency measurement > <[email protected]> > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > >>> The simple answer, is it introduces another place for drift >>> to occur. If the power supply that provides the current to >>> create the C-field drifts with temperature, component aging, >>> power line voltages, phases of the moon, ... your reference's >>> frequency will also drift. >>> >>> -Chuck Harris >>> >> I must be missing something. Aren't all those bad things going to happen >> whether you adjust >> the C-field or leave it untouched? Isn't the C-field required for the Rb >> to work dependably >> and on freq? I think the question pertains to Rb sources that already >> have a screw to make >> the adjustment. Maybe you are saying the screw is there to put the >> C-field back where it belongs. >> I would have no way of knowing how to tell if it was right or wrong >> other than frequency. >> >> Rick said it is not a good way to adjust the frequency. I don't really >> understand why exactly either. > > There is an optimum range for the C-field. Too little will result in > insufficent Zeeman splitting and too much makes the frequency too > sensitive to magnetic field. Remember that frequency is proportional > to the SQUARE of the C-field intensity. The C field screw is not > designed to "put the C-field back where it belongs" but rather to > move it away from its comfort zone to pull the frequency. I'm not > an expert on Zeeman splitting, but I have heard people talking about > finding a setting to avoid any spurious lines, as if the setting was > like finding a clearing in a forest of lines. > > It is true that an adjustable C-field has the potential to drift more > than a fixed C-field, but this is only one issue, that may or may not > be pivotal. Another issue with changing the C-field is that it may > affect the magnetic hysteresis in the magnetic shields. > > With a synthesizer, you introduce no drift due to adjustability, you > always operate at the optimum C-field value, the adjustment is linear > and predictable, and the range of adjustment is not limited, so you > can introduce any offset you want, and it is remotely, digitally, > programmable. And with modern synthesizers, this capability may well > be virtually free. Even the HP10816 Rb standard, designed in the > 1970's, had a synthesizer that we set to get on frequency, however this > synthesizer was not intended to be user programmable. > > BTW, "C-field" is a bastardized term borrowed from cesium beam > technology where there were "A" and "B" magnets to select the state > and the C-field to bias the magnetic field in the interaction region. > Hence "A-field" "B-field" and "C-field". Of course, Rb standards have > no A or B fields. It is sort of logical in an "inside baseball" sense. > > Rick Karlquist N6RK > > > > ------------------------------ > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > End of time-nuts Digest, Vol 38, Issue 38 > ***************************************** _______________________________________________ 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.
