[time-nuts] Surplus Guidelines, was: Rubidium Standard

[Ulrich Bangert]

Since the question was:

> Doesn't it take a greate amount 
> of RF power to excite cold Rb?

one should mention that it is NOT cold Rb that is excited. Instead, the
whole of the resonator is heated up to give the lamp housing a
temperature of 113+/-2 degree centigrade (FRK-L maintainance manual).
This in conjunction with the RF power excites the plasma, not the RF
alone.

The plasma excitation process is quite sensible to the temperature as
well as to the excitation frequency. I had bought a FRK-L from Lehman
Scientific some years ago. When the so called 'lamp voltage' had slowly
dropped down to 7 Volts over months of use the circuitry tended to
unlock from time to time until a point when it would not lock at all
anymore.

First i thought that the physics package had reached the end of its life
and that i had to throw away this 500 US$ beauty (Lehman Scientific
price some years ago). Just because i thought that i could do nothing
wrong in that situation i started to re-adjust the heater and the RF
oscillator according to the maintainance manual. I was very surprised to
see the 'lamp voltage" rise up some 100 mV and the whole unit to work
again 'as new'. The lamp's temperature had only been off abt 8 degree
centigrade.

Because neither the heater control circuits nor the plasma exciting
oscillator design are what we would call 'precision circuits' today, i
expect a lot of old Rbs to suffer from misalignments of that kind.

Cheers
Ulrich Bangert, DF6JB   

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Magnus Danielson
> Gesendet: Sonntag, 10. Dezember 2006 23:20
> An: time-nuts at febo.com; robert at delien.nl
> Betreff: Re: [time-nuts] Surplus Guidelines, was: Rubidium Standard
> 
> 
> From: Robert_Deliën <robert at delien.nl>
> Subject: Re: [time-nuts] Surplus Guidelines, was: Rubidium Standard
> Date: Sun, 10 Dec 2006 22:12:51 +0100
> Message-ID: 
> <D891702134D46242B089F044A1C20CD1025DA6 at deuterium.delien.local>
> 
> > > > Isn't it deposited metal from the filament that blackens the 
> > > > glass?
> > > 
> > > No.
> > > 
> > > Therei is no filament.  The Rubidium lamps are excited with a UHF 
> > > field which is external to the bulb.
> > 
> > I didn't know that: How interesting! Doesn't it take a 
> greate amount 
> > of RF power to excite cold Rb?
> 
> No. For instance, on my R&S XSRM it is a fairly basic 100 MHz 
> resonance setup with a single transistor in the core. It is 
> setup such that the RF coil is also part of the resonator in 
> a LC based oscillator. It is something like 1 W, which is 
> also what the literature say.
> 
> Cheers,
> Magnus
> 
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