[time-nuts] Re: ammonia, cesium, masers, etc.

[ct1dmk]

I played a bit with that in the nineties (30 years ago...ouch...)
made some stuff and I think I can still find some of the circuits.

As far as I recall there are two aspects to consider.

One is "low pressure" means vacuum pumps and pressure gauges calibrated 
to ammonia (but any gauge and reasonable educated guess work will work 
too), and if we want to make a permanent cell we need seal it... glass 
or ceramic windows on the WG, plus all the rest to seal the in/out pipes
when we are happy with the ammonia pressure, otherwise it would be a 
temporary experiment. Or leave the pumps and gas inlet running...

Second is that when the pressure is not too low absorption can be 
intense but it is quite broad (thermal/collision broadening).
If we lower the pressure it will become sharper but less intense
or else we need more waveguide to get it deep enough.
Finding the good compromise is required hence the need to control the 
ammonia pressure.

I don't remember anything in the 1Hz width... If my memory serves me 
right I would say it was in the KHz region at half width, which should 
be narrow enough to know where the center is within a few Hz...


Luis Cupido
ct1dmk.


On 9/20/21 6:51 PM, Lux, Jim wrote:
> On 9/20/21 10:21 AM, Andy Talbot wrote:
>> It ought to be possible to find the resonance with off the shelf 
>> equipment
>> An ADF5355 synthesizer is capable of small frequency steps and will
>> generate up to 13.6GHz.  Use it's 2nd harmonic leakage (4th harm of the
>> VCO), there is a bit coming out at 24GHz.   If the synth  reference input
>> is derived from a 48 bit DDS like an AD9852, it can be tuned in really
>> small frequency steps, far below the 1Hz steps that ought to be enough to
>> spot the absorbtion.   Isn't Caesium about 1Hz wide ?
>>
>> For detection, an amateur 24GHx converter is close enough to use.
>> Copper water pipe that has been hammered into an oval can support TE01
>> modes reliably enough if you need to suppress polarisation rotation.
>>
>> Andy
>> www.g4jnt.com
>>
> One might want to look at the synthesizer, odd harmonics of the output 
> might be better, depending on how the synthesis chain works. For 
> instance, maybe you want to use an 7-8 Ghz synth and pick the 3rd 
> harmonic. or even better, 5th harmonic of 4.76 GHz (which is well below 
> the 5 GHz WiFi band, so there's lots of parts)
> 
> 
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