Re: [time-nuts] LED instead of discharge lamp for Rb vapor cell standards

[Bob kb8tq]

Hi

There are a number of papers on LED / Laser excitation of Rb cells (and 
other gas cells). They go back quite a ways. The gotcha (as pointed out 
in PHK’s post) is that you need to stabilize the LED source. Doing that is 
a bit complex. Doing that so that the result beats a gas lamp is a bit more 
involved than just getting it working. Part of the problem is that there are 
a number of transitions you can hit and you only want the “right” one. The
next layer is the signal to noise once you get on the right transition 

Based on the examples I have seen on my bench, the ADEV of a typical 
laser based unit is not super duper compared to Corby’s modified units. 
In defense of the designers, they normally are targeting small size rather 
than super stability. That’s what the market wants to buy …. If you are 
spending tens (or hundreds) of millions of dollars, you focus on a product 
you can sell a lot of. 

Bob

> On Feb 21, 2018, at 12:49 PM, Attila Kinali  wrote:
> 
> Moin,
> 
> Has anyone ever tried using a LED instead of a discharge lamp for Rb 
> standards?
> There are quite a few and very cheap 780nm IR LEDs available. They usually
> have a line width in the order of 20nm to 50nm (FWHM). This means that they
> still need the Rb85 filter, but they would not produce all those spectral 
> lines
> that the discharge lamp has, thus one could get rid of the (not so cheap)
> optical filter that Corby uses for the super-5065. 
> 
> The one thing I am not sure about is the filter efficiency of Rb85.
> Because now the light isn't two discrete lines from the Rb87 lamb
> of which one needs to be masked, but a continuous and wide spectrum.
> So the Rb85 "notch" filter might not get rid of all the unwanted light
> and some of this might depopulate the excited state of the Rb87
> that are in the RF cavity.
> 
> As a side-effect, you also get easier regulation of the light intensity
> of the LED, thus potentially less instability due to light-shift variation.
> Beside the LED operation being much simpler than that of a discharge lamp
> and overall less heat dissipation.
> 
>   Attila Kinali
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] LED instead of discharge lamp for Rb vapor cell standards

[Poul-Henning Kamp]

In message <20180221184928.1c9b4c3a4d2e762970b5b...@kinali.ch>, Attila Kinali w
rites:

>So the Rb85 "notch" filter might not get rid of all the unwanted light
>and some of this might depopulate the excited state of the Rb87
>that are in the RF cavity.

I have a hard time seeing how you can not get worse S/N that way.

If you want to do it with a LED, I think it needs to be a stabilized
LED-Laser.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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[time-nuts] The "NAKED" 5065A optical unit

[cdelect]

Attila,

The Child and oven windings were destroyed pulling the oven cylinders out
of the potting.

I suppose you could replicate them and try to repot but I'm never going
to try!

Cheers,

Corby
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Re: [time-nuts] LED instead of discharge lamp for Rb vapor cell standards

[paul swed]

Attila I haven't tried that and I suspect the lines are important because
that establishes the reference.
Now I would also suggest that an experiment like you suggest be tried on a
FRS-XXX cheapy Rb.
Easily dis-assembled and can be re-assembled back with the lamp. No harm.
Paul
WB8TSL

On Wed, Feb 21, 2018 at 12:49 PM, Attila Kinali  wrote:

> Moin,
>
> Has anyone ever tried using a LED instead of a discharge lamp for Rb
> standards?
> There are quite a few and very cheap 780nm IR LEDs available. They usually
> have a line width in the order of 20nm to 50nm (FWHM). This means that they
> still need the Rb85 filter, but they would not produce all those spectral
> lines
> that the discharge lamp has, thus one could get rid of the (not so cheap)
> optical filter that Corby uses for the super-5065.
>
> The one thing I am not sure about is the filter efficiency of Rb85.
> Because now the light isn't two discrete lines from the Rb87 lamb
> of which one needs to be masked, but a continuous and wide spectrum.
> So the Rb85 "notch" filter might not get rid of all the unwanted light
> and some of this might depopulate the excited state of the Rb87
> that are in the RF cavity.
>
> As a side-effect, you also get easier regulation of the light intensity
> of the LED, thus potentially less instability due to light-shift variation.
> Beside the LED operation being much simpler than that of a discharge lamp
> and overall less heat dissipation.
>
> Attila Kinali
>
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
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[time-nuts] LED instead of discharge lamp for Rb vapor cell standards

[Attila Kinali]

Moin,

Has anyone ever tried using a LED instead of a discharge lamp for Rb standards?
There are quite a few and very cheap 780nm IR LEDs available. They usually
have a line width in the order of 20nm to 50nm (FWHM). This means that they
still need the Rb85 filter, but they would not produce all those spectral lines
that the discharge lamp has, thus one could get rid of the (not so cheap)
optical filter that Corby uses for the super-5065. 

The one thing I am not sure about is the filter efficiency of Rb85.
Because now the light isn't two discrete lines from the Rb87 lamb
of which one needs to be masked, but a continuous and wide spectrum.
So the Rb85 "notch" filter might not get rid of all the unwanted light
and some of this might depopulate the excited state of the Rb87
that are in the RF cavity.

As a side-effect, you also get easier regulation of the light intensity
of the LED, thus potentially less instability due to light-shift variation.
Beside the LED operation being much simpler than that of a discharge lamp
and overall less heat dissipation.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] The "NAKED" 5065A optical unit

[Attila Kinali]

On Wed, 21 Feb 2018 15:37:53 +
"Poul-Henning Kamp"  wrote:

> I was talking about driving the single-transistor UHF generator which
> ionizes the Rb in the lamp, so far I have not even established if
> this voltage affects the HP5065 performance in the first place.

Oops... sorry, I missed that piece of context.
Yes, it is very unlikely that the noise of lamp power supply
would affect anything. At most, I could imagine that the frequency
drift of the lamp oscillator could maybe have some effects, but
even that is rather unlikely or swamped by other disturbances.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] The "NAKED" 5065A optical unit

[Poul-Henning Kamp]

In message <20180221163511.b8d6eec26415fe16e66e4...@kinali.ch>, Attila Kinali w
rites:
>On Tue, 20 Feb 2018 09:36:49 -0700
>Mark Goldberg  wrote:
>
>> I don't know anything about these devices, but for TCXOs, the power supply
>> noise significantly affects the phase noise of the output. An LM317 is not
>> well specified for noise and I expect is is orders of magnitude worse than
>> something like an LT3042 low noise regulator.
>
>It's >30dB for broadband noise, according to Gerhard Hoffmann's measurement:
>https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/

Just to point out that you are rapidly heading down a blind alley from
where this topic started:

I was talking about driving the single-transistor UHF generator which
ionizes the Rb in the lamp, so far I have not even established if
this voltage affects the HP5065 performance in the first place.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] The "NAKED" 5065A optical unit

[Scott McGrath]

WRT Rb on the envelope,  the 5065A has a built in 'cold trap' to recover the Rb 
into the reservoir,   Instructions on use are in the manual

Content by Scott
Typos by Siri

On Feb 21, 2018, at 10:33 AM, Attila Kinali  wrote:

On Tue, 20 Feb 2018 10:03:20 -0800
 wrote:

> You do NOT want to take one apart to this level!
> 
> It's never going to operate again.

Why not? Is there something you had to break to open it up this far?

   Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] The "NAKED" 5065A optical unit

[Attila Kinali]

On Tue, 20 Feb 2018 09:36:49 -0700
Mark Goldberg  wrote:

> I don't know anything about these devices, but for TCXOs, the power supply
> noise significantly affects the phase noise of the output. An LM317 is not
> well specified for noise and I expect is is orders of magnitude worse than
> something like an LT3042 low noise regulator.

It's >30dB for broadband noise, according to Gerhard Hoffmann's measurement:
https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] The "NAKED" 5065A optical unit

[Attila Kinali]

On Tue, 20 Feb 2018 10:03:20 -0800
 wrote:

> You do NOT want to take one apart to this level!
> 
> It's never going to operate again.

Why not? Is there something you had to break to open it up this far?

Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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