Andre
Now I know your location. So your questions make more sense to me.
With respect to home brewing atomic standards. There have been numerous
threads on time-nuts around this.
The fact is technology has obsoleted so many technologies that things like
Rb references can be had far cheaper used then home brewed. Or GPSDOs very
cheap and there is almost always a way to sneak an antenna outside. Just
have to work at it. (Been there, done that)
H masers are even more complex and again search time-nuts for details.There
have been really good threads on rebuilding used H Masers. Wow complicated!

So all of my comments are useful but the real question is what do you want
to accomplish? A good reference for your SDR. Build an atomic standard for
fun. Nothing wrong with any of these. But useful to understand your goal.
Regards
Paul
WB8TSL

On Tue, Apr 11, 2017 at 3:31 AM, Andre Andre@lanoe.net wrote:

On Tue, 11 Apr 2017 07:31:01 +0000
Andre Andre@Lanoe.net wrote:

Building my own Rb vapor cell standard or H-maser is on my list
of Things-I-have-to-do-before-I-die :-)

If I had to do one of those now, I would go for a Rb vapor cell
with dual-resonance using an external cavity laser diode for pumping.

The electronics for such a thing are relatively easy, if you are not
afraid of Jiga-Hurts and using these pesky QFN packages. But it isn't
cheap either. There was a discussion started by Bert[1] where I ventured
a rough calculation what I think it wold cost. Though I think I have
understimated the cost of an ECLD (it's more like 1k-5k from what I have read)

			Attila Kinali

[1] search for "thinking outside the box" in the archives

--
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

On 4/11/2017 12:31 AM, Andre wrote:

Not a DIY project, but I was the RF designer on the HP 10816 rubidium
standard, which never made it to product introduction (a half dozen
working pilot run units were built in 1982).  I would say this task is
probably beyond the scope of a DIY project, at least for most
time-nuts.  The Rb lamp drive circuit (particularly getting the
lamp to light up) is very challenging.  The step recovery diode
multiplier is very challenging.  The photodetector and loop
integrator is non trivial.  The synthesizer is the one thing that
is easy in 2017.  The oven is also no simple thing to get
low tempco.  Unlike a crystal, you have a lot of heat being
generated by the lamp, etc. The lamp needs to be at a different
temperature than the other cells.  You have to keep the tip
off at the lowest temperature to keep the Rb in place and not
"flood" the cell and block the light.  Etc., etc.

This is in the category of projects where if you were qualified
to do it, your time is far too valuable to do it for the amount
of money you would save.

Rick N6RK

On 04/11/2017 05:54 PM, Richard (Rick) Karlquist wrote:

Probably right.

There would be none. It would be replaced by a laser. That has its own
set of "problems" but different.

Today you would not go the SRD route in synthesis.
Besides, SRDs can be hard to find these days.

I'd expect the loop integrator to be done in digital, which eases up on
some of the design problems.

Indeed-

Going down the laser-route, the balance of temperature between the cells
is no longer a relevant problem. Further, the lamp and its heat is gone.

You still have this problem, but not as a lamp problem but only for the
resonance cell part.

This is the type of project you do not to save any money, but to spend
and learn.

Even if done in a much more modern fashion, avoiding several of the
traditional problems, there is plenty of issues to solve and handle.

Cheers,
Magnus

Hi

If you are going to do a Rb, probably the best place to start is with a salvaged physics
package out of one of the telecom Rb’s. That would let you get the “easy bits” worked
out on your side of the design. It would also let you lear how to address  a few of the
more complex items sorted as well. Since the salvaged physics package performance
is likely better than what you would build in a basement, the performance of your device
would not be impacted in a negative way. Indeed it’s “cheating”, but it’s about the only
way to move the project forward.

I agree with Rick that Rb is by far the easiest one of the atomic devices to address. The complexity
of the device / design precision goes up quite a bit for the other candidates. To the degree
that Rb is complicated, it’s quite easy compared to the others. One way to view this is to
take a look at the minuscule size of the resonance response above the noise floor on even
a well made standard ….

Bob

YES SDRs [step Recovery Diodes] is hard to find today, but there many--
PIN -- diodes, which exhibits that effect, even some standard rectifier
diodes could be used for, despite of that Magnus is right, today are
better solutions available e.g. PLLs with 10GHz prescalers

73

KJ6UHN

Alex

On 4/11/2017 9:22 AM, Magnus Danielson wrote:

the are 6GHc synthesizer chips from ADI available see here
http://www.analog.com/en/analog-dialogue/articles/design-a-direct-6-ghz-local-oscillator.html

73

KJ6UHN

Alex

On 4/11/2017 8:29 AM, Attila Kinali wrote:

On 4/11/17 9:22 AM, Magnus Danielson and Rick Karlquist wrote:

I would agree, after watching the folks in my area doing the Cold Atom
Lab (which makes Rb Bose Einstein Condensates in a "benchtop" unit) here
at JPL. It's similar in many ways to building a Rb reference.. lasers,
Rb cells, etc.; countless things to do, to figure out, and none of them
are easy.

When I read about the frequency generation in the Rb or CS there are
normally many numbers associated with the actual frequency. Down to at
least the 1 Hz level. Many of these PLLs are intended for multi-KHz steps.
I speculate you might need 2 PLLs one thats very fine in I hz increments
that gets added to something like these PLLs that step in 200 KHz
increments.
Regards
Paul
WB8TSL

On Tue, Apr 11, 2017 at 2:32 PM, Alex Pummer alex@pcscons.com wrote:

You always want two frequency sources.  One generates a carrier
frequency offset many MHz from 6.834 GHz and the other frequency
source modulates the carrier with a sideband that is at the
exact ~6.834 GHz frequency that finds the atomic line.  The
sideband is in turn modulated with audio to find the exact
center of the line.  This is now the easiest section to
design.

This architecture automatically gives you gobs of resolution.
Of course you always have the C field for infinite resolution.
The other thing it does is prevent RF leaks from exciting the
atoms, since the strong LO is safely offset from 6.834.

Rick N6RK

On 4/11/2017 2:59 PM, paul swed wrote:

Hi

If you make the cells in the basement (or even in most factories) the ability to have a wide range
synthesizer will come in handy. The whole “6.834xxx GHz” thing is dependent on a number of variables.
It is not at all uncommon to produce cells that come out 10’s or 100’s of KHz off of the “right number”.
Wide range synthesizer = higher yield.

Bob

But it is as Richard said and after he sent it I remembered reading about
it in the "Quantum beat".
The trick is to get that accurate frequencies sideband to land on the RB or
CS frequency. Just 1 sideband. So using a large step synthesizer and then
another to get the finer detail is a reasonable way to go.
Regards

On Tue, Apr 11, 2017 at 10:13 PM, Bob kb8tq kb8tq@n1k.org wrote:

An update about this thread...

It turns out that OP (Andre) would like the readings of his vintage Black Star (UK) Nova 2400[X] 8-digit 2.4 GHz bench frequency counter to be accurate and stable to the 8th digit. That's all. The internal XO or TCXO is not good enough for that last digit or two. Not to mention the cal date is 1996.

So the good news is that he is not embarking on a life-long project to build his own atomic clock. This thread is just a newbie looking for a simple answer to an accuracy / stability / calibration question. His counter has a BNC for external timebase, so ...

I think it would help him if any UK/EU time-nuts:

• have a 1e-9 or 1e-10 level OCXO to spare -- which he would have to calibrate, or
• can help him locate a surplus telecom Rb -- inherently good enough that calibration is not even required, or
• point him to a cheap newbie-friendly 10 MHz GPSDO -- if his environment would make that possible and reliable.

I would guess that a mere 8-digits of accuracy/stability should cost no more than 100 these days. If you can help, please send him email, off-list.

Again, OP is not looking for laboratory-grade accuracy or to build his own atomic clock from scratch. It's just an 8 digit counter.

/tvb

----- Original Message -----
From: "Andre" Andre@Lanoe.net
To: time-nuts@febo.com
Sent: Tuesday, April 11, 2017 12:31 AM
Subject: [time-nuts] Re. DIY atomic "resonator"

Hi

According to the data sheet the X version of the 2400 has a TCXO in it. The “not an X” has an XO. “Setability” of the XO is <0.5 ppm and
the TCXO is rated at 0.2 ppm. Maximum resolution on the device occurs with a 20 MHz input. That gives you +/- 0.05 ppm. The 200 MHz
range is scaled by 10 and the 2.4 GHz input is scaled by 128. Neither one gives higher resolution than you get at 20 MHz. A source good
to 0.05 ppm would only degrade the device by 1 LSB. A 0.01 ppm source would be adequate to ensure the final LSB is good. Any of the
normal eBay telecom Rb’s would likely be good enough forever and ever, even without calibration. I have yet to see one that was off by

Bob