On 07/11/2011 01:37 AM, Dr. David Kirkby wrote:

For the spectrum analyzer, if dynamics and closed-in noise is dear to
you, the closed-in phase-noise becomes of interest to you. The wide
phase-noise will mostly be canceled by the bandwidth of the lock-in PLL
and replaced by the spectrum analyzers own noise.

For frequency counters it really depends. Some will just switch in
whatever you feed them and others will phase-lock to it. If you
phase-lock, then high-frequency noise on the input is mostly cancelled
by the PLL bandwidth, but for those that switch in, the full bandwidth
becomes visible. Granted, it needs to be fairly noisy to make a huge
impact on measurements. Mid-term stability (1-1000 s) is however where
most of the rubidiums should give you quite a good match regardless.

It might be worth-while to use a good low-noise oscillator locked to a
rubidium to get the mid-term stability from the rubidium and short-term
from the oscillator. Granted, there will be a noise-bump as the
cross-fade between these phase-noises occurs.

I can't recall exactly which specs the above rubidiums have. However,
some of them are more modern and have a MCU sitting there and keep some
control-loops which the others doesn't have, and added stability is to
be expected.

Anyway, now you should see how I reason with preferences and such.
Hopefully you can put it together with your equipments behaviour and
your measurement needs and then spec sheets to a suitable solution.

Cheers,
Magnus

David,

The FE-5680A is always plentiful, and a lot of them are generally mounted
on a PC board, from pulls, along with having a decent price. The main thing
is availability, which means spare parts if you need them. I also know that
I've seen these used as internal timebases for counters before on the
larger HP types.

The LPRO-101 is almost as plentiful, and where it's in a flat package,
similar to the FE-5680A, it can be internally mounted in the larger
counters.

The SLCR-101 doesn't seem to be as plentiful, but some of these are
supposed to have a new type lamp, with longer life. They generally cost a
bit more too.

The FRS-C, if I recall, are older units, and are boxy, which makes them
harder to mount in thin chassis, if you want to add them inside a counter,
etc. However, they are generally cheaper, and if you're using a home brew
cabinet, size doesn't really matter then.

I have only used the FE-5680A, myself, and can recommend it, but have read
quite a bit about the others in the past. I also think that long-life lamps
are available for most of the newer units too.

Best,

Will

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On 7/11/2011 at 12:37 AM Dr. David Kirkby wrote:

MHz

want to

as the

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Hi

The LPRO is reasonable choice. Lots of them out there and nothing about them to drive up the price. The FRS-C is a similar unit, but a bit older, I see no reason to pay more for one than an LPRO. The SCLR is a repackage of the LPRO, no reason to pay more unless you need the low height.

The FE often shows up as a 1 pps part - seller converted to 10 MHz. Quality of conversion can vary.

Bottom line, buy the one you can get for the least cash. You might get two simply to have a drop in backup. They will all need heat sinks and regulated power. I would suggest putting it in a box with some output buffering and a couple BNC's.

Bob

On Jul 10, 2011, at 7:37 PM, "Dr. David Kirkby" david.kirkby@onetel.net wrote:

On the FE-5680A, there are quite a number of versions that have that
number and look the same. Most run from one voltage input (+15V ? from
memory) but some take that and a +5V to run. Most can be tuned with
software, but the dual voltage one I got some years back -- I never
found a way to calibrate it. So the 5680A is a bit of a crap shoot
unless you know exactly what you are getting.

If I remember right the FRS-C was not very good for phase noise.

On 7/10/2011 4:37 PM, Dr. David Kirkby wrote:

On 07/11/11 01:25 AM, Will Matney wrote:

I decided to get the  FE-5680A in the end. I found a seller willing to accept
£75 (~$120) for a pair of them shipped to my house in the UK. At $60 each
(including shipping), I thought that was a fair price.

If at a later date I decide I want something with higher performance, I'll
reevaluate the situation.

I don't have a need for high absolute accuracy, but I'd like to have something
better than an HP10811A (or similar) that has not been calibrated for a decade
or two.

I've got a Kenwood TS-940S transceiver with the rare SO-1 TCXO installed.
According to the spectrum analyser, that is about 40 Hz off, but I've no idea
how much of that difference is due to the transceiver or HP10811A oscillator in
the analyser. Logic would suggest the oven should be better, but that has not
been calibrated for years, so the crystal has no doubt aged.

A non-disiplied rubidium is not state of the art, but I'd feel comfortable in
setting both the transceivers TCXO and the analyser's OCXO to the rubidium.

--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
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David,

That's not a bad price for two in good shape. They generally supply the
connector with these, with the leads cut off at about 2 inches long. I just
stripped them, and soldered new leads to them, and then used heat-shrink
over the joints. After I got mine up and running, I calibrated it with my
GPS referenced HP 5328B counter. Mine works fine, and I've had no problems
with it. It was a pull on a PC board, like I mentioned earlier. Also, if
you mount them in a good aluminum chassis, the chassis is enough for a
heatsink, or so it seems on mine. All that's really in mine is the
oscillator and a power supply, which is housed in an aluminum enclosure
made with about a 0.060" thick aluminum sheet.

What I'm intending on doing, is making some rental calibration reference's
like this, and renting them from eBay, or off the website I'm starting this
fall. I'll calibrate them each time before sending them out. Amateur radio
folks, and the small shops can't afford the high prices of cal labs, most
of the time, and I'm doing this to save on the cost. After testing this
first design, and ironing out any bugs, I'm ready to start building the
first of these in about a month.

Best,

Will

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On 7/13/2011 at 4:56 PM Dr. David Kirkby wrote:

mounted

thing

that

accept

each

something

decade

idea

oscillator in

not

in

rubidium.

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On 07/13/11 04:56 PM, Dr. David Kirkby wrote:

I should add, that is transmitting at 10 MHz, so the difference between the
analyser and the transceiver is 4 x 10^-7.

--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

I'm missing the PRS10 in this list. I have been wanting to buy one for a long time, but didn't because it has been a solution to no problem for all this time.

But now I have bought a spectrum analyzer, a Rohde & Schwarz FSIQ3, with tracking generator and lots of options. It would be nice to have a PRS10 as it's external reference. I already bought a Resolution-T timing GPS receiver to discipline it over the long term.

But PRS10 standards are quite rare lately: I think I've seen only on eBay in the past year and prices have doubled since the time they showed up in numbers. And I'm starting to doubt if it will be worth the effort. My instrument has the B4 option, for low phase noise. The specifications of the internal reference are pretty good:
Aging per day 1x10−9
Aging per year 2x10−7
Temperature drift (0°C to +50°C) 8x10−8
Total error (per year) 2.5 x 10−7
No phase noise specifications on the internal reference are specified, but a plot for the instrument overall is (http://www.livingston-products.com/products/pdf/130413_1_en.pdf).

I'm starting to wonder if connecting PRS10 as an external reference would actually improve overall accuracy, because it may introduce extra phase noise. And even if I've finally got one: How to tell it's an improvement without a reference?

Any thoughts please?

I think you are right, often the internal, free running osc will give you better results. You can use the GPS or rubidium to calibrate the internal one just before you need some more accurate absolute frequency measurements on the SA.

It will depend on what measurement you are making, and whether phase noise or frequency accuracy is more important. For day to day use, the external ref will work, except when perhaps you need to look at very close skirts, where maybe the internal alone can give you lower noise. In most cases, you don't really need either (checking a filter, EMI, radio output, etc.) but a lot of thing in this list is because we can, not because we need.  :-)

Get a real clean, low phase noise 3rd signal, measure it using the internal and external osc, look at the skirts. They might even be the same, if the limit is elsewhere in the SA signal chain.

Jose

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Robert Deliën
Sent: Friday, September 23, 2011 9:25 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Any thoughts on best rubidium?

I'm missing the PRS10 in this list. I have been wanting to buy one for a long time, but didn't because it has been a solution to no problem for all this time.

But now I have bought a spectrum analyzer, a Rohde & Schwarz FSIQ3, with tracking generator and lots of options. It would be nice to have a PRS10 as it's external reference. I already bought a Resolution-T timing GPS receiver to discipline it over the long term.

But PRS10 standards are quite rare lately: I think I've seen only on eBay in the past year and prices have doubled since the time they showed up in numbers. And I'm starting to doubt if it will be worth the effort. My instrument has the B4 option, for low phase noise. The specifications of the internal reference are pretty good:
Aging per day 1x10−9
Aging per year 2x10−7
Temperature drift (0°C to +50°C) 8x10−8
Total error (per year) 2.5 x 10−7
No phase noise specifications on the internal reference are specified, but a plot for the instrument overall is (http://www.livingston-products.com/products/pdf/130413_1_en.pdf).

I'm starting to wonder if connecting PRS10 as an external reference would actually improve overall accuracy, because it may introduce extra phase noise. And even if I've finally got one: How to tell it's an improvement without a reference?

Any thoughts please?

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