Hi,
The on-board TCXO or Option 01 OCXO is either free-running with the
calibrated DAC value or being PLL-locked to the external ref. Either of
those two 10 MHz sources will then be synthesized into 90 MHz. However,
the 90 MHz path has a pretty hefty filtering with crystal filter, so it
should be able to fairly well surpress the +/- 5 MHz sidebands on the 90
MHz carrier. There is some 10 MHz routes (10 MHz TTL and 10 MHz ECL)
going out, where the TTL end seems to end up in the time-base end, while
the ECL one ends up in the 1 kHz reference generator. Both seems to have
the necessary division by 2 which cancels any 5 MHz variation out. Seems
like on first inspection it should be relatively insensitive to 5 MHz
doubling. What is an issue is the increased white noise, but filtering
helps to bring some of that out.
There is several factors in the 90 MHz synthesis chain which should be
investigated for the environmental sensitivity (such as temperature).
Cheers,
Magnus
On 11/23/2014 03:27 PM, Bob Camp wrote:
Hi
If all the “good stuff” runs on the 90 MHz, the 5 MHz issue may not be
important at all. It’s just something to watch for. If you start seeing data in
two groups, each one 20 ps wide and separated by maybe 200 ps, you are seeing a
problem from the 5 MHz.
Running the box for a while before doing a full detailed cal is a very good
idea. It’s a bit warm inside and some of the stuff is temperature sensitive.
You want it to reach equilibrium.
Bob
On Nov 23, 2014, at 1:06 AM, Don Latham <[email protected]> wrote:
Ah. Got it finally! Doh. Just finished trying out the Morion this afternoon.
Electrically works very well. Used a 7812 to drop the +15 volts from the
option 1 ocxo, there is enough power headroom to bring the Morion up from cold
and run it comfortably. As you said, the control voltage for the original is
indeed 5 v, and can be set by the internal d/a. The output of the oscillator
passes through an emitter follower voltage adjuster and through a low-q filter
to three stages of ECL buffer and then out to the 10 MHz system bus clock.
Another path proceeds to a relay-switched divide by 2 to the phase detector so
an external 5/10 MHz source can lock the internal oscillator.
The external 5/10 MHz source proceeds to the phase detector thru an identical
buffer chain without the switched divider. The remainder of the clock
circuits is a multiplier to 90 MHz.
I'll run the autocal tomorrow and then get some jitter stats if possible. This
is an early specimen, s/n about 700 or so. I can imagine seldom used, and
sitting on standby for 20 years or so, pushing the ocxo out of tolerance.
The saga continues; I may have to look for a 10 MHz replacement on epay, there
isn't room to put in an Hp, unfortunately.
Don
Bob Camp
Hi
At least the Morion’s I have seen have 5 MHz crystals in them rather than 10
MHz. They have a 10 MHz output due to an internal doubler. Since the circuit
is not perfect, there is cycle to cycle variation in the 10 MHz. It’s way more
jitter (measured in picoseconds) than the oscillator has due to phase noise.
My concern is that a counter might be bothered by this is some subtle way.
Bob
On Nov 22, 2014, at 3:55 PM, Don Latham <[email protected]> wrote:
Hi Bob: no. cobble, not double :-) A little research has me thinking I can
easily adapt a morion. I can try it at least by starting with the morion on
an
external power supply and patching the output and control voltages in to the
sr.
The sr620 has a control circuit which apparently accomplishes your
suggestions; they claim to use the internal oscillator for short term and
"lock" it to a supplied external source for longer term. Probably has a long
time constant on the built-in phase lock to do this.
Anyhow, autocal calibrates everything except, guess what, the 10 mhz source.
Thats done separately.
So a bootup self check shows OK even if the frequency standard is way off.
Onward and upward.
Don
Bob Camp
Hi
I believe that the SR620 uses a “true” 10 MHz OCXO. I would be careful
using a
5 MHz doubled to 10 OCXO. The counter may or may not be happy with
sub-harmonic induced jitter.
Best bet at the specs:
+12V power
0-5V EFC
Sine wave out +7dbm
+/- 5x10^-9 0 to 70C
Pinout - trace what you have.
Bob
On Nov 21, 2014, at 6:59 PM, Don Latham <[email protected]> wrote:
So, I got a reasonable deal on a SR620 ho ho. Know your dealer. The ocxo
is
out of tolerance. All self tests pass with flying colors, autocal works as
well. So the best parts are OK.
Does anyone:
1) have a spare Isotemp OCXO36-53 10.000 MHz p/n 6-00051?
2) know the specs, ie the input voltage/current and the control voltage
span
and direction? pinout?
I have some Morion mv-89's and could easily cobble one in if it will
work.
Apparently a correct oscillator must be in place to use an external
source,
if
I read the manual right.
3) do we have a source for the schematics for the SR 620?
The FTS 4060 is up, pumpin' and firmly locked. At least for now. That
dealer
was not lyin'
Much thanks to all of you.
The adventure continues
--
"The power of accurate observation is commonly called cynicism by those
who
have not got it."
-George Bernard Shaw
Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail: POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com
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--
"The power of accurate observation is commonly called cynicism by those who
have not got it."
-George Bernard Shaw
Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail: POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
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and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
"The power of accurate observation is commonly called cynicism by those who
have not got it."
-George Bernard Shaw
Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail: POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com
_______________________________________________
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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