OK. I would still be interested to see if anyone has plots on the close
in noise profile of the Lucents. The XO part has an Efrom OCXO and I
can assume it's similar to a generic OCXO. But the RB is an unknown - I
have no idea what to expect from that.
On a separate task, one of these days I would like to build up a set of
125 & 500 Mhz sources for lab and gear use disciplined by a GPSDO 10Mhz
feed. The current source is a 125 Mhz homebrew OCXO and a pair of
doubler/amp/filter sets. I assume they are pretty clean close in but
the frequency moves around a bit more than I would like as the OCXO part
of the equation is nothing special. They drive some SDR and DDS sig
gens here in the shack so the PN is a factor as well as the frequency
accuracy.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 12-Feb-19 5:15 PM, Bob kb8tq wrote:
Hi
None of the GPSDO’s out there are great for multiplying direct to microwaves.
It’s not so much
the phase noise as all the spurs (though phase noise does vary a bit). For an
instrument frequency
source, they *assume* the input will be dirty and clean it up inside the
device. So again, pretty much
any of the gizmos likely will do ok.
As you go to longer gate times than one second, the accuracy changes a bit on
most GPSDO’s.
Just how much is a “that depends” sort of thing. If you get out around 200
seconds it’s a good
bet that your 0.1 ppb is more like 0.01 ppb.
Bob
On Feb 12, 2019, at 4:30 PM, Jeff Blaine <keepwalking...@ac0c.com> wrote:
Hi Bob,
Thanks for your comments. The highest precision thing in my lab is a 5338a and that's
only if I set the gate time to something really long so that it renders a full 12 digits
of info. Other than a "I wanna be a time nut so let's see what it will do" - I
never need anything near that in reality. So let's say what I want to be able to see is
0.1 Hz resolution on a 50 Mhz test frequency. So your 0.1 ppb is a good observation.
Do you have any thoughts on PN of the 3? Ive not found plots yet for the
Lucent boxes but know the NT I have is middling on a good day.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 12-Feb-19 9:17 AM, Bob kb8tq wrote:
Hi
Pretty much all of these big old telecom beasts are “good enough” for “typical
use”. The gotcha
is that both of those terms are very much lacking in precision. Since this is a
precision sort of
thing, that may not be ideal :)
If 0.1 ppb is good enough for what you are doing, then they all should be fine.
If you need 0.001 ppb,
then none of them are likely to do what you need to do. Between those two
limits, things like antennas,
survey locations, lab temperature, and the accuracy definition you use all get
into play. Yes, you *can*
have some unusual cases (your lab goes from -20 to +90 (F of course …) on a
daily basis. For anything
reasonable, the limits above are pretty good.
If time rather than frequency *is* the goal, then one of these GPSDO's is not
really what you want.
The time pulse output from a good GPS module is likely closer to UTC (after
some math) than the
output of the GPSDO.
Bob
On Feb 11, 2019, at 9:57 PM, Jeff Blaine <keepwalking...@ac0c.com> wrote:
I have these 3 systems operational here and wonder what is the "best" of the
sources?
The local use for the reference is as a time base for test equipment. Nothing
hyper critical in the way of end-use requirements - but after running the NT
GPSDO for a few years and watching the Lucent box collect dust, I wonder if I
have got that backward?
The lucent has a 10 Mhz output on the front panel of the RB but the XO would
need a tiny bit of modification to have 10 Mhz instead of the current 15 Mhz.
There is a lot of data on http://leapsecond.com/u/sims/gpsdo17/ but I don't see
the RFTG XO on there - which I assume is due to it's native 15 Mhz Fo vs. 10
Mhz for the rest of the field.
Appreciate any advice you may have for a (very) novice 'nut.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
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