[time-nuts] LN RB

[John Miles]

To some extent, since JLT doesn't make the rubidium MAC module itself, they
are subject to whatever performance limitations are inherited from the OEM.
Holdover specifications don't involve thermal shocks, and the telecoms
rarely want to pay extra for performance beyond the requirements.  I agree
that this is probably not the best possible solution for environments where
significant temperature fluctuations are anticipated.  

That said, there are some pretty drastic excursions on your plot, no
question about that.  It's possible that your unit has an issue which should
be ruled out before concluding that the product as a whole is falling short
of expectations.  

As a disclaimer, I work with JLT on other products, but am not involved with
this particular one.  We used a preproduction unit to demonstrate another
product at PTTI last week, and I was actually so impressed with how well it
performed that I asked to bring it back with me for further testing.  So
while I don't mean to get in the middle of this issue, I'd suggest working
with Said offline to figure out what's really going on, for the benefit of
all concerned.  I see he's gotten back in touch with you now, so I'll bow
out of that conversation. 

Right now, the unit I brought back from PTTI is coming up on 18 hours in a
3-way test with an HP 5065A and a highly-optimized custom GPSDO, with no
signs of the misbehavior that appeared in your data.  Temperature has
fluctuated a couple of degrees under normal HVAC cycling.  I'm not making a
special effort to stabilize it, but I'm also not throwing blankets on it or
blowing air on it during this particular run. :)  Just for the record,
here's how the unit has been performing:

http://www.ke5fx.com/lnrb_18hrs_phase.png

No excursions beyond +/- 10 ns so far, we'll see how it does over the next
few days.

-- john, KE5FX
Miles Design LLC 

> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at lists.febo.com] On Behalf Of
> AC0XU (Jim)
> Sent: Monday, February 04, 2019 7:31 PM
> To: time-nuts at lists.febo.com
> Subject: [time-nuts] LN RB
> 
> John-
> 
> The LNRB had been powered on continously for several weeks prior to my
> tests. Also, the same antenna/LNA is feeding multiple GPSDOs (4 others)
> with Lady Heather connected and running continuously, and none of them
> exhibited any kind of strange behavior at the times of the anomalies in
the
> LN RB timing.
> 
> It certainly appears that Jackson Labs did not design the LN RB to be
stable in
> the presence of external temperature fluctuations. To be useful, this
seems
> to imply that it needs an external environmental temperature control.
> Furthermore, it doesn't seem to be stable near the top end of its
supported
> temperature range even when the external temperature is constant, so the
> external temperature needs to be fairly low (probably under 40C or so).
One
> application I was interested in is a low SWaP timing reference for
smallsats.
> Its sensitivity to temperature seems to make that application unlikely,
> because adding external temperature control would make the electrical
> power prohibitive, even if size and weight can be kept under control. As a
> lab reference, I expect I can implement an external temperature control
and
> it may work well enough. Overall, I am very disappointed with the product.
I
> have written to Jackson Labs about my concerns but I have not heard back
> from them.
> 
> Jim