Hi Jim,

On Wed, 1 Nov 2017 06:17:31 -0700
jimlux jimlux@earthlink.net wrote:

It feels like I have asked this before, but I cannot remember and
cannot find the mail....So: What do you mean by "OCXO without oven?"

		Attila Kinali

--
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 11/1/17 10:59 AM, Attila Kinali wrote:

I often have requirements for "good phase noise" but no particular
requirement for "good temperature stability" or Allan Deviation for tau

just like a GPSDO, or it can be inferred from the measurement)
I often have a system where the environment is pretty benign - a typical
on-orbit temperature variation might be a degree or two over 90 minutes
(or longer), if that - we don't know what the temperature will be (in
advance), but once it's up there, it's pretty stable.  Maybe the temp
changes a bit due to relative orientation to the sun and similar
effects, so there's a annual variation.  My current spacecraft is
expected to change maybe 5-6 degrees over the year.

For instance, in a software defined radio, the input oscillator is often
fed into some sort of NCO or DDS for tuning - knowledge of the frequency
is what you really want, because the ultimate requirement is on the
frequency accuracy at the input or output of the radio - the regulators
care not a whit what kind of oscillator is inside (well, they DO ask on
the license application, but it's really not relevant)

THere are also systems like Doppler radars - they need good pulse to
pulse stability, and low phase noise to avoid reciprocal mixing
degradation of the noise floor - but they care not what the exact
frequency is.

In general, OCXOs have crystals with high Q -> low phase noise,
especially compared to a TCXO, which can't have high Q, or the
temperature compensation circuit can't do it's work.

So, it would be nice to have a cheap lowish power packaged part that
has the Q of an OCXO, but without the power consumption of the oven
(typically measured in watts).

yeah, I'd be operating it way far from the optimum turnover temp, so
the tempco might be huge (in oscillator terms), but I don't really care

• in fact, that might give me a way to measure the temperature of the
  system.

I have gotten quotes for OCXOs with the oven disabled-  but that's
making it a custom part and as Bob has pointed out, the moment you
deviate from the "catalog part", the cost (and often more importantly,
the delivery time) goes up.

I think the ideal, of course, is to get an oscillator high performance
crystal cut with the turnover temp around 20-30C - useless for a OCXO,
but might be real useful for GPS/temp compensated oscillator where the
oscillator drives a DDS (or or provides an output giving the estimated
frequency).

Earlier this week, I put the breakout board with my NEO-M8T into an
aluminum can. The can is split into a lower half and an upper half. The
lower half was insulated on its sides internally, but open to the upper
half, which wasn't insulated. The lower area contains the NEO-M8T on its
breakout board and its matching com breakout board.

In the unusual skyview/RF environment described below:

• LH was typically showing two or three green sats, with a min of none
  and a max of five for very brief periods.
• The average dBc of the green sats was 22 dBc, with a max of 29 dBc.
• Two screen shots of LH from this time period show an Accu of 12 ns and
  33 ns.

This morning, I insulated the inside of the upper half of the can, and
added insulation to seal the top of the lower area into a chamber that
contained the GPS module board & its com board. Since then, its run for
around ten hours, same weather as yesterday except more rain, ambient
room temperature wasn't measured but is definitely warmer. Since after
around an hour of running:

• LH has been showing between two and eight green sats, typically three
  to five:
• Their average dBc is 30 dBc, with a max of 37 dBc.
• LH Accu is showing as 6 ns.

I have no idea what the temperature is inside the chamber.

As I write this, LH is showing three green sats, at 33, 34 and 35 dBc.

I expected a more stable internal TCXO in the GPS module, but I didn't
expect stronger signals. Although perhaps I should have, as the block
diagram for the NEO-M8T does show its TCXO pointing at a "Fractional N
Synthesizer" inside the UBX-M8030's "RF Block". It also shows a RTC
Crystal for a RTC inside the "Digital Block".

Is this coincidence or can reception improve with:

• a higher temperature module?
• a more stable module temperature?

I'm tempted to add some thermal mass (block of Al) to the top of the M8T
and a chunk of insulation on top of that.

Michael

p.s.
As I finish this, LH is showing five sats, 23, 30, 31, 32 & 34 dBc, Accu
6 ns

On 01/11/2017 9:55 AM, MLewis wrote:

Yo MLewis!

On Thu, 2 Nov 2017 21:54:57 -0400
MLewis mlewis000@rogers.com wrote:

I use the 'temper' to know what temp is in my GPS chamber:

https://www.amazon.com/TEMPer-USB-Thermometer-w-Alerts/dp/B002VA813U

I use that, and an incadescent light bulb, to stabilize my GPS and XO
temps in my chamber.

RGDS
GARY

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com  Tel:+1 541 382 8588

    Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin

[I hate finding unsent email in my folder :-]

Others may disagree, but I doubt that the type of small temperature variation you are referring to has any meaningful effect on tracking. While the datasheet for the M8T says that there can be "significant impact" to the specifications at “extreme operating temperatures,” it gives the operating temperature as -40 to +85 C. Simply said, if you can stand to be in the same room/space with it, I think you are fine.

Of much greater interest would be the antenna and it’s placement. I’m afraid I can’t specifically recommend a “good” antenna, but perhaps others on the list can. For my EVK-M8T, I’m using the antenna that came with the kit and it works very well. I haven’t tested other antennas with the M8T at this time, but I do have a number of other devices with antennas that work well. I also have a few antennas that work poorly with all the devices, including the ones with which they came. Unfortunately pretty much all of them lack sufficient identification markings to identify manufacture/model info.

Regarding placement, I’ve found that in a restricted area even a few inches can have a significant impact on the average number of satellites and signal level. In my case, it’s associated with the single building structure, but it sounds your case is even more restrictive. Although it can be a very lengthy process, performing antenna surveys may help improve your situation. For each location, you need to monitor the number of satellites and signal level for 24 hours or more before determining the relative merit of that location. Repeat… and repeat.. and repeat. Determining the very best location for the antenna will likely require as many antenna surveys as you have patience for. :)

Hope this helps.

Denny

Hi all

Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen
maser. From 00:00 the bare receiver board was inside a polystyrene box
where it has soaked for many months, at 16:00 I removed the box exposing
the board to the airflow in the room, including AC. The box was left off
for the rest of the day.

The green trace is temperature in the lab. The "long term undulation" in
phase is normal, although I do not know the precise cause (multipath or
something else. I am reasonably sure it is not related to temperature in
the lab.

[image: Inline image 1])

Ole

On Sat, Nov 4, 2017 at 6:06 PM, Denny Page denny@cococafe.com wrote:

Hi Jim,

On Wed, 1 Nov 2017 11:39:32 -0700
jimlux jimlux@earthlink.net wrote:

Have you tried to build your own oscillator? There are a few companies
that still sell single crystals. If you could piggy pack on some bigger
customers production, you should be able to get the crystals relatively
cheap. All you then have to do is to design an approriate, low noise
oscillator. If you can relax your frequency specs, ie if you don't care
if you are off by a few ppm, then you could scavenge the rejected crystals
from said big customer.

			Attila Kinali

--
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor

Hi

I would say there are very few companies out there that will
sell you high grade  precision OCXO crystals in single piece quantities.
I think  you would get one much quicker and cheaper by pulling it out
of an eBay OCXO. You can do good far removed phase noise with
a lot of crystals. Once you look close in, the performance of the
resonator matters. ADEV is the same issue, longer Tau’s are very
resonator dependent.

Bob