Re: [time-nuts] Low cost GPS module for < 100ns timestamping error
On Fri, May 9, 2014 at 10:46 AM, Tony tnuts@toneh.demon.co.uk wrote:
But isn't that only supported by 'timing' GPS modules that allow you to
specify the location? But they are rather more expensive than the common
navigation type modules - are there sub $15 modules that support that
single-satellite timing feature?
With a $15 budget. I think you are limited to the old Motorola Oncore
type. The UT+ sells for about $15 on eBay. There are two versions of the
UT. Get the timing one. These aren't to bad. The PPS one sigma error is
about 50ns and the UT runs on 5 volts. The newer MT+ version is better
but at least $30.
Does it make sense to place thermal insolation on a TCXO? It does on an
OCXO because there is a thermostat inside the device and the thermal
insulation will help the OCXO maintain a constant temperature. But a TCXO
will just run hotter. I think all you need is a box to keep drafts and
direct sunlight off the TCXO.
--
Chris Albertson
Redondo Beach, California
On Fri, 09 May 2014 18:46:05 +0100
Tony tnuts@toneh.demon.co.uk wrote:
Quite a remarkable datasheet for a low cost part - I've not found any
other low cost oscillator with either of those specifications, and even
some (most?) of the OXCO don't specify the freq/temp slope.
I'm quite sure the manufacturers have this data, but they do not readily
publish it because it is not tested for and thus not guaranteed.
Ie the manufacturers want to prevent someone from taking that data,
constructing some "specs" in their mind and blaming the manufacturer
when the circuit fails because the part didn't meet the "specs".
Usually the manufacturers are quite happy to share that data if you
ask nicely.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
On 10/05/2014 04:19, Chris Albertson wrote:
On Fri, May 9, 2014 at 10:46 AM, Tony tnuts@toneh.demon.co.uk wrote:
But isn't that only supported by 'timing' GPS modules that allow you to
specify the location? But they are rather more expensive than the common
navigation type modules - are there sub $15 modules that support that
single-satellite timing feature?
With a $15 budget. I think you are limited to the old Motorola Oncore
type. The UT+ sells for about $15 on eBay. There are two versions of the
UT. Get the timing one. These aren't to bad. The PPS one sigma error is
about 50ns and the UT runs on 5 volts. The newer MT+ version is better
but at least $30.
Unfortunately they use way too much power - 800mW maximum compared to
50mW for a UBLOX MAX-7c which are around $15. It also is specified at
50ns rms, 99% < 100ns. It appears that most, if not all, the timing
type modules are higher power as well as more expensive; unless anyone
has any better suggestions it looks like I'll have to stick to
navigation type modules.
Does it make sense to place thermal insolation on a TCXO? It does on an
OCXO because there is a thermostat inside the device and the thermal
insulation will help the OCXO maintain a constant temperature. But a TCXO
will just run hotter. I think all you need is a box to keep drafts and
direct sunlight off the TCXO.
The insulation won't make much difference to the overall temperature
excursions of the TCXO but that doesn't matter because the timing is
continually corrected by the GPS; it will however significantly reduce
the rate of change of temperature thus reducing the timing errors during
holdovers when GPS is temporarily unavailable.
I might need to allocate some of the budget for spikes on the antenna to
prevent pidgeons perching on it!
Tony H
On 10/05/2014 15:15, Attila Kinali wrote:
On Fri, 09 May 2014 18:46:05 +0100
Tony tnuts@toneh.demon.co.uk wrote:
Quite a remarkable datasheet for a low cost part - I've not found any
other low cost oscillator with either of those specifications, and even
some (most?) of the OXCO don't specify the freq/temp slope.
I'm quite sure the manufacturers have this data, but they do not readily
publish it because it is not tested for and thus not guaranteed.
Ie the manufacturers want to prevent someone from taking that data,
constructing some "specs" in their mind and blaming the manufacturer
when the circuit fails because the part didn't meet the "specs".
Absolutely - which is why I was surprised to see those specs in the
datasheet (on Digikey's site). And why I wasn't surprised that I
couldn't find that version of the datasheet anywhere else including the
manufacturer's own website.
Usually the manufacturers are quite happy to share that data if you
ask nicely.
Attila Kinali
Yes , but that isn't much help unless you have a lot of of clout with
the manufacturer, like the Apples of this world, or you are able to take
on the risk that the parts will meet your needs and can buy all the the
parts you're going to need in one go. The manufacturer won't guarantee
any data that isn't in the datasheet and worse they can change the
design or manufacturing process at any time; the part would still meet
the published specs but all other characteristics could change considerably.
Tony H
On Mon, May 12, 2014 at 3:03 AM, Tony tnuts@toneh.demon.co.uk wrote:
Unfortunately they use way too much power - 800mW maximum compared to 50mW
for a UBLOX MAX-7c which are around $15. It also is specified at 50ns rms,
99% < 100ns. It appears that most, if not all, the timing type modules are
higher power as well as more expensive; unless anyone has any better
suggestions it looks like I'll have to stick to navigation type modules.
I think they use more power because a timing mode GPS is used at a fixed
location and so is likely to have AC mains power available and if a backup
battery is needed it can be a large gell cell type
--
Chris Albertson
Redondo Beach, California
On Mon, May 12, 2014 at 3:03 AM, Tony tnuts@toneh.demon.co.uk wrote:
Unfortunately they use way too much power - 800mW maximum compared to
50mW
for a UBLOX MAX-7c which are around $15. It also is specified at 50ns
rms,
99% < 100ns. It appears that most, if not all, the timing type modules
are
higher power as well as more expensive; unless anyone has any better
suggestions it looks like I'll have to stick to navigation type modules.
I think they use more power because a timing mode GPS is used at a fixed
location and so is likely to have AC mains power available and if a backup
battery is needed it can be a large gell cell type
More likely its lower power needs is because the uBlox tech is 10+ years
more recent than the old Motorola stuff.
--
Björn