[hpsdr] Gibralter?

[Eric Ellison]

Chris and Michael..

Thanks for your comments, hopefully anyone interested in Gibralter will get
in on this discussion. Anyone interested in a world class time/frequency
standard might get in on the discussion. The project should be flexible
enough in simple form inputting 1 pps to an FPGA or 10 mhz to an FPGA and
putting it on to the Atlas Buss OR as complex as mounting a world class GPS
timing receiver, and TCVCXO oscillator.

The current WIKI has a very good outline and suggestion for parts. I search
the GPS quite frequently, however, nothing I have found beats the iLotus
M12M Timing. I would not settle for less than that product at this point.
The two oscillators suggested are also not 'chicken feed' since they are
long lead time and about $250 per.

Although the wiki does not mention FPGA, they are INEXPENSIVE, and certainly
a 'hardware interface' between the 1 pps and 10 mhz osc, and the buss etc.
Any design really should feature an FPGA to do all sorts of conditioning,
smoothing, trend analysis, ambient temperature monitoring, corrections,
frequency division, check of the internet for NIST corrections etc. Software
Definition of the time standards thus interfaced should produce a world
class standard on the long term and very stable short term precision.

Just thoughts. The lifeblood of this forum!

For those interested, Let's see if we can Google a BETTER GPS than the
iLotus M12M Timing or the Valpy Fischer and Crystek VCXO. I have looked at
the SiRF and Trimble, but like the iLotus better, although I don't think
they offer just the 'chip'.

iLotus reference from WIKI

http://ilotus.com.sg/images/M12MT_compressed.pdf

Check the Wiki for he VCXO's suggested from VF and Crystek


Thanks
Eric - AA4SW




-----Original Message-----
From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of
michael taylor
Sent: Wednesday, June 13, 2007 1:06 AM
To: hpsdr at hpsdr.org
Subject: Re: [hpsdr] Status of THOR - Gibralter?

***** High Performance Software Defined Radio Discussion List *****

On 6/12/07, Chris Albertson <chrisalbertson90278 at yahoo.com> wrote:
>
> The problem I've seen with the low cost consumer GPS units is that
> the output is serial NMEA.  The internal clock might be very good but
...
> There are some GPSes that provide a TTL level pulse per second
> This is what yo want.  But I don't think these sell for under $100.
> (But I hope some one will correct me here.)

These are not SiRF chipsets, but they are $50-$100 and provide a PPS
(pulse per second) to align the NMEA sentence. I forget which one, but
at least one claims within +- 50ns of UTC.

<http://www.sparkfun.com/commerce/product_info.php?products_id=7951>
<http://www.sparkfun.com/commerce/product_info.php?products_id=163>
<http://www.sparkfun.com/commerce/product_info.php?products_id=8291>
<http://www.sparkfun.com/commerce/product_info.php?products_id=8266>

I believe the Trimble Resolution T (within 15 ns (one sigma)) is
between $75-100 in quantities of 1's.

> But do we care?  What really matters is how long one must integrate
> the GPS time to get the desired accuracy goal of what? 10E-11 seconds?
> The GPS signal is only used to control long term drift in the ovenized
> crystal.

Actually some look at it the other way around. The ovenized crystal
oscillator is there to reduce the "phase noise" of the GPS "clock"
output.

> of a small device and hold it very stable.  The solution used here would
> be a double oven with resistive heating.  But they had another design.
> The part was clamped to a small block of silver, a Peltier device (aka
> thermo-electric cooler) was clamped to the other side of the block and

I've never priced any, but I had the impression that Peltier devices
were fairly expensive when you're not talking surplus parts. I don't
think I've ever seen an oscillator built with a Peltier device.

-Michael, VE3TIX
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