[time-nuts] Checking the Frequency of a Rubidium Oscillator

Brooke Clarke brooke at pacific.net
Tue Nov 11 19:12:21 UTC 2008


Hi Bruce:

It's my understanding that if you look at the signal from a common GPS antenna 
and feed it into a spectrum analyzer you will not see the signal.  My guess is 
that when developed by the military it was designed to be a stealth system. 
GPS is what's called a Spread spectrum signal.

Also the best possible s/n radio is determined by how orthogonal the different 
PN codes are to each other.  These are described in ICD-GPS-200 which is on 
line at:
http://www.navcen.uscg.gov/gps/geninfo/
along with other GPS info.

Here's a National Instruments page about GPS signal generation:
http://zone.ni.com/devzone/cda/tut/p/id/8015
The definitions on this page for the various Time To First Fix flavors may not 
be accurate.

Have Fun,

Brooke Clarke
http://www.prc68.com

Brucekareen at aol.com wrote:
>  
> I  have an EIP Model 548 counter with a YIG-tuned front end that can be 
> programmed  to scan over narrow frequency ranges.  By feeding the rubidium 
> oscillator under test into the 10 MHz clock input  of the counter, is there any 
> reasonably simple way to directly measure the  frequency of a GPS satellite 
> transmission so as to ascertain the accuracy of the  rubidium source?  The counter has 
> an  input sensitivity in the order of about –25 dBm -- not sufficient to 
> measure  directly from an amplified antenna, but perhaps through an amplifier.  I 
> am not sure whether the input YIG  tuner selectivity is sufficient to separate 
> transmissions from the various  satellite’s (or are they TDMS?).  What do you 
> think?   
> Bruce,  KG6OJI
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