[time-nuts] Measurement of Rubidiums

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jun 9 20:05:59 EDT 2008

Jim Robbins wrote:
> Hi all,
>     Well, I have good news and bad news.
>     The good news is that I believe I now know why I was getting the strange readings on my Racal 1992 with the Thunderbolt GPS and/or the Starloc II and my Rubidiums.  Neither GPS receiver was able to lock onto enough satellites (if any).  The bad news is that that the failure to lock is due to the location of my home/antenna out in the woods with the HP GPS antenna up about 10 feet above the roof (i.e. 32 feet above ground).  I am surrounded by trees in a sort of "race track" shaped clearing, with the short axis closest woods being about 57 feet from the antenna (both East and West sides) and having a height above the antenna height of 38 to 48 feet.  The long axis woods is some 75 to 108 feet from the antenna and having a height above the antenna height of between 18 feet (South) and 48 feet (North)!  The long and the short of it is that the angle of view of the satellites is seriously blocked and varies from 35 degrees to about 7 degrees in the South!
>     Sorry that my contribution to the group is to reveal that you probably can't use GPS if you live in a hole in the woods!  I've played with the geometry and I'd need a very tall tower to get the angles all down to 7 degrees or less.  I am discourged, to say the least.  Anyone got any other ideas besides going back to Loran?
> Jim Robbins 

A modern GPS timing receiver only needs one satellite in view when in 
position hold mode.
The self survey hower requires more satellites in view.

If you can determine your latitude and longitude accurately by other 
means and set the GPS location to this position you may be able to use 
the system in your hole in the woods.

To get a better idea you need to check the frequency at which at least 
one satellite is visible from your position.


More information about the time-nuts mailing list