[GPS_Standard] Frequency Standard Magnetic Field and Antenna Questions

[Graham / KE9H]

Harv:

Regarding the antenna...

It depends on the level of accuracy you are looking for.

An antenna in the clear, that can not see any reflected signals and has 
a clear view
of the horizon is important for maximum accuracy.

Reflections cause errors in position that translate to errors in time.

Good geometry among the satellites used in the timing solution is 
important. That is
usually something like three equally spaced around the horizontal, and 
one overhead.

On the other hand, if you are happy with about 5 or 10 milliHertz 
accuracy, (about 1 part in 10^-9)
then your current antenna setup as described will work, and is good 
enough for many purposes.

Since the GPS satellites do not fly further north than about 55 degrees, 
a North facing
window in the upper US is not optimal, because most of the satellites 
you are seeing are
going to be reflections and not the direct signal.

--- Graham / KE9H

==

Harv Weiner wrote:
> Hello,
>
> I am in the process of building the GPS-Derived Frequency Standard and have some questions:
>
> 1.  Most of the units I have seen do not have the power transformer in the same box as the OXCO and GPS. 
>         
>          Is there a concern about the magnetic field from the transformer?  What is the concern?
>
>         If so, can the transformer be shielded, by a copper shield around the core or a steel cover?  I would like to put "all the pieces" in one box
>
>
> 2.  I have the Oncore UT+ GPS receiver and am wondering about the position of the antenna.  I can capture anywhere from 2 to 6 satellites 
>     and the number varies with time.  The antenna is located in a window facing north.  Getting the antenna outside is difficult, since cable routing involves a tortuous path.
>
>         Is this enough satellites for an accurate frequency calibration?
>
>         The Oncore user manual is quite specific about antenna location and mounting. Do most users have the antenna outside? 
>
>         Is there a recommended cable to minimize losses?
>
> I am looking forward to completing this project so I can calibrate some test equipment.  Having a frequency standard with such accuracy on my work bench is an impressive addition.
>
> Thanks!!
>
> Harv
> W1BMY
>
>