[GPS_Standard] Fw: Frequency Standard Magnetic Field and Antenna Questions

[Stanley Reynolds]

----- Forwarded Message ----
From: Stanley Reynolds <stanley_reynolds at yahoo.com>
To: Harv Weiner <harvw at cox.net>
Sent: Sun, February 28, 2010 6:05:24 PM
Subject: Re: [GPS_Standard] Frequency Standard Magnetic Field and Antenna Questions

OCXO is sensitive to temperature changes and microphones, so the transformer or other metal that vibrates could be a problem. In theory one satellite is enough and zero or holdover on a good OCXO may be OK short term. That said errors due to multi-path signals and changes between satellites will introduce errors. I would mount the antenna with the best view to the south and strait up as possible. I use 75 ohm cable TV coax with good luck and it is low cost. If you have a long cable run greater than 100 feet, an antenna with a higher gain preamp maybe needed. I would think most do use outside antennas. Antennas that include the Gps receiver is another possible solution with RS-422 PPS and time signals as outputs.

Stanley


----- Original Message ----
From: Harv Weiner <harvw at cox.net>
To: gps_standard at mailman.qth.net
Sent: Sun, February 28, 2010 4:12:51 PM
Subject: [GPS_Standard] Frequency Standard Magnetic Field and Antenna Questions

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