Spectracom Corporation
8194B, 8195B, 8197B
GPS Ageless Master Oscillator Instruction Manual
A-1
A.
Appendix A – Operation with Low GPS Quality
A.1
Introduction
The Spectracom Master Oscillator is often used to provide a reference to transmitters
when precise frequency control is needed. In some installations, the GPS reception has
been poor or intermittent, preventing reliable operation of the disciplined oscillator.
One reason for poor reception is harmonics from a local broadcast interfering with the
GPS L1 carrier of 1575.42 MHz. Certain television or FM radiobroadcasts, while
operating within their frequency allocation, can cause GPS jamming due to harmonics
of the carrier. Television interference presents a greater challenge due to higher output
power, typically 2-3 MW. Table A-1 lists the potential problem television stations and
their respective GPS harmonic.
CHANNEL HARMONIC
66 2
nd
23 3
rd
10 8
th
7 9
th
6 18
th
& 19
th
5 20
th
Table A-1
Television Stations with GPS Jamming Potential
FM radio stations, while lower in radiated power, may cause GPS jamming also. Table
A-2 lists the potential problem radio frequencies and their respective GPS harmonic.
FREQUENCY HARMONIC
104.8 - 105.2
15
th
98.3 - 98.7
16
th
92.5 - 92.9
17
th
87.3 - 87.7
18
th
Table A-2 FM Radio Frequencies with GPS Jamming Potential
