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criteria for deep space operations in the 2 GHz band. This recommendation indicates
that the protection criterion for deep space Earth stations operating near 2 GHz is that
the interference at the input to the deep space earth station receiver should not exceed
-222 dBW/Hz and current NASA policy is that this criterion must be met 100% of the
time. This protection criterion is measured at the deep space Earth station after
accounting for the receiving antenna gain. Platforms operating in the upper portion of
the 2200 – 2290 MHz band need very stringent filtering to meet the deep space
protection criteria. In particular, a platform using the 2287.5 MHz TDRSS return links
with a necessary bandwidth of 5 MHz or higher will easily violate the deep space
protection criteria when it transmits sufficiently close to the beam of a DSN 70 meter or
34 meter antenna.
Mitigation techniques such as filtering out sideband emissions have been very
successful to meet the deep space protection criterion. In particular, the “NASA/GSFC
Recommended Filtering Referenced to the Output of the Power Amplifier (see Figure D-
6)” minimizes the interference in the DSN band with a reasonable implementation loss.
Figure D-7 shows an example of the spectral output of an unfiltered BPSK signal vs. a
signal filtered by the “NASA/GSFC Recommended Filtering Referenced to the Output of
the Power Amplifier” and compares them to the DSN protection criterion. The use of
filtering with performance consistent or better than the “NASA/GSFC Recommended
Filtering Referenced to the Output of the Power Amplifier” is strongly encouraged due to
the considerable benefits that this provides. For example:
The DSN coordination angle, which is defined as the angle off of the DSN main
beam gain where the SN 2287.5 MHz customer meets the DSN protection
criterion, is reduced by a factor of three and six in the 1 st and 2 nd sidelobes,
respectively, for a mission with this filter as compared to a mission without this
filter.
This reduction in coordination angle results in filtered missions exceeding this
coordination angle approximately one-tenth of the time that a mission without a
filter exceeds the coordination angle.
Revision 10 D-17 450-SNUG