Research Concepts RC2000A - Manual (Page 104)

104 RC2000A Dual Axis Antenna Controller Appendix I 2.6x Addendum
2.2.2 AGC Input Below Threshold for Active Satellite Transponder Test
Perform the following procedure to insure that type (ii) problems do not occur.
Align the antenna with a weak satellite.
Tune the receiver over all transponders on any frequency bands of interest.
Insure that for all active transponders the displayed signal strength is above Threshold.
Note that for four port feeds, perform the test for both bands and both polarizations. For installations
that utilize both controller AGC input channels, perform the test on both receivers. From MANUAL
mode, the Scroll Up/Down keys can be used to select the AGC input which is displayed. As an
alternative to aligning the antenna with a weak satellite, a strong satellite can be employed if the
antenna is jogged off of the satellite to reduce the received signal strength.
2.2.3 AGC Input Saturated for Active Satellite Transponder Test
Perform the following procedure to insure that type (iii) problems do not occur.
Align the antenna with a strong satellite.
Tune the receiver over all transponders on any frequency bands of interest.
Insure that for all active transponders the displayed signal strength is well below saturation. A
conservative approach is to treat any signal with a displayed signal strength above 900 as saturation.
Note that for four port feeds, perform the test for both bands and both polarizations. For installations
that utilize both controller AGC input channels, perform the test on both receivers. From MANUAL
mode, the Scroll Up/Down keys can be used to select the AGC input which is displayed.
2.2.4 What to do if Problems are Found
For a type (iii) problem in the absence of type (i) or type (ii) problems. the pot adjustment procedure can
be performed again using the transponder/satellite where saturation was encountered as the ‘on
satellite’ signal.
For type (i) or type (ii) problems, it may be possible to adjust the Threshold values up or down. For a
given AGC input (receiver), if type (i) problems are encountered for one band and type (ii) problems are
encountered for the other band, the insertion of pads (attenuators) or amplifiers in the IF line can
sometimes help.
If problems persist the usual culprit is gain flatness. An amplifier's gain vs. frequency characteristic, or
gain flatness, is the variation of the amplifier's gain with changing frequency. The ideal response is to
have a flat gain characteristic (the gain does not vary with frequency).
There are four places in a satellite receiving system that may have gain flatness problems that can
affect the peakup operation. These are the LNB, the coaxial cable connecting the LNB to the receiver,
line amps (or bullet amps) inserted in the 950 - 1750 MHz IF, and the receiver's IF or AGC stages. If a
spectrum analyzer is connected into the receiver's block IF line, the gain flatness of the LNB and any
line amps present can be observed. When the antenna is pointed away from any satellite, the spectrum
analyzer displays the received noise, which should be constant with frequency. If the display is not
horizontal then some gain variation with frequency is present. The type (i) test above is essentially a
test of gain flatness.
Most gain flatness problems can be traced to a problem with the coaxial cable connecting the antenna
to the receiver (sometimes called a 'suck-out') or to bullet amplifiers. Some bullet amplifiers have been
observed to have really terrible gain flatness characteristics.
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