Research Concepts RC2000A - Manual (Page 103)

RC2000A Dual Axis Antenna Controller Appendix I 2.6x Addendum 103
If the AGC has NEGATIVE polarity and the signal strength is too low, adjust the OFFSET pot
clockwise. If the AGC has NEGATIVE polarity and the signal strength value is too high, adjust the
OFFSET pot counter-clockwise.
9. Position the antenna 'RCVx - off satellite – weak band'. If the signal strength is between 50 and
100, proceed to step 11. If the signal strength is less than 50 or greater than 100 perform steps 8
and 9 again.
10. Position the antenna 'RCVx - on satellite – strong band'. Jog the antenna off of the satellite until the
picture is just barely watchable. Note the signal strength value. Go to CONFIG mode and use the
SCROLL keys to bring up either the AGC C Band Threshold item or the AGC K Band Threshold
item, whichever is appropriate for the frequency band that the user has chosen to operate at (and
has adjusted the pots at). Key in the signal strength value noted above. Terminate the entry with
the ENTER key.
For a dual receiver system, both AGC channels are used. The thing to remember is that the same
‘Threshold value is applied to both channels for operation at a given band.
2.2 Checking the AGC Pot Adjustments
In the previous section a procedure was presented to adjust the AGC pots and to determine the AGC
C/Ku Band Thresholds. That adjustment was performed using one transponder on one strong satellite.
After the AGC pot adjustment has been performed a check should be made to insure that the
adjustments are valid for all transponders on strong and weak satellites. In some cases, additional
potentiometer or ‘Threshold adjustments may be required.
To understand the tests that need to be performed, recall that the purpose of the AGC input is to let the
controller determine whether a satellite signal is present or not, and to provide relative signal strength
information when for peaking the antenna. A signal is assumed to be present whenever the AGC input
is above the threshold level for whichever band - C or Ku - has been selected.
Three possible problems can be encountered …
i) The receiver is tuned to an inactive transponder and the AGC input is above the appropriate
Threshold. In this case the controller will attempt to peak the antenna because the AGC input is above
Threshold. The controller will attempt to peakup the antenna but a true peak cannot be found. In the
process, the antenna may move away from the actual position of the satellite. Note that the noise
output of a satellite recevier will increase when the antenna is aligned with the sun. This will occur
when the sun lies in the earth’s equatorial plane – this occurs in mid March and mid September. Note
that if the controller is peaking the antenna on the sun, in many cases a Peak Limit Error will occur –
see chapter 3 for more information.
ii) The antenna is aligned with a satellite, the receiver is tuned to an active transponder, but the AGC
input is below the appropriate threshold. In this case peaking will not occur because the AGC is below
threshold.
iii) The antenna is aligned with a satellite, the receiver is tuned to an active transponder, but the AGC
input channel is saturated (AGC reading near 1023). In this case peaking will occur but a true peak will
not be found because moving the antenna closer to or farther away from the satellite does not change
the signal strength as displayed by the controller.
2.2.1 AGC Above Threshold for Noise Input Test
To insure that (i) is unlikely to occur tune the antenna away from any satellite. Tune the receiver over
all transponders on any frequency bands of interest. Watch the displayed signal strength to insure that
it is never above the appropriate Threshold. If the antenna is equipped with a four port feed that can
receive both C and Ku band, horizontal and vertical polarizations simultaneously (like the Seavey
ESA124D), make sure that the test is performed with both bands and both polarizations. Additionally, if
both controller AGC channels are in use, perform the test for both receivers (the Scroll Up/Down keys
can be used to select the AGC channel of interest from MANUAL mode).
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