RESEARCH CONCEPTS RC2000C Manual page 40

32 RC2000C Az/El Tracking Antenna Controller
3. Similar to step 3 above. The only modification is that the user should select the frequency band
whose 'on satellite' and 'off satellite' receiver AGC voltage difference is the greatest to make the
determination of which AGC channel to use.
4-5. No changes from steps 4 and 5 which are outlined above.
6. As outlined above, in the next few steps the user will adjust the GAIN and OFFSET pots of the AGC
channel that is connected to the receiver. The difference is that in steps 7 through 9 the term 'on
satellite' must be replaced with 'on satellite, strong band' and the term 'off satellite' must be replaced
with 'off satellite, weak band'. These terms are described below.
The term 'on satellite, strong band' refers to the case when the antenna is aligned with a satellite of
the frequency band that has the greatest gain. For a POSITIVE AGC polarity receiver this is the
band for which the greatest voltage was recorded in step 1. For a NEGATIVE AGC polarity
receiver, this is the band for which the lowest voltage was recorded in step 1.
The term 'off satellite, weak band' refers to the case when the antenna is positioned off of any
satellite and the receiver is tuned to the frequency band which has the lowest gain. For a
POSITIVE AGC polarity receiver this is the frequency band for which the lowest voltage was
recorded in step 2 above. For a NEGATIVE AGC polarity receiver this corresponds to the
frequency band for which the greatest voltage was recorded in step 2 above.
7. Similar to the step 7 outlined above. In place of 'off satellite' use the term 'off satellite, weak band'
as described above.
8. Similar to the step 8 outlined above. In place of 'on satellite' use the term 'on satellite, strong band'
as described above.
9. Similar to the step 9 outlined above. In place of 'off satellite' use the term 'off satellite, weak band'
as described above.
10. Similar to the step 10 outlined above except that jogging the antenna 'on satellite' and then slightly
off should be performed for each frequency band to obtain both the AGC C Band Threshold and the
AGC K/L Band Threshold. Both of the threshold values should be entered into the controller via
CONFIG mode as outlined above.
Using Two AGC Channels
Connecting a second receiver to the controller is straightforward. The controller AGC input channel
GAIN and OFFSET adjustments have enough range to handle any possible receiver AGC scheme, as
long as the AGC level is less than six volts. In step 3 of the adjustment procedure, the installer is
instructed to select the controller AGC input channel based on the range of the receiver's AGC output.
AGC input channel 1 is designed to handle 'small' AGC signal swings, and AGC input channel 2 is
designed for 'large' AGC signal swings. There is enough adjustment range, however, so that either
channel may be connected to any receiver AGC output.
If two receivers are used, both must have the same AGC polarity, and the GAIN and OFFSET pots of
each channel must be adjusted so that the same threshold values are appropriate for each channel.
The controller will use as its AGC input the stronger of the two signals. All pot adjustments will have to
take place in LIMITS mode, because this is the only mode where the voltages that correspond to each
AGC channel may be viewed simultaneously and unambiguously.
Amplifier Gain vs. Frequency Characteristics
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). Amplifiers with poor gain flatness characteristics can cause problems for the tracker.
This section describes a simple test (no equipment required) that the user can carry out to check the
receiving system's gain flatness.
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