Research Concepts RC1500 - Manual (Page 23)

AGC Tuning
23 RC1500B Quick Start Guide
AGC Tuning
Before continuing on, read through the Idirect Interface guide of this document.
The information on that page will help clarify this AGC tuning procedure.
To implement the tracking algorithms, the controller requires an input signal
which indicates the strength of the received signal. Such a signal is generated
within a satellite receiver, and is referred to as an AGC signal. (AGC is the
abbreviation for Automatic Gain Control.) On satellite receivers, this signal may
also be referred to as a ‘Signal Strength’ or ‘Tuning Meter’ output. An AGC
output typically varies in proportion to the received power of the transponder
which the receiver is currently tuned to.
1. Once the antenna is aligned with the satellite, place a voltmeter on the
receiver’s AGC output. Measure and record the voltage. In the description
that follows, the term ‘on satellite’ will be used to refer to the antenna aligned
with a strong satellite.
2. Jog the antenna off of the satellite so the antenna is looking at nothing.
Measure and record the receiver’s AGC voltage. In the description that
follows, the term ‘off satellite’ will be used to refer to this case where the
antenna is positioned well off of any satellite, looking at nothing.
3. Connect the receiver’s AGC output to the controller’s AGC2 input. Be sure to
connect the ground return of the controller to a ground on the receiver.
4. If the AGC voltage associated with the ‘on satellite’ case is greater than that
of the ‘off satellite’ case, the receiver has POSITIVE AGC polarity (otherwise
the receiver has NEGATIVE AGC polarity). Go to CONFIG mode and use the
SCROLL keys to bring up the AGC Polarity Flag item. Key in the proper
polarity using either the 0 or 1 key, and terminate the entry with the ENTER
key.
5a. If the receiver’s AGC has NEGATIVE polarity, go to step 5b. If the receiver’s
AGC has POSITIVE polarity, go to LIMIT mode and examine the signal
strength for the AGC channel which was not selected in step 3. If the signal
strength reading for that channel is greater than 10, adjust the OFFSET and
GAIN for that channel until the signal strength reading for that channel is less
than 10. To lower the displayed signal strength turn the OFFSET pot
clockwise and the SCALE pot counter-clockwise. Be sure not to turn the
controller off while the controller is in LIMITS mode, or else the limits which
have previously been set will be corrupted. Proceed to step 6.
5b. If the receiver’s AGC has NEGATIVE polarity, connect a jumper from the
controller’s unused AGC input channel to connector J1, pin 11. Go to LIMIT