Service manual

RC2000 Service Manual Chapter 4 Common RC2000 Questions 29
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4.7 DH Gibralter Mounts
The DH antenna uses a chain drive for the azimuth axis. There is not much resolution on that axis (800
counts per radian for azimuth versus 2600 counts per radian for elevation). The DH antenna is equipped
with a chain tension adjustment on one end of the chain. This adjustment is a threaded rod which tightens
up the chain. To tighten the chain position the antenna so that the azimuth drive sprocket is opposite the
chain tension adjustment and then tighten up the nut on the threaded rod.
There will always be some looseness in the chain. If the controller calculates that the step track azimuth
step size is 1.49 counts the controller will move the antenna 1 count in azimuth - there are no fractional
counts. If the slop in the antenna is 2 counts then moving the antenna 1 count in azimuth "may not
change the actual pointing angle of the antenna". This is the most common cause of PEAK LIMIT
ERRORS. The solution is to increase the MAX TRACK ERROR which will result in larger step sizes.
4.8 AGC Input Notes
It has been found that the AGC (Automatic Gain Control) output of the Drake ESR 1250 Receiver requires
a 50K to 100K pull down resistor to work properly with the RC2000 AGC input circuits. On the back of the
receiver, the resistor can be connected between the TM (tuning meter) and GND (ground) terminals.
Other Drake models may also require this fix.
4.8.1 AGC Input Voltage Range
The AGC input voltage range of the RC2000 is 0 to 6 volts. An input voltage above this range will result in
saturation of the output of the AGC signal processing circuit. It is possible to extend the range of the input
voltage by placing a resistor in series with the input.
Here is a schematic of the input of the AGC processing circuit ...
2.4 Meg |\
| \
input -------/\/\/\/\----+--------|+ \
| | +--+----- ....
| +---|- / |
\ | | / |
1 Meg / | |/ | op amp
\ | |
/ +----------+
|
|
__|__
---
Figure X