Comtech EF Data OAC-170D User manual

OAC-170D 70 MHZ AMPLIFIER ADJUSTMENT
The OAC-170D Amplifier Adjustment is performed to ensure that the total gain from the
Downconverters to the input of the CS6716 is set for 40db +/- .25db. The OAC-170D
provides the necessary gain between the downconverter outputs and the CS6716 digital
troposcatter modem inputs via four 16db adjustable IF amplifiers.
NOTE: This procedure is not normally required in the field; however, it should be
performed after the replacement of any major equipment in the receive chain. LNA,
downconverter, IF Test Panel and/or any associated cables in the receive path.
STEP 1
Set the CS6716 modem to Default Configuration and place Modem to Online state:
a. On the modem front panel keypad, select ENT for Main Menu then select
ON/OFFLINE, then select OFFLINE to place the modem in the offline state.
b. From the Main Menu select CONFIG, then select DEFAULT to set the modem to
default configuration.
c. From the Main Menu select ON/OFFLINE, and then select ONLINE to place the
modem into the online state.
STEP 2
Remove all of the U links from the IF Data Patch Panel as shown in Fig 1.1.
Figure 1.1

STEP 3
Set the Filter select switch on the OAC-170D to BYPASS.
STEP 4
Connect the TX1 IF output to the RX1 IF input on the IF Data Patch panel using the
supplied 16db inline attenuator as shown in Fig 1.2.
Figure 1.2
STEP 5
On the modem front panel keypad, Select ENT for Menu, select MONITOR, then select
RSL to display the Receive Signal Level (RSL) for all four receive channels.
STEP 6
On the OAC-170D front panel, adjust RCVR-1 potentiometer until a reading of -40 dBm
is obtained on the CS6716 modem RSL1 display, refer to Fig 1.3
NOTE: Clockwise (CW) Increases the level.
Figure 1.3

STEP 7
Repeat steps 4-6 for each corresponding RX IF inputs 2, 3 and 4. Refer to Fig 1.4 and
Fig 1.5.
TX1IFtoRX2IF
TX1IFtoRX3
IF
TX1IFtoRX4IF
Figure 1.4
Figure 1.5
STEP 8
Restore equipment to original configuration.

GAIN EQUALIZATION
This procedure is performed to equalize the total gain through the receive path to the CS-
6716 modem. Gain Equalization is necessary for the modem to take advantage of the
multiple diversity schemes in the various AN/TRC-170 systems
STEP 1
For proper Gain Equalization, the system must not be in loop-back and the RX system
must be tuned at least 100 MHz away from the XMT frequency. If the antenna and
waveguide have not been installed, place the waveguide terminators or cover plates on
the receive ports of the waveguide entry panel. If the antenna and waveguide have been
installed, adjust the receiver amplifier converter and frequency synthesizer receive
frequency at least 200 MHz away from the normal receive frequency and at least 100
MHz from the transmit frequency. Make sure the HPA is off.
STEP 2
Set the CS6716 modem to Default Configuration and place Modem to Online state:
d. On the modem front panel keypad, select ENT for Main Menu then select
ON/OFFLINE, then select OFFLINE to place the modem in the offline state.
e. From the Main Menu select CONFIG, then select DEFAULT to set the modem to
default configuration.
f. From the Main Menu select ON/OFFLINE, and then select ONLINE to place the
modem into the online state.
STEP 3
On the modem front panel keypad, Select ENT for Menu, select MONITOR, then select
RSL to display the Receive Signal Level (RSL) for all four receive channels.
STEP 4
On each Downconverter, turn the Noise Test Switch to PRESEL as shown in fig 1.1.

Figure 1.1
STEP 5
While observing the RSL levels on the CS6716 Modem front Panel display, adjust
RCVR1-RCVR4 potentiometers on the OAC-170D for the lowest common RSL to
within +/- 0.25 dB. Refer to fig 1.2 and fig 1.3.
NOTE: The lowest RSL is the highest numerical value i.e. -74 is lower than -72.
Therefore RCVR-2 and RCVR-3 need to be adjusted from -72 down to -74 in fig 1.2.
When adjusting the potentiometers; Clockwise (CW) increases the level and Counter
Clockwise (CCW) decreases the Level.
Figure 1.2
Properly gain equalized system
Figure 1.3
STEP 6
On each Down Converter, turn the Noise Test Switch to OFF and tune the receiver
amplifier-converter and frequency synthesizer receive frequency back to the normal
receive frequency.