Standard Communications TVM Series Owner's Manual page 54

CALT45 Application Notes
A minimum signal level of 38 dBmV is required at the ALTERNATE COMP IF IN
port to produce a proper level (60 dBmV) at the modulator's primary RF output.
However, 38 dBmV is well above the threshold level (30 dBmV ± 3 dB) for switching
to the alternate modulator. Therefore, during setup, the most technically sound
method to switch to the alternate modulator is to set the modulator to produce
38 dBmV at the ALTERNATE COMP IF IN port first. Then, turn off the backup
modulator. To switch to the alternate modulator, power the unit up.
The REMOTE IF SELECT switch can be used to manually switch to
ALTERNATE COMP IF IN input for manual control systems. However, the Auto
mode must be disabled by grounding the REMOTE IF SELECT.
CALT45 Installation Verification Procedure
1. Connect the IF output from another modulator to the ALTERNATE COMP IF
input.
2. Verify that the TVM450/TVM550 automatically switches to the alternate IF
when the level reaches 30 dBmV ± 3 dB.
3. Verify that the TVM450/TVM550 manually switches to the alternate IF as the
REMOTE IF SELECT is grounded, regardless of input level.
4. Verify that the TVM450/TVM550 RF output generates 60 dBmV when auto-
matically or manually switching to the alternate IF.
TVM450/S/TVM550/S/TVM550II/TVM550IIS Owner's Manual
Option Installation
Page 5-17