Service Manual

TSM 20-399 Rev 0, Feb 2014 25 10W VHF Amplifier
5.3.3 Forward Power Calibration
Set the exciter RF output for the transmitter to run at its operating power. Adjust R32 for a forward power meter
reading of 100%.
NOTE: Before proceeding to the next step, ensure that the Pin Attenuator Board has been setup according to the
procedure on the Pin Attenuator Board section of this manual.
5.3.4 Reflected Power Calibration
1. Temporarily defeat the VSWR cutback protection (if it has been initially setup) by adjusting R36 fully clockwise
(CW). With the transmitter still at "full power”, disconnect the RF input cable from J1 and connect it instead to the
reflected power input J2. Switch to position „RFL‟ and adjust R30 so that the reflected power reads 100. This now
corresponds to a reflected power of 100%.
2. Enable the VSWR cutback by turning R36 counter clockwise until the meter indicates 10% output. This means that
in severe VSWR conditions such as in an open circuit, the amplifier will automatically cut back to 10% in order to
protect itself.
3. Replace the cables in their proper connections. RFL meter reading should be zero and the FWD meter reading
should be back to 100%. If the FWD reading is much less than 100%, R36 was probably over adjusted.