User Manual

1. RF Metering Board 20B1235G7: Figures 1 and 2. (continued).
The output of U1-7 (U2-7) drives the RF power meter through R32 (R30) which set
the meter deflection with a known RF signal. U1-7 (U2-7) drives. Forward
calibration is done with full rated power and a forward RF sample from the
directional coupler applied to J1. R32 is adjusted for a 100% reading on the
forward power meter position.
For Reflected calibration, the same forward RF sample is then applied to J2, R30
is set for a 100% reading on the Reflected Power meter.
2. RF Metering Board Test and Calibration:
(Refer also to the Pin Attenuator section of this manual)
a) Forward Power Meter Calibration - Zero Adjust
With no RF input connected, measure the DC voltage at U1-7 (or TP1) and adjust
R18 until the output voltage at U1-7 (TP1) drops to a minimum, approximately 10
to 50 mVDC. A DC coupled scope will make the adjustment easier to see; the
objective is to place the U1 output as near the op-amp ground rail as possible
without the op-amp going into saturation. Turning the pot farther will decrease
the sensitivity of the system for small signals. Once this minimum voltage has
been reached, do not re-adjust R18.
b) Reflected Power Meter Calibration - Zero Adjust
With no RF input connected, measure the DC voltage at U2-7 (or TP2) and adjust
R20 for a minimum, which should be approximately 50 mVDC. Once this minimum
voltage has been reached, do not re-adjust R20. This adjustment is done in
precisely the same way as in step a) above.
c) 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 (see page 34a-1).
d) Reflected Power calibration
1. Temporarily defeat the VSWR cutback protection (if it's been initially setup)
by adjusting R36 fully clocwise (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