Pep Circuits; Power Supply - Heathkit HM-2140 Manual

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When switch SW4 is in the FWD (out) position, the FWD meter is again
enabled to indicate forward power, while SW3, in the SWR position, indi-
cates the amount of standing wave apparent at the point the Wattmeter is
inserted in the transmission line. When SW3 is atthe REF (out) position, the
power reflected through the transmission line from the antenna, dummy
load, etc., is indicated on the REF meter in watts.
When switch SW4 is in the FWDposition, the signals coupled from SW1 are
routed to PEP-AVG switch SW2. If SW2 is set to the AVG (out) position,
signals are direct-coupled to the FWD and REF meters. When SW2 is set to
the PEP (in) position, the incoming signals are then routed to the meters
through the PEP circuits, consisting mainly of four-section integrated cir-
cuit U1 with its associated components.
The PEP circuits consist of two sections. The first is a peak detector with
gain, and the second is a unity-gain buffer network with an offset adjust-
ment.
The forward signal is coupled from switch SW1, through SW4 in the FWD
position, through resistor R23 and the contacts of SW2 in the PEP position,
and then into the PEP circuit. Resistors R9 and R4 form a 6 dB voltage
divider while they maintain the equivalent resistance of meter M2 on the
remote sensor. This preserves the calibration of the sensor. Amplifier IC
U1C acts as a peak detector when combined with diode D2. There is a
minimum voltage gain of 1.5 which is adjustable. This adjustment allows
the gain to be varied so it will duplicate the voltage normally present at
meter M1 in the AVGmode across capacitor C6 (with some small offset due
to the effect from the operational amplifier).
The following stage is a unity-gain buffer into which an offset voltage has
been summed from resistor R17. This permits any small voltages induced
by the amplifiers to be balanced out. The result is an exact replica of the
voltage from the remote sensor to appear at U1D pin 14, with one exception.
The peak detector will catch and hold the peaks. Hence, on a CW signal the
PEP reading is the same, but on vocal tones, there will be a great difference
in readings. The time constant for the peak reading is a product of capacitor
C6 and resistors R11 and R5. If a longer or shorter time constant is desired,
the value of capacitor C6 may be changed. Use a good quality, low-leakage
capacitor.
The output from the PEP circuit at IC U1D is routed to the FWD meter
through switch SW2 and contacts 1, 2, and 3 of switch SW5.
The power for the Wattmeter is taken directly from either a 9-volt NEDA
Type 1604 battery or from the Heathkit Converter Model GRA-43-1. When
only the 9-volt battery is connected to the switch circuit board, the closed
contacts of accessory jack J1 connect the positive and negative battery
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