Heathkit HM 102 Manual 2

Page 1

Assembly
and
Operation
of the

HEATHKIT

RF POWER METER
MODEL HM-102

TABLE OF comems I
Introduction .................... 2
Parts List ...................... L 2
Step-by-Step Assembly ............... 4

Circuit Board Assambly ............ 4
Remote Chassis Assembly ........... 7
Cabinet Assemhly ............... I T0
Cabinet Wiring .............. . . 12
!
Calibration ..................... '3
Operation ..................... '5
In Case of Difficulty ............... 18
Troubleshooting Chart ............. 19
Specifications ................... 21
Circuit Description ................. 22
Circuit Board X-Rav View .............. 22
Remote Chassis Photo ................ 23
Cabinet Photo ................... 23
Schematic. . .IfoId-out from Page] .......... 23
Replacement Parts Price List ............. 24
Warranty , . . . . . . . . r . . V Inside tron: cover
Customer Service . . r , . . . . . Inside rear cover

HEATH COMPANY
BENTON HARBOR. MICHIGAN 49022

Dog-min mm
Hum Comm
Aflmmm

Page 2

Page 22

fl HEATH [{IT'

CIRCUIT DESCRIPTION

Fiefer to the Schematic [fold-out from Page 23] while
reading this "Circuit Dewiption."

SWR BRIDGE CIRCUIT

Toroid coil [.1 is a current pickup element for forward and
reflected power. A bus wire is routed from the Input ieck
through mroid coil L1, and then to the Output iack. A
transmitted signal routed along this wire induces a current in
coil L1. The voltage formed in coil Ll is rectified by diode
03 and demupled by capacitor (:5 and resistor R4. Resistor
R3 croatesa load for forward power readings. Reverse power
readings are determined, in the same manner, by the circuit
consisting of diode D2, capacitor C2, and resistor R1.

Forward and reverse voltages are connected to the meter
thrOugh switch S2, Sensitivity control R11, and Function
switch S3.

Resistor R7 is a ground-return path for diodes D2 and DS.
Capacitors C4, 012. 013, and Cl form a voltage divider
circuit to balance the capacitive effects of the bifiiar
(deubledi windings in coil L1, which provides correct SWR
readings.

POWER METER CIRCUIT

Current is induced in toroid coil L1 in the same manner as
for the SWR bridge circuit. Resistor R2 forms a load across
coil L1 to reduce the 0 of the coil circuit. This prevents the
transmitted treQuency from affecting the wattmeter.

The wattmcter is calibrated by measuring the voltage at
control RS, which varies the power going to the meter.
Resistors R8 and R9 are voltage dividers for the two power
ranges: 200 watts and 2000 watts.

Capacitors C7 and C8, diode DI, and voltage divider resistor
R5 thrOugh switch Si complete a voltmeter circuit for the
wattmener.

By using an accurate device, wch as an RF probe with a
VTVM or a wattmeter calibrator, this Power Meter can be
caiibrated to a desired degree of aDcuraCy.

Ferrite beads L2 through L6 prevent RF from traveling
through the 5-conductor cable into the readOut circuits.

CIRCUIT BOARD X-RAY VIEW