PURPOSE AND APPLICATION
The Model 43 THRULINE Wattmeter is an insertion type RF
wattmeter, designed to measure power flow and load match in
50-ohm coaxial transmission lines. It is intended for use on
CW, AM, FM, and TV modulation envelopes, but not pulsed
modes. The Model 43, when used in 50-ohm applications, has
an insertion VSWR of less than 1.05:1 up to a frequency of
1000 MHz. The meter is direct reading in watts, expanded
down scale for easy reading, and is graduated 25, 50, and
100 watts full scale. The power ranges used are determined
by the
Plug-In Elements, which fall in ten frequency band
groups covering from 2 to 2300 MHz plus additional special
Elements in various power and frequency ranges (see Section
4). Further characteristics may be found in the Summary
Sheet on page A.
2. DESCRIPTION
The Model 43 THRULINE, Figure 1-1, is a portable unit
contained in a die cast aluminium housing, with a formed
metal enclosure on the back which is easily removed.
Included with the unit is a leather carrying strap, four
rubber shock feet on the base, and four rubber bumpers on
the back, which allow the Model 43 to stand or lie flat when
used. For additional protection, the microammeter is
specially shock mounted. A slotted screw is provided on the
lower front face of the meter for zeroing the pointer. Below
the meter, the RF line section face protrudes slightly from
the wattmeter housing with the
Plug-In Element socket in the
center.
A shielded cable connects the microammeter to the dc jack
which is attached to the side of the RF line section
casting. This cable, nearly three feet long, permits removal
of the RF line section from the Wattmeter housing. Meter
connections may be maintained with any installations outside
of the housing. This permits permanent additional
installations to be made. See Section 3, INSTALLATION.
Inside the dc jack assembly, there is a
Filter capacitor
which shunts the meter circuit to prevent misreadings caused
by stray RF energy existing in the
Plug-In Element. Mounted
on the dc jack is a phosphor bronze spring finger, which
protrudes through a lateral hole and into the Plug-In
Element socket of the RF line section. The finger has a
button on its end which mates with the contacts of the
Plug-In Element. The nickel plated brass RF line section is
precision made to provide the best possible impedance match
to the coaxial RF transmission line in which the Model 43 is
Inserted. The ends of the line section are nested in mating
slots to provide additional mechanical support.
At each end of the line section are Bird Quick-Change type
RF connectors, which may be quickly interchanged with any
other Bird "QC" connector by removing the four screws on the
mounting flanges. The Wattmeter housing does not interfere
with any connector changes.
To make measurements, the cylindrical shaped
Plug-In Element
is inserted into the line section socket and rotated against
one stop. A small catch in the upper right hand corner of
the casting face presses on the shoulder of the Plug-In
Element to keep it In proper alignment and assure a good
contact with the dc jack and between the lower edge of the
Element and line section body. On diametrically opposite
sides of the
Plug-In Element body are contacts to provide dc
pick-up in either direction. These contacts make connection
with the spring finger of the dc jack only when the Plug-In
Element is in the precise forward or reverse position, and
with the index pin on the Element on the lower level of the
line section castingface against its respective stop.
Comments