88950-A Series


98950-A Series


INSTRUCTION MANUAL Specifications And Leading Particulars

The 88950 and 98950 series Wattmeter is designed to work with
any Coaxial Dynamics line section and the appropriate elements to
accurately indicate the power in coaxial transmission lines. They
are used to indicate power from 100mW to 100kW.
They are all equipped with an easily read 4 ½ mirror backed triple
scale meter.

88950 Series

Models With 5/10/25 Scales
Model 88952-A
High power 30uA meter in case for use with external single socket
line sections.
Model 88954-A
High power 30uA meter in case with a FWD/RFL switch for use
with external dual socket line sections.

Models with 15/30/60 Scales
Model 88958-A
High power 30uA meter in case for use with external single socket
line sections.
Model 88959-A
High power 30uA meter in case with a FWD/RFL switch for use
with external dual socket line sections.

Specifications And Leading Particulars (cont.)

98950 Series

Models With 5/10/25 Scales
Model 98952-A
High power 30uA meter in case for use with external single socket
line sections.
Model 98954-A
High power 30uA meter in case with a FWD/RFL switch for use
with external dual socket line sections.

Models with 15/30/60 Scales
Model 98958-A
High power 30uA meter in case for use with external single socket
line sections.
Model 98959-A
High power 30uA meter in case with a FWD/RFL switch for use
with external dual socket line sections.






General Description

1. Purpose and Application

The 88950 series of Wattmeters are designed to measure power
flow and match, when used with the appropriate line sections and
elements. They are designed for use with CW, FM, AM, and
analog TV systems. They are not for use with digital or pulsed
applications. They normally are supplied with a 10 cable, but can
be supplied with cables up to 200 without any loss of accuracy.

The 98950 series of Wattmeters are designed to measure power
flow and match, when used with the appropriate line sections and
elements. They are designed for use with complex waveforms such
as CDMA, DAB, DTV, IBOC as well as CW, FM, AM, and
analog TV systems. They normally are supplied with 10 cables,
but can be supplied with cables up to 200 without any loss of
accuracy.


2. Description

The 88950 series of Wattmeters includes a case with carrying
strap, a shock-mounted mirror backed triple scale meter and
cable(s) to attach to the line section. The case has four rubber feet
on the base.

The 98950 series of Wattmeters includes a case with carrying
strap, a shock-mounted mirror backed triple scale meter and cables
to attach to the line section and the element and a plug in wall
power supply. The case has four rubber feet on the base. On the
rear cover are SMA connectors used to supply DC power to the
element via a length of shielded cable equipped with SMA
connectors.
General Description (cont.)

3. Theory of Operation

The operation of the 88950/98950 series Wattmeters is based on
the traveling wave concept of RF transmission. As RF is applied to
a transmission line, there is a forward wave traveling from the
transmitter to the load, and a reflected wave traveling from the load
to the transmitter. The closer the load is matched to the
transmission line the smaller the reflected wave will be. To
determine the RF power dissipated in the load, it is necessary to
determine the RF power of the forward wave and the RF power of
the reflected wave. The difference between the two will be the
power absorbed by the load.

The interference between the forward and reflected waves
produces a standing wave in the system. In the standing wave
concept, VSWR (voltage standing wave ratio) is a widely used
tool. There is a simple relation between forward power, reflected
power and VSWR.


Let
W
f
represent forward power.



W
r
represent reflected power.

Then







W
r
1+
W
f



VSWR=
1-

W
r

W
f


General Description (cont.)

For example: 1% reflected power is about 1.2:1 VSWR and 10% is
about 2.0:1 VSWR.

It can be seen that the VSWR is an index of the magnitude of the
mismatch between the source and the load.

The charts supplied can convert W
f
and W
r
to VSWR.

When the line section and element are inserted in the transmission
line the element is both capacitively and inductively coupled to the
main line. Voltages proportional to the RF voltage and current in
the main line are induced in the element circuitry. The coupling is
so adjusted that the induced voltages add in the sensitive direction
and cancel in the opposite direction. These voltages are rectified
and the resulting DC current is applied to the meter, which is
calibrated to represent the power in the main transmission line.

In the 98950 series the RF voltages from the element are fed to
some additional circuitry to provide the correct measurements of
the complex waveforms.



Operation

1. General Procedure

To make readings with the Wattmeter, it is necessary to select and
install a plug-in detector element of the proper power and
frequency range, connect the cables to the line section in the
transmission line and read the meter with the element in the
forward and reverse direction. Subtraction of the reflected power
from the forward power provides the power dissipated in the load.
To determine VSWR, first determine the forward and reflected
power and either use the formula or the charts provided.
Maintenance

Maintenance of the 88950/98950 series of Wattmeters normally is
limited to cleaning. The amount of cleaning necessary will depend
on the environment the Wattmeter is operated in. Keeping an
element in the socket of the line section will provide an effective
seal against dust and dirt. When necessary, clean the element seat
in the line section with a cotton swab. Pay particular attention to
the bottom rim of the element seat and the body of the element. If
necessary, the spring finger of the DC contact may be adjusted to
make contact with the contact on the element.

CAUTION: When making adjustments in the line section use
extreme caution. The high RF voltages present in the line
section can cause serious injury or death.

Replacement Parts

Common Parts to 88950/98950 series:
Meter 5/10/25 scale
88950-A
Meter 15/30/60 scale
88959-A
Cable with DC connector:
10
88901
25
88902

50
88903
100


88904
200


88905

For 98950 series only:
DC cable with SMA connectors:


25
88927

50
88928
100


88929
200


88930

Wall Plug-in Power supply
120 VAC/60 HZ

9725
230 VAC/50 HZ

9726
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