Bird Technologies 4391A - Manual (Page 20)

8
Connections
The Model 4391A contains a short section of rigid 50 ohm coaxial air dielectric
transmission line. To make measurements relating to the travelling waves in a
coaxial line, that line must be disconnected at some convenient point to permit
the Model 4391A air line to be inserted.
Although the Model 4391A is normally supplied with two Female N-type con-
nectors, a variety of easily interchangeable connectors are available to facilitate
connecting to the user’s system.
Once the Model 4391A is installed in the coaxial line, a Plug-in Element or a pair
of Plug-in Elements must be selected which correspond to the frequency and
power levels to be measured.
Note: The instrument is shipped with dust plugs installed in the ele-
ment sockets. Remove the dust plugs to insert elements.
In order to take full advantage of the Model 4391A’s capabilities, two elements in a
10:1 ratio of power range should be used. If only one element is used, the other socket
should be filled with a dust plug or a higher power element. Also, for greatest accuracy,
the element(s) should be chosen having the lowest possible power range that will not
result in over-ranging. Table 1 lists elements required for each mode of operation.
Table 1 Plug-In Elements Required
The higher power element is placed in the socket marked “FORWARD” and its
arrow pointed in the direction of forward power flow (toward antenna or load).
The lower power element is placed in the socket marked “REFLECTED” and is
normally pointed in the direction opposite to forward power flow. The elements
are clamped in place by the hold-down catches on the face of the line section.
These catches must be used to avoid error due to the element not contacting
the bottom or seating plate of the socket. With the element(s) in place, set the
range switches to correspond with the nominal power range of the elements.
For example, if the forward element is a 5 watt element, the switches are set at
5 and x1. For a 250 watt element they are set at 2.5 and x100. Sometimes it is
necessary to use milliwatts or kilowatts as the unit of measure. In other words, 1
watt becomes 10 x 100 milliwatts and 2500 watts becomes 2.5 x 1 kilowatts.
Mode Forward Reflected
FWD CW 3
RFL CW 3
SWR 3 3 *
*. The reflected element must have a nominal power
range one tenth that of the forward element.
FWD PEP 3
RFL PEP 3
% MOD 3
FWD dBm 3
RFL dBm 3
RTN Loss 3 3 *