Bird Brain 4391A Benutzerhandbuch

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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 connectors, 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 element 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.

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 

FWD CW
RFL CW
SWR

 

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The reflected element must have a nominal power range 

one tenth that of the forward element.

FWD PEP
RFL PEP
% MOD
FWD dBm
RFL dBm
RTN Loss

 

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