Bird Technologies 4314C - Manual (Page 26)

14
Making Low Reflection Readings
It is sometimes desirable to make more accurate low reflection readings. This
can be done using a more sensitive element, provided that care is taken to pre-
vent application of high forward power to the low-power element. This proce-
dure is limited to use with higher power transmitters only.
1. Measure watts forward, using the proper Plug-In Element.
2. Reverse the arrow direction of the element to determine the general level of
reflected power.
3. Remove the Plug-In Element.
4. Insert a lower power element which has a maximum rating of more than
the reflected power indicated in the first measurement.
5. Insert the element, carefully, so that it reads reflected power only.
6. Read the reflected power on the meter in the usual manner.
Note: When using the two-element method of reading low
reflected power, it is not recommended to use a pair of elements
which has a full scale power differential of greater than 10 to 1.
Testing Lines, Connectors, Filters & Related Components
Lines, connectors, filters, and related components can be tested using the Thrul-
ine Wattmeter. The method of testing depends upon the circumstances involved
for any particular test. Some of these tests are listed below:
The standing wave ratio or the reflected-power to forward-power ratio of a line
can be determined by terminating the line with a good load resistor, such as a
Bird Termaline Load Resistor. Proceed as described under determining VSWR.
Low reflected power may be measured as described above.
Line attenuation (power lost as heat in the line) can be determined by inserting
the line of unknown value between two Thruline Wattmeters. The end of the line
must be terminated by a load resistor. The attenuation of the line can be deter-
mined by comparing readings made at the two ends. Allowances must be made
for normal instrument error where very small values of attenuation are involved.
Some correction may be made by direct rigid connection of the Thruline Wattme-
ters.
CAUTION
When making low reflection readings using a more sensitive element, take care
to insert the element so that it senses reflected power only. Do not rotate the
element in the socket so that it is subjected to forward power. This can result in
damage to the Plug-In Element, the wattmeter, or both.