Bird Technologies 4331 - Manual (Page 48)

this part be properly maintained. If the spring finger of the dc contact
requires adjustment, it may be done manually if done carefully. The button
must be positioned far enough out to maintain good contact with the element,
but not so far as to interfere with easy entry of the element body. The dc
jack, with spring finger, may be removed for access by:
1. Unscrewing the two 4-40 fillister head machine screws
which fasten it to the side of the RF line section.
2. Retract its assembly, watching carefully so as not to lose
the small Teflon positioning bead that straddles the base
of the phosphor bronze spring and nests in a counterbore
on the side of the RF body.
3. Replace the assembly (be sure that the bead is again prop-
erly inserted) and the two screws previously removed.
Calibration Checks - Thruline Wattmeter vs
Termaline Wattmeters
It is recognized that calibration of absorption wattmeters is difficult and
likely to be inaccurate unless comparison is made with a transmission,
through, type of standard. With the Thruline Wattmeter being of such type,
a natural question is: Can a Thruline Wattmeter be used to check or
recalibrate absorption wattmeters, such as the Bird Electronic Corporation
Termaline Wattmeter, when both are rated at ±5 percent of full scale
accuracy? The main question is one of exact power calibration.
The answer is a qualified yes, although with both instruments being about
equally old and known to be undamaged, there is not too much reason to
prefer either on probable accuracy. The edge is somewhat in favor of the
Thruline Wattmeter because each element covers a range of only 2-1/2 to 1
in frequency and will be flatter originally over this range than the Termaline
Wattmeter can be held initially over its very much wider, 16.7 to 1, frequency
range. Also the Thruline Wattmeter will probably exhibit smaller changes
with time, because of the narrower frequency range. It is simpler in general
design and easier in function (does not have to serve as a power load), and
it does not become heated in operation.
Bird Model 43 Wattmeter
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