BIRD THRULINE 4450, Operating Instructions & Parts List Manual

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Chap ter 4
Op er ating In struc tions
The ap par ent fea tures of the Thruline equip ment have been dis cussed in the pre ced ing sec tions. As
pre vi ously men tioned, no bat ter ies or ex ter nal power source is re quired to op er ate the wattmeter.
A suf fi cient amount of power is taken from the RF trans mis sion line to op er ate the unit. This
power is neg li gi ble and does not af fect the power out put to a no tice able de gree.
Preliminary Set-up
Be fore ap ply ing any RF power, make sure the me ter pointer is ex actly set on the ZERO mark of
the scale. If ad just ment is re quired, the pointer must be set on the ZERO mark un der no-power
con di tions with the range switch set on one of the lower power ranges. Using a small screw driver,
turn the zero ad just screw on the be zel of the me ter clock wise or coun ter clock wise as nec es sary
un til the pointer ex actly aligns with the ZERO mark on the me ter scale.
The range switch should be in the OFF po si tion or at least on the 100 watt range, when power is
ap plied. This is es pe cially true when the amount of power be ing ap plied is un known. Af ter RF
power is ap plied, the range switch may be turned to a po si tion where a power in di ca tion is given
in the up per one-third of the scale.
The mode switch should nor mally be in the FWD po si tion and switched to the RFL po si tion af ter
a for ward read ing has been taken. In the RFL po si tion a more ac cu rate re flected power read ing can
be ob tained by turn ing the range switch to a lower set ting. How ever, with this con di tion care must
be taken not to turn the mode switch back the the FWD po si tion un til the range switch has been re -
turned to its orig i nal set ting. Fail ure to do this will cause overranging of the me ter and pos si ble
dam age. This prac tice, of course, is not pos si ble when power less than five watts is be ing mea -
sured.
Reverse Power
Operation
The Model 4450 may be in stalled back ward in the trans mis sion line if nec es sary, i.e. trans mit ter
out put to wattmeter out put and wattmeter in put to load; how ever, the for ward and re flected power
in di ca tions will be re versed. There fore when the mode switch is in the FWD po si tion, re verse
power will be in di cated and the RFL po si tion will in di cate for ward power. Since the line cou plers
and cir cuitry are sim i lar, ac cept able power in di ca tions are given with lit tle, if any, change in ac cu -
racy. Re versing the unit in the trans mis sion line should only be done when ab so lutely nec es sary
since there is the po ten tial dan ger of overranging the me ter move ment.
Load Power
Where an ap pre cia ble amount of power is re flected from a load, as with some an ten nas, it is nec es -
sary to sub tract the re flected power read ing from the for ward power to ob tain ac tual load power.
RF power de liv ered to and dis si pated in a load is given by the for mula:
WL = watts into load = Wf - Wr
This cor rec tion is neg li gi ble (less than 1 per cent) if the load is such as to have a VSWR of 1.2 to
1.0 or less. Good load re sis tors such as Bird TERMALINE Loads will give this neg li gi ble or un -
read able re flected power.
4-1
Figure 4-1
Zero Ad just ment Screw