BIRD Thruline 43 User manual

iliiVQ
INSTRUCTION BOOK
THRULINE®
RF Directional Wattmeter
model 43

INSTRUCTION BOOK
THRULINE®
RF Directional
Wattmeter
model 43
mm
30303 Aurora Rd. Cleveland(Solon) Oh. 441 39

SUMMARY SHEET
Circuit
Measures
Insertion VSWR
Accuracy
Dimensions
Weight
Connectors
SO-ohm impedance -THHULINE
RF Power -5W to 5000W FuO Scale Direct Reading
in Watts, Frequency Range 2-1000 MHz in Si^ Std,
Element types, See Table 1, Section 4.
Less than 1.05 VSWR up to 1000 MHz
-5% of FulU Scale Power
Basic Overall 7'lg x 4^*w x3*‘h
4Pounds
Female and Male
Female and Male 'THN’*
Female and Male "C”
Most std. 50-ohm AN types
Not supplied on
regular orders
2Female Connectors standard with equipment,
unless otherwise specified*

TABLE OF CONTENTS
SECTION 1-GENERAL DESCRIPTION
Para^aphs ;Page
Purpose and AppUoation 1-1
2.
Description 1-1
SECTION 2-THEORY OF OPERATION
1* Travelling Wave Viewpoint 2-1
2. Coupling Circuit 2-1
3, Standing Wave Ratio vs* Reflected/Forward Power I^tio 2-1
SECTION 3-INSTALLATION
I* Portability 3-1
2, Connections 3«1
3, Remote Installation 3-2
SECTION 4-OPERATION
1. General 4-1
2, Load Power 4-1
3* Graph -^vs, 0and Its Significance 4-1
4, Measurement &Monitoring of Transmitter Power 4-4
5* Testing of Lines, Connectors, Filters, etc. 4-4
6. Frequency Response 4-5
7. Impedance Mismatch 4-6
SECTION 5-MAINTENANCE
1. Introduction 5-1
2. Trouble Shooting 5-1
3. CaUbratlon Checks -THHUUNF vs. TERMAUNi: Wattmeters 5-2
SECTION 6-PARTS LIST 6-1
LIST OF ILLUSTRATIONS
Figure: Page
1-
1View of Model 43 THHUUNE 1-0
2-
1Schematic Diagram 2-1
3-
1Outline Drawing, Model 43 THRULINE 3-1
3-2 Installation Drawing, RF Line Section 3-2
3-
3Panel Cut for Mounting RF Body 3-2
4
-
la Graph -Percent Reflected Power vs, VSWR (1*0 to 1.3) 4-2
4-lb Graph -Percent Reflected Power vs. VSWR (1,0 to 6,0) 4-3
4-
2Graph -Frequency Response 4-5
5-
1Parts Illustration 5-2
LIST OF TABLES
Table: Page
IRange of Element Types 4-6
n-IV Special Element Types 4-6
APPENDIX
Nomographs of Power Values vs VSWR Conversion

Il
Fig. 1-1. Model 43 THRULtNE
1-0

SECTION 1
GENERAL DESCRIPTION
1. PURPOSE AND APPLICATION
The Model 43 THRULINE Wattmeter is an inser-
tion tjrpe RF wattmeter, designed to measure power
flow and load match in 50-ohm coaxial transmission
lines. It is intended for use on CW, AM, FM, and
TV modulation envelopes, but not pulsed modes.
The Model 43, when used in 50-ohm applications,
has an Insertion VSWR of less than 1.05:1 up to a
frequency of 1000 MHz. The meter is direct reading
in watts, expanded down scale for easy reading, and
is graduated 25, 50, and 100 watts full scale. The
power ranges used are determined by the Plug-In
Elements, which fall in ten frequency band groups
covering from 2to 2300 MHz plus additional special
Elements in various power and frequency ranges
(see Section 4). Further characteristics may be
found in the Summary Sheet on page A.
2. DESCRIPTION
The Model 43 THRULINE, Figure 1-1, is aport-
able unit contained in adie cast aluminum housing,
with aformed metal enclosure on the back which is
easily removed. Included with the unit is aleather
earring strap, four rubber shock feet on the base,
and four rubber bumpers on the back, which allow
the Model 43 to stand or lie flat when used. For
additional protection, the microammeter is specially
shock mounted. Aslotted screw is provided on the
lower front face of the meter for zeroing the point-
er. Below the meter, the RF line section face pro-
trudes slightly from the wattmeter housing with the
Plug-In Element socket in the center.
Ashielded cable connects the microammeter to
the dc jack which is atUched to the side of the RF
line section casting. This cable, nearly three feet
long, permits removal of the RF Une section from
the Wattmeter housing. Meter connections may be
maintained with any installations outside of the hous-
ing. This permits permanent additional installations
to be made. See Section 3, INSTALLATION.
Inside the dc jack assembly, there is afilter ca-
pacitor which shunts the meter circuit to prevent
mis-readings caused by stray RF energy existing
in the Plug-In Element. Mounted on the dc jack is
aphosphor bronze spring finger, which protrudes
through alateral hole and into the Plug-In Element
socket of the RF line section. The finger has abut-
ton on its end which mates with the contacts of the
Plug-In Element. The nickel plated brass RF line
section is precision made to provide the best possi-
ble impedance match to the coaxial RF transmission
line in which the Model 43 is inserted. The ends of
the line section are nested in mating slots to provide
additional mechanical support.
At each end of the line section are Bird Quick-
Change type RF connectors, which may be quickly
interchanged with any other Bird ’'QC” connector by
removing the four screws on the mounting flanges.
The Wattmeter housing does not interfere with any
connector changes.
To make measurements, the cylindrical shaped
Plug-In Element is inserted into the line section
socket and rotated against one stop. Asmall catch
in the upper right hand corner of the casting face
presses on the shoulder of the Plug-In Element to
keep it in proper alignment and assure agood con-
tact with the dc jack and between the lower edge of
the Element and line section body. On diametrically
opposite sides of the Plug-In Element body are con-
tacts to provide dc pick-up in either direction.
These contacts make connection with the spring
finger of the dc jack only when the Plug-In Element
is in the precise forward or reverse position, and
with the index pin on the Element on the lower level
of the line section castingface against its respective
stop.
1-1

SECTION 2
THEORY OF OPERATION
1.
TRAVELLING WAVE VIEWPOINT
The best way to visualize the THRULINE idea is
from the TRAVELLING WAVE viewpoint on trans-
mission lines, which illustrates that the voltages,
currents, standing waves, etc., on any uniform line
section are the result of two travelling waves:
FORWARD WAVE travels (and its power flows)
from source to load, and has RF voltage Eand
current Iin phase, with E/I =Zo.
REFLECTED WAVE originates by reflection at
the load, travels (and its power flows) from
the load to source and also has an RF voltage
Cand current Jin phase, with CU »Zq ,
Note that each component wave is mathematically
simple, and is completely described by asingle fig-
ure for power, for instajice:
=Watts Forward «E^/Zq =I^Zq =El
WsWatts Reverse *€VZq =€J
Zo is the characteristic impedance of the uniform
line, and simplifies matters by being apure resis-
tance, usually 50 ohms, for useful lines. The main
RF circuit of the THRULINE is ashort piece of uni-
form air type line section, whose Zo is avery ac-
curate 50 ohms, in which correct measurements
may be made.
2.
COUPLING CIRCUIT
The coupling circuit which samples the travelling
waves is in the Plug-In Element. The circuitry of
the Element and its relationship to the other com-
ponents of the THRULINE are Illustrated in the
schematic diagram, Figure 2-1. Energy will be pro-
duced in the coupling circuit of the Element by both
mutual Inductance and capacitance from the travel-
ling RF waves of the line section. The Inductive
currents will, of course, flow according to the direc-
tion of the travelling waves producing them. The
capacitive portion of these currents is naturally
independent of the direction of the travelling waves.
Therefore, assuming that the Plug-In Element re-
mains stationary, it is apparent that the coupling
currents produced from the waves of one direction
will add in phase, and those produced from waves of
the opposite direction will accordingly subtract in
phase. The additive or ’’ARROW” direction is, of
course, assigned to the forward wave.
The electrical values of the Element circuits are
carefully balanced and so designed that the current
produced from the reverse wave will cancel the other
almost completely. The resultant is adirectivity
always higher than 30 dB, which means that the Ele-
ment is highly insensitive (nulled) to the ’’REVERSE”
direction wave. Being highly directional, the THRU-
LINE Element is sensitive (at one setting) only to
one of the travelling waves which produces standing
waves by Interference. THRULINE measurements
are therefore independent of position along standing
waves. It may be said that the THRULINE doesn't
know, doesn't care, and doesn't need to care where
it is along astanding wave.
3.
STANDING WAVE RATIO vs.
REFLECTED/FORWARD POWER RATIO
As mentioned above, the THRULINE technique
uses the TRAVELLING WAVE viewpoint to measure
most of the outstanding facts about transmission
line operation. Another widely used and related
viewpoint, is the STANDING WAVE, which is quite
elaborately developed both mathematically and In
existing equipment. This technique can be traced to
the early development of slotted lines as tools of
exploration.
The slotted line is astanding wave instrument,
and emphasizes this viewpoint. However, the slotted
line is too long, too expensive if good, not portable,
and slow in operation. These objections increase
rapidly as the frequency drops ^low 1000 MHz.
Whereas the THRULINE is surprisingly quick, con-
venient, and accurate by comparison. With the ex-
ception of phase angle reflection (distance, load to
minimum) it tells everything aslotted line will.
The relationships between TRAVELLING WAVES
and STANDING WAVE viewpoints are given in most
high frequency textbooks.
4
I
2-1

1SECTION 3
INSTALLATION
Fig. 3-1. Outline Drawing, Model 43 THRULINE
1. PORTABILITY
The Model 43 is aportable instrument, and the
housing is not designed for fixed mounting (see Out-
line Drawing, Figure 3-1). Astrap is provided for
carrying purposes.
While transporting the THRULINE it is best to
»re-insert the original Dust Plug, or aPlug-In Element
with the arrow pointed upward, in the measuring
socket, and secure with the catch. This will shunt
the meter circuit and serve to protect the meter by
dampening needle action during handling or shipping.
•Also, secure spare Plug-In Elements in their recep-
tacles with the pivoting knob clamps; just insert
Element to seat and twist knob one-quarter turn to
hold. Handle the Plug-ln Element with care at all
times. Calibration could be disturbed if they are
dropped.
CAUTION
Do not drop the THRULINE or its Elements or
subject them to hard blows. The microammeter is
shock mounted in the wattmeter housing, but its del-
icate mechanism may be damaged by severe impact.
2. CONNECTIONS
Insert the Model 43 THRULINE In coaxial trans-
mission lines of 50 ohms nominal impedance. It is
indifferent to which respective side the power source
and the load connections are made. If cables other
than 50 ohms are used, amismatch will occur
causing probable serious Inaccuracies in readings.
However, if amismatch cannot be avoided, the re-
sults may be calculated per paragraph 7of Section
4. We strongly urge that you avoid this condition.
The Model 43 is normally supplied with two Fe-
male N-Type connectors which are of the Bird
Quick-Change design. Other "QC" connectors are
available as listed:
3-1

Male N
Female HN
Male HN
Female C
Male C
Female UHF
Male UHF
7/8’* EIA Air Line
Female BNC
Male BNC
Female LC
Male LC
Female LT
Male LT
Female TNC
Male TNC
These may be purchased from Bird Electronic
Corp., as required. See Section 6, Parts List.
The above connectors are quickly changed by re-
moving the four #8-32 round head machine screws
from the corners of the connector flange, and pull
straight out. Reverse this procedure to attach con-
nector, making sure the center contact pin aligns
properly with the socket.
3. REMOTE INSTALLATION
The RF line section can be removed from the
meter housing for remote installation. To remove
the line section from Its housing:
a. Unscrew the six #8-32 flat head machine
screws holding the back cover.
b. Grasp the cover by the side filler tabs and pull
directly backwards. The back cover assembly
will come off with the speed nuts remaining
attached.
c. Remove the, two #10-32 oval head machine
screws on the front of the housing.
d. Slide the line section backwards out of the
housing. Do not loosen the two oval head
screws on the sides of the housing In line with
the meter. These hold the meter supporting
shock ring in place.
e. Substitute the cable which attaches the line
section to the meter with asufficient length of
cable to make the remote installation.
f. To replace the RF line section, reverse the
above procedure.
It may be desirable to have two or more line sec-
tions permanently installed in continuous operating
equipment. In this case, one set of Elements and
one meter may be used to measure several RF
transmission Unes WITHOUT INTERRUPTION OF
RF LINES for insertion of the THRUUNE. Addi-
tional RF line sections (Figure 3-2) are available.
Fig. 3-2. Installation Drawing, RF Line Section
The RF Line Section of the Model 43 blends very
readily to panel type mounting. Alayout for the
panel mount cut is given in Figure 3-3. The thick-
ness of the panel should be about 1/4 inch. On pan-
els less than this, build up the thickness with pads
or washers to achieve aflush-face mounting. Cable
connections are simplified because the RF line sec-
tion may be mounted in any convenient direction.
Attach the line section so that the finger catch is in
the most accessible position.
^RAO OR
45* CHAMFER
^(203)01A. DRILL
AND COUNTERSINK FOR
•10-32 F.H.M.S.-TW0 HOLES
Fig. 3-3. Pan«l Cot for Mounting RF Body
T
4
(
3-2

SECTION 4
OPERATION
1. GENERAL 2. LOAD POWER
The apparent features of the THRULINE equipment
have been discussed in Section 1, GENERAL DE-
SCRIPTION, and in the Instructions of Section 3,
INSTALLATION. Measurements are made by the
insertion and operation of the Plug-In Elements pre-
viously mentioned.
The Elements determine the power range to be
read on the meter scale, and the major markings
(viz. SOW, lOOW, etc.) are the FULL SCALE POWER
value for that Element. Elements are also marked
for FREQUENCY RANGE. The transmitter fre-
quency must be within the band of the Element used.
Elements are available according to those identified
in the tables on page 4-6.
Power delivered to (and dissipated in) aload is
given by:
=Watts into Load =\^ -\^
i.e., where appreciable power is reflected, as with
an antenna, it is necessary to subtract reflected
from forward power to get load power. This cor-
rection is negligible (less than 1percent) if the load
is such as to have aVSWR of 1.2 or less. Good load
resistors, such as our TERMALINES, will thus show
negligible or unreadable reflected power.
VSWR scales, and their attendant controls, for
setting the reference point, have been intentionally
omitted from the THRULINE for two reasons:
See paragraph 6of this chapter for frequency band
flatness, and performance of the Elements outside
of stated frequencies. Elements for additional ranges
(power or frequency) may be ordered without re-
turning the THRULINE for calibration, since the RF
bodies and meters are standardized, and are de-
signed for awide range of coaxial transmission
power values and frequencies.
ARROW on Plug-In Element indicates Sensitive
DIRECTION, i.e., the direction of power flow which
the meter will read. ARROW and REVERSE are
directional terms used in reference to the THRU-
LINE ELEMENT, and mean respectively the sensi-
tive and null directions of the Element. ROTATE
ELEMENT to reverse the sensitive direction. FOR-
WARD and REFLECTED are directional terms used
in reference to the source -load circuit. Note that
the transmitter may attach to either connector of
the THRULINE. It makes no difference which ex-
ternal RF connection is selected, since the Elements
are reversible and the RF circuit is symmetrical
end for end. Before taking readings be sure that the
meter pointer has been properly zeroed under no-
power conditions.
The THRUUNE used with aTERMAUNE resistor
of proper power rating forms ahighly useful absorp-
tion wattmeter. With ARROW set toward the load,
it is unnecessary to reverse because reflected pow-
er may be neglected.
In cases where readings are being made when the
meter unit is connected to an auxiliary RF line sec-
tion body, always remove any measuring Element
from the unused RF line section. Otherwise, the dc
circuit will be unbalanced or shorted according to
the arrow position of the other Element, causing in-
accurate or no reading on the meter.
(a) Why make something similar to ahypothetical
dc volt ohmmeter with control pots for the voltmeter
multipliers? Even more complications arise when
diodes at RF are Involved.
(b) Experience using the THRULINE on trans-
mitter tune-up, antenna matching etc., i.e., on OP-
ERATING PROBLEMS shows that the power ratio 0
is no mean competitor, in practical usefulness, to
the ratio /? =VSWR.
Atrial is suggested for afew days —forret VSWR
and try thinking in terms of 0=\^ /when the
THRULINE is used. It will be noted that, even with-
out bothering to calculate the ratio exactly, the two
meter readings and give an automatic mental
impression which pictures the situation. Thus, in
an antenna matching problem, the main thing usually
is to minimize ,and anything done experimen-
tally to this end is directly indicated when the THRU-
LINE is in the reflected position. Furthermore, the
ratio of readings, only mentally evaluated, is are-
liable guide to the significance of the remaining re-
flected power.
3. GRAPH-/? VS. <> AND ITS SIGNIFICANCE
Since there are definite simple relationships
p-ri2 where VSWB
and0= W
between standing wave ratio /O and the reflected/
forward power ratio 0indicate by the THRULINE,
the latter may be conveniently used to measure
VSWR. The relationship is given in Fig. 4- la and b.
4-1