MODEI_
LAC.A95
ANTENNA COUPLER INSTRUCTION MANUAL
LEADER ELECTRONICS CORP.
CONTENTS PAGE
SECTION
I 2
General Features
4
Precautions in Use
5
Control Functions
o
Use of the
Specifications
8 o
1 1
....
1
.
LAC-895
6.t Connections 6.2 MatchingAdjustments 6.3 Use of a Dummy Load in Matching 6,4 Measurement of SWR 6.5 In-line Power Measurements 6.6 Measurement of Reverse (Reflected) Power 6.7 Impedance Matching Range 6.8 Matching the Single Wire Antenna 6.9 Matching with Balanced Feeders ......, CircuitDesign 7,1 Functional Block Diagram 7.2 Metering Section 7.3 Antenna Matching Coupler Opening the Case Schematic
2
5
t2
14 15
!I
!
ANTENNA CoUPLER
1.
General
The LAC-895 is designed for use in amateur radio stations to achieve optimum matching between the transmitter and the antenna system. In addition, inJine power and SWR metering
facilities are included for output monitoring and SWR measurements.
2.
Features
'
Matching
for an SWR of 1.0:1.0 between rhe transmirter
(transceiver) and antenna is made possible.
'
Proper matching for single wire antennas used on one band, or multi-band operation.
' Perfect matching for maximum power ourpur. ' In-line type measuring circuit for direct power
output
readout.
' ' ' '
SWR measurements for use during matching adjustments. Suppression of spurious signals that cause BCI and TVI. Increases the
SiN (signal-noise ratio), and sensitivity at the
same time for receivers. Increases the driving power to the linear amplifier by properly matching impedances between input of linear amplifier and exciter.
' Two switch
positions, with the coupler out of the circuit,
for connection to direct output or a dummy
3.
1oad.
Specifications
Frequency
Range :
- 4.0MHz 2LO _ Zl.45MHz 7.0 - 7.3MHz 28.0 - 29.7MHz 14.0 - l4.35MHz
(1)
3.5
: 50S). Impedance : 50O, 75f,l coaxial
Input Impedance Load
Iess
cable,
at
SWR
than 5:1.
Power Handling
Capability
: Output
100W, continuous; 200W at
50/odtty.
In-line Power
Measurement : Two ranges:
20W and 250W at full
in forward direction. Power Meter Accuracy: !I0% of full scale. scale
SWR
Calibration : :
Power Requirement
1
to
10.
10W, minimum, for SWR measurements,
Insertion
Loss
:
Less than 0.5dB, dition. Type M. (U.H,F.)
at tuned con-
Connectors : Size and Weight : 150(H) x 200(W) x approx. 3 kg. 4.
Precautions
1.
in
200(D)mm;
Use
Power handling capability:
."'"
'*iil'i::::'iiJf
power outpur in use
-
keying: 200W SSB voice modulation: 500W pep transmitter 50% dvty, or CW
input
Higher operating powers should not be applied to prevent damage to the parts in circuit.
The output should be measured at the forward power condition.
(2)
Matching adjustments: When the matching circuit (coupler) is in circuit, the matching adjustments should be made with use of 1ow power, 10 to 20W, and within as short a time as possible.
After proper matching has been
achieved, higher
specified power may be applied. 5.
Control Functions
A.
Front panel, Fig. 1-A:
Fig. 1-A Front panel functions.
o
R TUNE:
/a\ \!)
X TUNE: For matching the antenna reactive
Used
in
matching the antenna resistive
^^mh^nanf
com-
Ponent. ,Zn
\,
BAND switch:
a.
Selects the amateur band
band is
in
use. The 3.5MHz
"split" for full band coverage, being at 3,5 and 3.8MHz; set as
broadly centered
required for proper matching.
(e)
b.
At DIRECT 1 or
DIRECT 2, the transmifier output can be routed to the antenna or dummy
load respectively to the DIRECT 1
and
DIRECT 2 connectors on the rear panel. The signal path is through the power meter circuir but the coupler is bypassed, see Fig. 5.
@
SET FULL SCALE adjuster: Used in SWR measurements to set the reference level on the SWR meter scale.
@
FUNCTION switch:
a,
FORWARD POWER: Selects
the full
scale
range, 20W or 250W.
b.
SWR: At SET, the adjuster 4 is used for full scdle setting.
At MEASURE, the SWR is read on the SWR scale.
@
Meter: With two
scales
for the forward power
and
one scale for SWR.
B,
Rear panel, Fig. 1-B:
/e\ Q
r.
Grounding terminai.
Connectors
@
TX:
For connection to the transmitter (transceiver)
ourpu!.
@
DIRECT 1 ANT oR DUMMY or dummt load connections.
@
DIRECT
2: Normally
nection.
@
Label.
(4)
used
LoAD:
for the
For antenna antenna con-
Fig. 1-B Rear panel connectors. Use of the LAC-895
6.1
Connections
The LAC-895 is connected between the transmltter (transceiver or exciter) and antenna as shown in tri- , ANTENNA
Fig. 2 LAC-895 connections.
(s)
1.
Transmitter output (antenna connector) to the TX connector: use a 50f) (or 52O) coaxial cable. The cable can be of any length. (Type of cable: 5D2V,
2.
8D2V, RG-8iU, RG-58/U, etc.) Coaxial cable from the antenna to the ANT (DIRECT 2) connector; the impedance can be of any value, 50,
3.
75 or 93Q. a 50S) dummy load with proper dissipation rating is available, connect to the DIRECT 1 connector; use
4.
Connect to a good ground; use heavy (large diameter)
If
a 50,f) cable.
wire.
6.2
MatchingAdjustments
IMPORTANT: The matching adjustments should be made at low output conditions. for example, at 10W.
A.
7, 14,21, and 28MHz bands: 1,. Control settings: BAND switch at the band in use.
"5". X TUNE dial at "5". SET FULL SCALE adjuster at full counterR TUNE dial at
clockwise.
FUNCTION switch at SWR MEASURE.
2.
Set the loading capacitor in the transmitter
at
maximum.
Turn on the transmitter and rapidly rotate the plate
3.
tuning capacitor for the dip in the plate current. Note the meter reading, rotate the R TUNE dial for a dip in the reading. Next, rotate the X TUNE dial for a further dip in the
(0)
meter,
Repeat the
R
and
X
adjustments
until the meter
reading is at or near 0 (zero). Under this condition, the LAC-895 is properly matched at 509.
NOTE: To raise the meter sensitivity, rotate the SET FULL SCALE knob in clockwise direction as
required. 4.
Set the FUNCTION switch at 20W or 250W, depending on the transmitter output
5.
rating.
Referring to the transmitter instructions, set the loading and plate tuning capacitors for maximum power output.
The WATTS scale on the meter should be observed during this operation.
B.
3.5MHz band:
1.
Two settings of the BAND switch, 3.5 and 3.8MHz, are provided for coverage of this band.
In
general, use 3.5MHz for the 3.5
and 3.8MHz for the 3.8
-
-
3.8MHz range
4.0MHz raflge' However,
if matching is possible. The matching adjustments are the same as either setting -...,'' "'-....b can be used
2,
given
above for the higher bands.
6.3
Use of a Dummy Load in Matching
When
a 50S2 dummy load is available, its use will
speed up the matching procedure.
1. 2. 3.
Connect the dummy load
to the DIRECT 1 con-
nector (at rear); use a 50S) cable. Set the BAND switch at DIRECT
1.
Set the FUNCTION switch at the power range to be used.
(7)
: 1
'{ I
4.
Adjust the loading and plate tuning capacitors for maximum output.
5.
Next, lower the transmitter output to about 10W for the adjustments to follow. NOTE: Do not touch the load and plate tuning capacirors.
6.
Set the BAND switch at the frequency band in use and make the adjustments
6,4
as
given in Sect, 6.2 above,
Measurement of SWR
The SWR can be measured durine or after
the
matching adjustments.
1. 2.
Set the FUNCTION switch at the SWR SET position.
Set the "SET FULL SCALE" adiuster at fu1l counterclockwise.
3.
The transmitter power (within the rating of LAC-895) is applied and the ,.SET FULL SCALE" adjuster is rotated until the meter reads at the ,.SET" mark on the SWR scale.
4. 6.5
Set the FUNCTION switch at SWR MEASURE and
read the value on the SWR scale. In-line Power Measuremenrs
The LAC-895 is designed to accurately measure the in-line power only when the load impedance is 50f2. Two
full
scale ranges, 2O and 250W, are provided as selected
with the FUNCTION switch. This power can be measured at all settings of the BAND switch, namely, through the antenna coupier, or the DIRECT connectors (to antenna or dummy load) and also in the SWR measurements. Note that
proper power measurements cannot be made when the 75f,2 cable is used in feedine the antenna.
(s)
F 6.6
Measurement of Reverse (Reflected) Power The LAC-895 is primarily designed
to
measure the
forward power, i.e. transmitter to the antenna. However, it is possible to measure the reverse power with the procedure given below.
1. 2. 3.
Set the FUNCTION switch at 20W or 250W,
de-
pending on the transmitter Power. Read and note the Power on the WATTS scale in use'
Adjust the "SET FULL SCALE" knob to fuli cou n terclockwi se.
4. 5.
Set the FUNCTION switch at S.W.R' SET'
Apply the transmitter power and slowiy rotate the "SET FULL SCALE" knob until the meter reading is the same as noted in SteP 2 above.
6. o./
Next, set the FUNCTION switch at SWR MEASURE' Read the reverse power on the WATTS scale in use'
Impedance Matching Range
The coupling circuit in the LAC-895 cannot be used to match with any value of antenna impedance' The reference impedance is 50S1. When the SWR is less than 5, in terms of a pure resistance, it corresponds to the 10 to 250S1 range.
However, since, the antenna is not a Pure resistance
and has a reactive comPonent, then with the two in combination, matching for an SWR = 1 can be done when the SWR is less than 5. When the SWR
greater than 5, matching is not possible, even when the R TUNE and X TUNE dials are adjusted for the lowest SWR indication. In this event, the
is
antenna must be adjusted. Use
(e)
of an antenna impedance
meter to measure the impedance will be of great heip,
In general, when matching adjustments are being made, the SWR need not be exactly 1.0. In practice, the SWR may be in the i,.l to 1,2 range without seriously 6.8
affecting transmission efficiency. Matching the Single Wire Antenna
It is possible ro use the LAC_g95 to match the single wire antenna to the transmitter, if the antenna impedance is in the 10 to 250O range. To meet with this condition, the antenna length should.be an odd number multiple of a quarter-wavelength, or
In TABLE
1,
Iisted.
f,
, where ), = wavelength.
for the different frequency bands
f,
TABLE
are
1
Frequency Band
0.95 x tr/4
3,535kH2
20.16 meters
7,050kH2
10.1
1
14.15MH2
5.04
2L.2MHz
3.36
28.5MHz
2.50
In practice, the actuai figure should be 0.95 x )./4, and the values are listed in the last column. (For the length in feet, multiply by 3.28.)
(i0)
SINGLE WIRE
ANTENNA
FROM
TRANSMITTER
ANT
TX 5O,fI
CABLE,
ANY LENGTH TO A GOOD GROUND SYSTEM'+r OR A COUNTERPOISE Fig.
3
Single wire antenna matching connections'
As shown in Fig. 3, the antenna lead is connected to the center terminal (socket) in the connector; use a banana
pl*g'
It
should noted that
a good grounding system
is
required. A heavy (large, diameter) wire should be used in
the connection to the ground terminal at the rear of the case.
In the event a good ground
is not availabie, then use a
counterpoise. The length should be equal to the value given in the last column of TABLE 1. After the proPer connections have been made, refer
to the matching procedures given in Sect' 6'2'
NOTE: The matching operation can be performed on
with different lengths, other than for the quarter-wavelength condition, as long as the impedance is in the 10 to 250,f) range' This applies'
antennas
for example, to the vertical tyPe antenna' 6.9
Matching with Balanced Feeders
The LAC-895 antenna coupler cannot be used directly with balanced feeders. However, as shown in Fig' 4' for the half-wave folded dipole antenna with the 300 ohm
(
11 )
feeder, a 300 ohm:75 ohm balun makes
che LAC-895 on
a
it
possible to use
balanced feeder arrangement. The
LAC-895 is designed, primarily, for use with unbalanced fee
ders.
HALF WAVE FOLDED DIPOLE ANTENNA
3OOS2
BALANCED FEEDER
4i.
BALUN TO LAC-895 ANT 75S' CABLE, ANY LENGTH
Fig.
4
Ba-lanced feeder
matching merhod.
For others, a suitable balun, such as a 200O:50f) balun for the 200S1 feeder, musr be used. When the 600S) balanced feeder is used, ir is possible to use the 300O:75O balun 7.
if
a smal1
amount of loss can be tolerated.
Circuit Design l.I runcrlonal SlocK Diagram I ne clrcults used are shown in Fig. 5.
The transmitter output connected to TX
passes
through the inline power and SWR metering section to the BAND switch, This switch selects the -od" of use, through
the antenna matching circuit, or direct to the antenna
input. 7.2
lletering Section The in-line type circuit is used in the power and SWR measurements, see SCHEMATIC.
The directional coupler is a wideband toroidal coil. Trimmer VC1 in the SWR detecting circuit is for
balance out the reverse power at SWR = 1.0, Diodes D1 and D2recti{y the forward and reverse voltages for meter indication. The in-line power meter indicates oniy the power in the forward
direction. VR1 and VR2, respectively, are for calibrating the 20W and 250W scales. 7.3
Antenna Matching Coupler The simplified circuit is shown in Fie. 6.
ANT
Fig.
6 Antenna coupler circuit.
In general, this is called the pimatching circuit. Since the input impedance is fixed at 50O, the input capaciror
is
fixed in value. At the antenna side, two variable capacltors, R TUNE and X TUNE respectively are used
to match the
I
I
l1--
(13)
resistance and reactive components condition.
for an
SWR
=
1.0
Opening rhe Case
The main cover can be taken off by removing the screws, two each at the sides and one at the top. For inspection of the in-line circuitry, the shield case can be opened by removing four screws
at each side and at the top. (Note: Circuit adjustments
should not be made unless absolutely required.)
(14)
4 I I a
It
SCHEMATIC
lc6
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3KV
17,
1 20w
FUNCTTO^i
? 2qw
Sr IJ 5L ll-_' I
I
4
BAND s2
rnT----o
GND
MEASURE
I I I
SCHEMATIC I
Modet LAc - 895 ANTENNA COUPLER
(1s) I
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n - qrq LEAO€R ELECTRONICS COPP.
