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Interested in
shortwave
listening? This
active antenna
can really help
pull in those
overseas stations.
It comes as a kit
and can be put
together in a
few hours.
By GREG SWAIN
ACTIVE
ANTENNA
for the shortwave bands
Shortwave listening is a popular
pastime for many people and the
new receivers now available make
tuning into the world easier than
ever before. Unfortunately, making
the most of those weak signals from
across the world generally requires
a longwire antenna but that's not
always convenient.
There is another way and that is
to use an active antenna. The
"World Tuner AT4 SW" active
antenna described here uses a
1-metre telescopic antenna, a tuned
circuit, and two transistors to prevent loading of the antenna and to
boost signal output. It covers the
shortwave bands from 3-30MHz but
by plugging in an external inductor,
you can cover other bands as well.
The unit is disarmingly simple in
appearance. The circuitry is hous-
ed in a small plastic case and this is
fitted with a mounting base which
accepts the telescopic antenna.
When not in use, the antenna can
be telescoped down and stored out
of the way by fitting it to two plastic
P-clips on the back of the case.
The three user controls are arranged along one side of the unit.
They include a 4-position band
switch, a tuning control and a
power switch with LED indicator.
Also fitted to the unit are three
3.5mm jack sockets for external
antenna (EXT ANT), signal output
and external inductor (EXT L).
To use the unit, you simply connect the output to the antenna input
of the receiver, select the required
band and adjust the tuning knob for
best signal. What could be easier?
Because it can tune out interfering signals and noise, the "World
Tuner" can outperform many
longwire antennas. Often, it can
turn a station that is virtually
unreadable into a clear signal.
Alternatively, for even better performance, the unit can be used to
boost the performance of an existing longwire antenna via the external antenna input.
In short, the active antenna can
really help lift those weak stations
"up out of the mud". We tried it
with a Sony ICF-2001 shortwave
receiver with great success but the
unit will work well with any
receiver, particularly those that
lack sensitivity.
The circuit
Fig.1 shows the circuit details of
the active antenna. Normally, the
telescopic antenna is in circuit but
this is switched out if an external
antenna is plugged into the EXT ANT
18
SILICON CHIP
+3V
ON
S2b
OFF~
15pF
LEO1
ON
01
2N5485
02
BC548 C
L2
---=B+--1
220k
II
3V....?...
+
.,.
3.3uHII
II
1k
L3 1lffiS1a
6.8uHII
II -
52 ,
C
B
-20d8
VClb
A
1
1
.,. L4
60pF
11
louTPUT
15k
82!1
.,.
.,.
B
II
15uHII
100pF
-:.::o--.J
.,.
G<at>o ELJc
VIEWED FROM BELOW
WORLD TUNER
AT4 SW
Fig.1: signals from the antenna are fed to an input tuned circuit which is selected by S1a & Sib. Q1 and Q2 function as
buffer stages to prevent loading of the antenna tuned circuit.
jack socket. The signals picked up
by the antenna are fed via a 15pF
ceramic capacitor to a tuned circuit
consisting of either VCla or VClb
and either 11, 12, 13 or 14.
Slider switch S1 selects the band
to be tuned. There are four bands:
3-9MHz, 5-14MHz, 10-20MHz and
18-30MHz. When Sl is in position
A, 11 and VCla are selected and
the antenna can be tuned from
3-9MHz. Similarly, position B
selects 12 and VCla, position C 13
and VClb and position D 14 and
VCl b to tune the remaining bands.
Alternatively, an external inductor can be plugged into the EXT L
socket to extend the tuning beyond
those ranges provided. For example, plugging in a 47 µH inductor
(supplied with the kit) extends the
tuning range down to about
1.83MHz. A 560µH inductor will be
required if you want to cover the
AM broadcast band.
Note that when the external inductor is plugged in, it automatically disconnects the internal 15µH inductor. This means that Sl should
be switched to position A when using an external inductor.
FET Ql forms a high-impedance
buffer stage for the antenna tuned_
circuit. It is wired as a source
follower and so has a gain of a bout
0.75. Its output is fed to S2a, which
selects between OdB and - 20dB attenuation levels, and thence to the
base of Q2.
Q2 functions as an emitter
follower. DC bias for this stage is
set by the 10k0, 15k0, 4700 and 820
resistors. The signal output is taken
from across the 820 resistor and
coupled to the output jack socket
via a .OlµF capacitor.
Power for the circuit is derived
from two 1.5V batteries and is switched by S2b. LED 1 provides power
on indication but can be deleted if
you want to increase battery life.
Building it
This project is available as a kit
of parts (see panel) and is supplied
ready to assemble. The case even
When the unit is not in use, the antenna can be telescoped down and stored
by sliding it into two plastic P-clips on the back of the case.
JANUARY
1990
19
The two bottom terminals of the jack
socket are soldered directly to the
board while the third terminal is
connected using a wire link.
Most of the parts are mounted on a small PC board. Push all the parts down
onto the board as far as they will go before soldering their leads. The four
inductors are all mounted end-on.
~-----==----~f----CASE
WASHER/
,._____NUT
Fig.2: here's how to install the plastic
P-clips on the back of the case.
comes pre-drilled and silk-screened
to make the job as easy as possible.
The order of assembly is as follows:
• Step 1: fit the P-clips to the back
of the case [see Fig.2), then affix the
base weight to the case lid using
contact adhesive;
OUTPUT
• Step 2: screw the extension
shaft onto the tuning gang shaft.
Note: hold the flats on the tuning
gang shaft with a pair of pliers
when fitting the extension shaft,
otherwise you'll damage the gang.
• Step 3: assemble the PCB as
shown in Fig.3. Note that the tuning
gang and 3.5mm jack socket are
mounted on the copper side of the
PCB while the switches go on the
component side.
Before mounting the jack socket,
bend one of the terminals at the
rear of the jack socket through 90°
and then cut off the eylets of the
two terminals to be soldered to the
board. A soldering iron with a very
fine tip is required to solder the
socket terminal near the edge of the
board. The remaining terminal on
the rear of the socket is connected
to the PCB using a wire link.
Push the switches down as far as
they will go before soldering their
terminals. Inductors 11-14 are all
installed end on around Sl while
Q2 is laid flat against the PCB (see
photo). Install the LED so that its tip
is about 23mm above the surface of
the PCB [the longest lead is the
anode).
By the way, the four on-board inductors all look like resistors. They
have colour bands , just like
resistors, but are easily identified
because the fourth band is always
silver. The colour coding for each
value is listed in the table adjacent
to Fig.3.
• Step 4: install the batt6ry clip
EXTERNAL~
ANTENNA
lG -
1
CERAMIC & MONOLITHIC CAPACITORS
□
□
□
□
No
1
2
1
2
Value
0.1µF
.01µF
100pF
15pF
IEC
100n
10n
100p
15p
EIA
104
103
101
15
INDUCTORS
-
+ JV -
EXTERNAL
INOUCTOR
BATTERY
Fig.3: install the parts on the PCB as shown here. The
capacitor and inductor codes are shown in the
adjacent tables while the resistor values can be
checked using a digital multimeter.
20
SILICON CHIP
□
□
□
□
□
No
1
1
1
1
Value
47µH
15µH
6.BµH
3.3µH
1µH
Colour Code
yellow purple black silver
brown green black silver
blue grey gold silver
orange orange gold silver
brown black gold silver
PARTS LIST
The tuning capacitor is also installed on the copper side of the PCB and is
secured using the screws provided. The leads to the output and external
antenna sockets are run directly to the back of the board.
1 plastic case (pre-drilled &
screen printed)
1 metal weight for lid
1 telescopic antenna (1-metre
long)
1 antenna mount assembly
4 rubber feet
1 32mm-dia. knob
1 extension shaft
1 rubber cap (for external
4 7µ,H inductor jack)
2 P-clips
1 tuning capacitor
1 DPDT centre off toggle
switch
1 4-position slide switch
1 PCB, code Technikit WT401
3 3.5mm chassis sockets
3 3.5mm jack plugs
1 output lead
1 double AA battery holder
1 battery snap connector
1 solder lug
1 carry case (optional)
Semiconductors
1 2N5485 FET (01)
1 BC54 7 A transistor (02)
1 5mm red LED
Capacitors
1
1
2
1
2
4. 7 µF tantalum
0. 1µ,F monolithic
.01 µ,F monolithic
1 OOpF ceramic
1 5pF ceramic
RF chokes
1 4 7 µ,H (in jack plug)
1 1 5µ,H
1 6.8µ,H
1 3.3µ,H
1 1µ,H
The PCB is secured inside the case by installing the nuts on the toggle switch
and on the EXT L socket. Be sure to tighten the antenna base securely to
prevent it from turning when the antenna is installed.
lead (red to positive) by looping the
leads through from the copper side
of the PCB.
• Step 5: remove the washer from
toggle switch and install it on the
board mounted socket. Mount the
other two sockets adjacent to the Pclips on the rear panel and install
the antenna mount and solder lug
as shown in Fig.3.
Tighten the antenna mount screw
firmly. If you don't do it up tight
enough, the antenna mount will
twist when you screw in the
antenna.
• Step 6: complete the wiring as
shown in Fig.3, then mount the PCB
in the case (the washer on the EXT L
socket goes inside the case). Check
that the LED protrudes correctly
through the front panel and adjust
if necessary. Complete construction
by installing the nuts on the EXT L
socket and on the toggle switch, and
by screwing on the lid and rubber
feet.
Testing
The test procedure simply involves hooking the active antenna
Resistors
1 220k0
1 15k0
1 10k0
3 1k0
2 4700
2 820
Miscellaneous
Screws, nuts, washers,
insulation for battery holder
to a receiver and trying it out. To do
this, install the batteries and the
telescopic antenna, then plug in the
output ea ble and connect the other
end to the antenna inputs on the
receiver.
After that, you just select the required band (A, B, C or D), tune in
continued next page
JANUARY 1990
21
Silicon Chip
BACK COPIES
February 1988: 200 Watt Stereo Power
Amplifier; Deluxe Car Burglar Alarm; End
of File Indicator for Modems; Door Minder
Alarm; Low Ohms Adaptor for Multimeters;
Line Isolation Unit f,or Phone Patch;
Electronics In The Jaguar XJ40; Easy Tips
on Headphone Repair.
March 1988: Remote Switch for Car
Alarms; Telephone Line Grabber; Endless
Loop Tape Player; Build Your Own Light
Box; New Life for Radio-Cassette Players;
Old-Time Crystal Radio.
April 1988: Walkaround Throttle for Model
Railroads, Pt. 1 ; pH Meter for Swimming
Pools; Slave Flash Trigger; Headphone
Amplifier for CD Players; What is Negative
Feedback, Pt. 1 ; Mobile Antennas for the
VHF & UHF Bands.
May 1988: Optical Tachometer for
Aeromodellers; High Energy Ignition for
Cars; Ultrasonic Car Burglar Alarm;
Walkaround Throttle for Model Railroads,
Pt.2; Designing and Building RF
Attenuators; Motorola MC3334P High
Energy Ignition IC Data.
June 1988: Stereo Control Preamplifier
(uses LM833), Pt.1; Breakerless Ignition
For Cars Using Hall Effect Pickups; MegaFast Nicad Battery Charger; Automatic
Light Controller Uses PIR Detector; RF
Sniffer Probe & Preamplifier; What is
Negative Feedback, Pt.2.
July 1988: Stereo Control Preamplifier,
Pt.2; Fitting a Fuel Cut-Off Solenoid;
Booster for TV & FM Signals; The
Discolight Light Show, Pt.1; Tone Burst
Source for Amplifier Headroom Testing;
National Semiconductor LM833 Op Amp
Data; What is Negative Feedback, Pt.3.
August 1988: Building a Plasma Display;
Universal Power Supply Board; Remote
Chime/Doorbell; High Performance AC
Millivoltmeter (uses OP-27), Pt.1;
Discolight Light Show, Pt.2; Getting the
Most Out of Nicad Batteries; Data on
Insulated Tab Triacs.
September 1988: Hands-Free
Speakerphone; Switchmode Charger for
1 2V Gel Batteries; Electronic Fish Bite
Detector; High Performance AC
Millivoltmeter, Pt.2 ; Vader Voice; Motorola
MC34018 Speakerphone IC Data; National
Semiconductor LM12 150W Op Amp Data
& Application; What is Negative Feedback,
Pt.4.
October 1988: Stereo FM Transmitter
(uses Rohm BA 1 404); High Performance
FM Antenna; Matchbox Crystal Set;
Electronic House Number; Converting a
CB Radio To The 28MHz Band;
Electronics & Brock's BMW Blaster;
Queensland's Powerful Electric
Locomotives.
November 1988: 120W PA Amplifier
Module (uses Mosfets); Poor Man's
Plasma Display; Automotive Night Safety
Light; Adding a Headset To the
Speakerphone; How To Quieten the Fan In
Your Computer; Screws & Screwdrivers,
What You Need To Know; Diesel Electric
Locomotives.
December 1988: 120W PA Amplifier (With
Balanced Inputs). Pt.1; Diesel Sound
Generator; Car Antenna/Demister Adaptor;
SSB Adaptor for Shortwave Receivers;
Electronics & Holden's New V6 Engine;
Why Diesel Electrics Killed Off Steam;
Index to Volume 1.
January 1989: Line Filter for Computers;
Ultrasonic Proximity Detector for Cars;
Simple Computer Sound Repeater; 1 20W
PA Amplifier (With Balanced Inputs) Pt.1;
How to Service Car Cassette Players; The
Goalkeeper Gatling Gun; Massive Diesel
Electrics In the USA.
February 1989: Transistor Beta Tester;
Minstrel 2-30 Loudspeaker System; LED
Flasher for Model Railways (uses
LM3909); Build a Simple VHF FM Monitor
(uses MC3362), Pt 1; Lightning &
Electronic Appliances; Using Comparators
to Detect & Measure.
March 1989: LED Message Board , Pt.1 ;
32-Band Graphic Equaliser, Pt.1; Stereo
Compressor for CD Players; Map Reader
for Trip Calculations ; Amateur VHF FM
Monitor, Pt.2; Signetics NE572
Compandor IC Data; Electronics for
Everyone - Resistors.
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SILICON CHIP
April 1989: Auxiliary Brake Light Flasher;
Electronics for Everyone: What You Need
to Know About Capacitors; Telephone Bell
Monitor/ Transmitter; 32-Band Graphic
Equaliser, Pt.2; Led Message Board, Pt.2;
Fluke's New 80-Series Multimeters.
May 1989: Electronic Pools/Lotto Selector;
Synthesised Tom-Tom; Biofeedback
Monitor For Your PC; Simple Stub Filter
For Suppressing TV Interference; LED
Message Board, Pt .3; Electronics for
Everyone - All About Electrolytic
Capacitors.
June 1989: Touch-Lamp Dimmer (uses
Siemens SLB0586); Passive Loop
Antenna For AM Radios; Universal
Temperature Controller; Understanding
CRO Probes; Led Message Board, Pt.3;
Coherent CW - a New Low Power
Transmission Technique.
July 1989: Exhaust Gas Monitor (uses
TGS81 2 Gas Sensor); Extension For the
Touch-Lamp Dimmer; Experimental Mains
Hum Sniffers; Compact Ultrasonic Car
Alarm; NSW 86 Class Electrics; Facts On
the PhaxSwitch - Sharing Your Phone
Line With A Fax Machine.
August 1989: Build A Baby Tower AT
Computer; Studio Series 20-Band Stereo
Equaliser, Pt.1; Garbage Reminder - A
7 -day Programmable Timer; Introduction to
Stepper Motors; GaAsFet Preamplifier For
the 2-Metre Band; Modern 3-Phase
Electric Locomotives.
September 1989: 2-Chip Portable AM
Stereo Radio (uses MC13024 and
TX7376P) Pt.1; Alarm -Triggered
Telephone Dialler; High Or Low Fluid Level
Detector (uses LM1830N); Simple DTMF
Encoder (uses Texas TMC5089); Studio
Series 20-Band Stereo Equaliser, Pt.2;
Auto-Zero Module for Audio Amplifiers
(uses LMC669); A Guide to Hard Disc
Drives.
October 1989: Introducing Remote
Control; FM Radio Intercom For
Motorbikes (uses BA 1404 and TDA?000)
Pt. 1; GaAsFet Preamplifier for Amateur
TV; 1 Mb Printer Buffer; 2-Chip Portable
AM Stereo Radio, Pt.2; Installing A Hard
Disc in the PC; A Look at Australian
Monorails.
November 1989: Radfax Decoder For
Your PC (Displays Fax, RTTY and Morse);
Super Sensitive FM Bug; Build A Low Cost
Analog Multimeter; FM Radio Intercom For
Motorbikes, Pt.2; 2-Chip Portable AM
Stereo Radio, Pt.3; Floppy Disc Drive
Formats & Options; The Pilbara Iron Ore
Railways.
December 1989: Digital Voice Board
(Records Up To Four Separate Messages,
Uses Texas TMS3477NL and 256K
RAMs); UHF Remote Switch; Balanced
Input & Output Stages; National
Semiconductor LM831 Low Voltage
Amplifier IC Data & Applications; Install a
Clock Card In Your PC; Index to Volume
2.
Active antenna for shortwave listening
Because it can tune out noise, the active antenna can outperform a longwire
antenna. It can he used with virtually any shortwave receiver.
the wanted station on the receiver,
and adjust the tuning control on the
active antenna for best signal. You
should do this with the toggle
switch S2 in the " - 20dB" position
to make the signal peak more obvious. S2 is then switched to the
"ON" position to maximise signal
strength.
If overloading now occurs due to
excessive signal strength, return S2
to the " - 20dB" position.
Finally, don't forget to switch the
unit off when it is not in use to conserve the battery. The current con-
The metal weight is affixed to the
case lid to provide stability.
sumption when the unit is on is only
about 6mA so battery life should be
around 200 hours_
~
Where to buy the kit
A kit of parts for this project is available from Jiloa Pty Ltd. This kit includes all parts and is supplied with a pre-drilled case and a silkscreened front panel. Prices are as follows:
Complete kit of parts ............................................ $59.00 (incl. p&p)
Fully built & tested ....................................................... ..... $11 9. 00
Optional carry case ..... ...................... .................... ...... $1 0. 00 extra
Payment may be made by cheque or credit card number (Bankcard,
Mastercard, Visa) with mail order, or by quoting credit card number for
telephone order. Send your order to: Jiloa Pty Ltd, Technikit Division, PO
Box 73, Glenhuntly, Victoria 3163. Phone (03) 571 6303.
Note: copyright of the PCB artwork associated with this project is owned
by Jiloa Pty Ltd.
]ANUARY1990
23
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