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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. Use this handy form to order your back copies 11111\ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + ---7 Please send me a back issue for: 1- 1 May 1 988 rI October 1 988 n n June 1 988 November 1 988 I I March 1 989 1- l April 1 989 I i August 1989 □ September 1 989 □ February 1 988 □ March 1 988 □ D July 1988 D August 1 988 D September 1 988 □ December 1 988 D January 1989 □ □ May 1989 □ June D October 1989 February 1 989 □ July 1989 1989 □ November April 1 988 1 989 D December 1989 Enclosed is my cheque/money order for $ _ _ _ _ _ _ or please debit my □ Bankcard □ Visa Card □ MasterCard Signature _ _ _ _ _ _ _ _ _ _ _ _ _ Card expiry date _ __,__ _ Name _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ (PLEASE PRINT) Street_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ I Suburb/ town _ _ _ _ _ _ _ _ _ _ _ _ Postcode____ Price: $A5 .00 each (includes postage). Overseas orders add $A 1 .00 per issue for postage. NZ & PNG orders are sent by air mail. Detach and mail to: SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH NSW 2097 OR FAX: (02) 982 9553 X I ~--------------------------------------~22 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