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By JIM ROWE A low-cost, easy-to-build Planet Jupiter Receiver How would you like to try some basic radio astronomy – listening to the bursts of noise originating from the planet Jupiter, or from the Sun? You don’t need a lot of fancy equipment to do this, just the simple shortwave receiver described here. It’s hooked up to a basic dipole antenna (which we describe as well) and to the sound card in your PC, so that you can print out “chart recordings” of the noise signals. M ENTION THE TERM “radio astronomy” to most people, and they’ll either look completely blank or visualise huge arrays of steerable dish antennas – like the one at Narrabri in NSW. Of course, a lot of radio astronomy is done nowadays using these big arrays or huge ‘valley sized’ 32  Silicon Chip antennas like the one at Aricebo in Puerto Rico. But it’s still possible to do interesting observations using much simpler antennas and equipment, at “decametric” frequencies (8-30MHz) in the HF radio band. In fact, a NASA-sponsored project called “Radio Jove” has been promot- ing this type of radio astronomy for the last 10 years as a science project for high-school students and interested hobbyists. Over 1000 simple receiver kits have been sold, for 20.1MHz reception of noise bursts from the planet Jupiter, the Sun and other objects in the Milky Way galaxy. siliconchip.com.au There’s only one problem with the US-designed Radio Jove receiver as far as Australian students and hobbyists have been concerned: the receiver kits cost US$155 each plus shipping from the USA, so it will set you back about A$200 to have one sent over here. This has discouraged more than a handful of people in Australia from getting into radio astronomy. To encourage more Australian students and hobbyists to have a go, SILICON CHIP has developed its own low-cost receiver project. And that’s the background to the new receiver described in this article. You’ll find its basic specifications summarised in the “Main Features” panel but the bottom line is that it’s quite suitable for basic radio astronomy at decametric frequencies around 21MHz. This makes it fine for receiving noise bursts from Jupiter, the Sun or other sources in the Milky Way. We estimate that it will cost you around $75 for the basic receiver module, plus $7.30 if you decide to house it in an ABS instrument box. In other words, less than half the cost of the Radio Jove receiver. We also think it is a much better design, by the way. How it works The complete circuit for the receiver is shown in Fig.1. The heart of the circuit is IC1, an SA605D single-chip receiver IC which includes a local oscillator, an RF mixer, a high-gain IF amplifier and an IF limiting amplifier, plus a quadrature detector for FM signal demodulation. We are not using the last of these sections here, because we’re using the SA605 in a slightly unusual way – for AM signal demodulation. We do this by taking advantage of the chip’s RSSI (received signal strength indicator) output from pin 7. This works because associated with the high-gain IF amplifier and limiter stages inside the SA605 are a number of signal level detectors, whose outputs are combined to provide a DC output current from pin 7. This DC output current is logarithmically proportional to the incoming signal strength, so it is essentially an AM detector output. We convert it into a voltage signal by passing the current through a 91kW load resistor, shunted by a 470pF capacitor for low-pass filtering. The centre intermediate frequency (IF) of the receiver is set at 5.5MHz siliconchip.com.au The parts for the Jupiter Receiver are all mounted on a double-sided PC board. The top groundplane pattern is necessary to ensure stability. using ceramic filters CF1 and CF2. These require no alignment. The local oscillator circuit inside IC1 is brought out to pins 3 & 4, to which we connect frequency determining components L3 and VC3, together with 22pF and 39pF capacitors. Together, these components allow the local oscillator to be tuned manually over the range from 25.75-28.0MHz, which is 5.5MHz above the input signal range of interest (20.25-22.5MHz). The use of a 5.5MHz IF means that the receiver’s image frequency will be 11MHz above the wanted frequency – giving a good image rejection ratio. The input of IC1’s mixer stage is tuned to the centre of the wanted frequency band (ie, about 21MHz) by means of inductor L2 and trimmer Main Features The receiver is a single-conversion superhet design tuning from about 20.2522.5MHz, with a sensitivity of approximately 1mV for a 10dB signal-to-noise ratio. Only three controls are provided: RF gain, tuning and audio gain. All components are mounted directly on a small PC board measuring only 117 x 102mm, which can either be used “naked” or housed in a standard low-profile ABS instrument case (140 x 110 x 35mm). The receiver can be powered from either a 12V battery or a mains plugpack supply delivering between 15-18V DC. The current drain is typically between 55-75mA. There are two audio outputs from the receiver: (1) a line output suitable for connection to the line-level input of a PC sound card and (2) a low-impedance output capable of driving external headphones or a small 8W speaker. Both outputs can be used at the same time. August 2008  33 Parts List 1 PC board, code 06108081, 117 x 102mm (double sided, with plated-through holes) 1 plastic case, 140 x 110 x 35mm (optional) 2 Murata 5.5MHz ceramic filters (CF1, CF2) 3 mini RF coil formers (Jaycar LF1227) for L1-L3 1 300m length of 0.25mm enamelled copper wire 1 47mH RF choke (RFC1) 1 68mH RF choke (RFC2) 2 trimmer capacitors, 6.3-30pF (green) (VC1, VC2) 1 miniature tuning capacitor with edgewise knob (VC3) (Jaycar RV-5728) 1 50kW 16mm PC-mount linear pot (VR1) 1 50kW PC-mount 16mm log pot (VR2) 2 16mm-diameter control knobs 1 8-pin DIL socket (for IC2) 2 PC-mount RCA sockets (CON1, CON2) 1 PC-mount 3.5mm stereo jack (CON3) 1 PC-mount 2.5mm concentric DC socket (CON4) 1 TO-220/6093B heatsink 4 M3 x 10mm tapped spacers 5 M3 x 6mm machine screws 5 M3 nuts (two used as spacers for VC1) 2 M2.5 x 5mm machine screws (for VC1) 1 15 x 7mm copper sheet or tinplate (for IC1 shield) 1 14 x 10mm copper sheet or tinplate (for Q1 shield) 1 3.5mm mono jack plug to 3.5mm mono jack plug audio cable Semiconductors 1 SA605D single-chip receiver IC (IC1) capacitor VC2. The ‘Q’ of this circuit is fairly low, so that the receiver’s sensitivity is reasonably constant over the 2MHz wide tuning band. As a result tuning is achieved purely by adjusting the local oscillator frequency. Although the SA605 IC does provide a great deal of gain in the IF amplifier and limiter sections, we have included 34  Silicon Chip 1 LM358 dual op amp (IC2) 1 LM386 audio amplifier (IC3) 1 7812 +12V 3-terminal regulator (REG1) 1 78L05 +5V 3-terminal regulator (REG2) 1 BF998 dual-gate Mosfet (Q1) 1 PN100 NPN transistor (Q2) 1 3mm green LED (LED1) 1 3mm red LED (LED2) 1 1N4004 diode (D1) 1 16V 1W zener diode (optional) Capacitors 1 2200mF 16V RB electrolytic 1 470mF 25V RB electrolytic 1 330mF 16V RB electrolytic 1 22mF 16V tag tantalum 4 10mF 16V RB electrolytic 1 470nF MKT metallised polyester 8 100nF monolithic ceramic 1 47nF MKT metallised polyester 6 10nF monolithic ceramic 7 2.2nF disc ceramic 1 470pF disc ceramic 2 39pF NPO disc ceramic 1 22pF NPO disc ceramic 2 18pF NPO disc ceramic Resistors (0.25W 1%) 2 220kW 2 1.5kW 1 150kW 5 1kW 1 110kW 1 820W 1 100kW 1 360W 1 91kW 1 300W 2 47kW 1 220W 1 22kW 1 100W 1 10kW 1 47W 1 2.2kW 2 10W 1 1.8kW Antenna Parts 1 UB5 plastic box, 83 x 54 x 31mm 1 35 x 21 x 13mm ferrite toroid (Jaycar LO-1238) 50-ohm coaxial cable plus RCA plug for downlead an RF amplifier stage ahead of the IC to ensure that the receiver has adequate sensitivity. As you can see, this RF stage uses a BF998 dual-gate MOSFET (Q1), with the second gate (G2) voltage adjusted via VR1 to allow easy control of RF gain. The RF input signal from the antenna enters the receiver via CON1, and is fed into the input tuned circuit (L1/VC1) via an impedance matching tap on inductor L1. As before, the ‘Q’ of this circuit is kept relatively low, so once it’s tuned to about 21MHz it does not need to be changed. From the RSSI output of IC1, the demodulated audio signals are passed through op amp IC2a (half of an LM358) which is connected as a voltage follower for buffering. They then pass through a simple low-pass RC filter (the 1kW resistor and 10nF capacitor) before being fed to IC2b. This is the other half of the LM358 and is configured as an audio amplifier with a gain of 5.7 times, as set by the 47kW and 10kW feedback resistors. From IC2b, the signals pass through a 470nF coupling capacitor to VR2, the volume/audio gain control. They are then fed through IC3, an LM386N audio amplifier configured here to provide a gain of about 40 times. The amplified audio signals are then coupled via a 330mF output capacitor to speaker output jack CON3 and also to line output socket CON2 via a 1kW isolating resistor. Notice that the buffered RSSI signal from the output of IC2a is also fed to transistor Q2, which is used to drive LED2, the RSSI/overload indicator. Because Q2 does not conduct until the output voltage from IC2a reaches a level of around +2.65V, this means that LED1 really only lights when a very strong signal is being received, ie, when the receiver is tuned to a shortwave radio transmission or some other strong terrestrial signal source. So the main purpose of LED2 is to help you tune AWAY from such signals, rather than to them. Power supply The receiver’s power supply arrangements are very straightforward. Most of the circuitry operates from +12V, which can come directly from a battery if you wish. In this case regulator REG1 is not used but instead replaced by a 10W resistor. The 2200mF capacitor is also replaced by a 16V 1W zener diode, to protect the circuit from damage in case of higher-voltage transients (when the battery is being charged, for example). On the other hand, if you wish to operate the receiver from a 15-18V DC source such as a mains plugpack supply (Americans call them ‘wall warts’), this is very easy to do. In this siliconchip.com.au siliconchip.com.au August 2008  35 S(1) VC1 6-30pF 2.2nF 150k D(2) G1 G2 2x 2.2nF A K 470 F 25V IN GND 2200 F* 16V OUT REG1 7812 A K ZD1* 16V 1W +12V K A  B LED2 RSSI 100k IN GND OUT REG2 78L05  220 LED1 POWER 2.2k K A E C 39pF 39pF 91k 220k 10nF 100nF 100nF 8 47k IC2b 10 F 10k 6 5 8 10 11 470pF 12 100nF 220k 7 RSSI * ZD1 FITTED IN PLACE OF 2200 F CAPACITOR WHEN REG1 IS NOT USED (12V BATTERY OPERATION) 47 100nF +6V RFC2 68 H 1k Vcc 6 +6V IC1 SA605D 13 100nF 10nF 1k 14 LIM IN CF2 5.5MHz 820 17 16 15 IFA OUT 22 F TANT 300 5 MUTE 18 IFA IN 100nF 100nF 19 10nF 1k 10nF 1k RF IN2 LCL OSC B E 4 3 10nF 2 20 1 RF MXR IN1 OUT 10nF L3 1.2 H Q2 PN100 22pF 2.2nF VC2 6-30pF L2 1.8 H 10 F 21MHZ 'PLANET JUPITER' RECEIVER – + D1 1N4004 FIT 10  RESISTOR WHEN REG1 NOT USED (12V BATTERY OPERATION) +12V TUNING VC3 10-120pF 360 18pF 2.2nF 100 RFC1 47 H 1.5k 2 3 7 1 C B E PN100 AUDIO GAIN VR2 50k LOG 470nF 100nF IC2: LM358 4 IC2a 1 6 1 10 F 16V 4 A K OUT LEDS GND IN 7812 7 8 5 10 F 16V 1.5k K A K 1N4004 A ZD1 47nF 16V 10 330 F 1k 8 SPEAKER OUT CON3 AUDIO OUT TO PC CON2 CERAMIC FILTERS CF1 AND CF2 ARE MURATA SFSRA5M50BF00-B0 OR SIMILAR 10 CHAMFER SIDE OUT IC3 2 LM386N 3 +12V NOTCH 20 SA605D IN COM 78L05 Fig.1: the circuit is based on an SA605D single-chip receiver IC (IC1) which includes a local oscillator, an RF mixer, a high-gain IF amplifier and an IF limiting amplifier, plus a quadrature detector for FM signal demodulation. The latter feature is not used here. Instead, the SA605 is used in a slightly unusual way to obtain AM signal demodulation. SC 2008 15-18V (OR 12V) DC INPUT CON4 S D 2.2nF 1.8k Q1 BF998 47k RF GAIN 2.2nF 110k VR1 50k LIN 22k COIL DETAILS: L1, L2 & L3 all on Jaycar LF-1227 3mm diameter mini coil formers using 0.25mm enamelled copper wire, close wound at bottom of former. L1: 20 turns with tap at 4 turns from earth end L2: 20 turns L3: 15 turns NOTE: Ferrite slugs and shield cans are NOT used. 18pF L1 50  1.8 H RF INPUT CON1 G1(4) G2(3) BF998 +12V CF1 5.5MHz ANTENNA INPUT CON4 CON1 LINE OUT TO PC SPEAKER 15-18V DC OR 12V DC CON2 S T R IC1 SA605D 39pF 2.2nF VR1 A LED2 LED1 TUNING Table 1: Capacitor Codes 36  Silicon Chip Q2 PN100 VC3 22k IEC Code 470n 100n   47n   10n   2n2    470p   39p   22p   18p 1k 10nF RSSI case, REG1 is fitted to regulate the supply down to +12V, while a 2200mF capacitor is also fitted to provide the necessary filtering. The only part of the receiver which does not operate directly from the +12V line is IC1, which needs a supply of +6V. This is provided by REG2, a low-power 5V regulator arranged here to provide an output of +6V by means of the 300W/47W resistive divider across its output. LED1 is connected to the +12V sup- mF Code 0.47mF 0.1mF .047mF .01mF .0022mF       NA      NA   NA   NA 470nF 1 1.2 H RF GAIN Value 470nF 100nF 47nF 10nF 2.2nF 470pF 39pF 22pF 18pF 10 F 220k IC2 LM358 L3 50k LIN 1 47 470pF 100nF 10nF 22pF 2.2nF 39pF 6-30pF 1.5k 100nF + 1 VC2 68 H RFC2 5.5MHz 100nF 10nF 10nF + + 220 2.2k 18pF CF2 2x100nF 10k 47k 220k 100k 10nF L2 CF1 100nF 10nF 1k 1.8 H 100nF C02008 8 02 C 06108081T B18080160 100nF 820 1.5k 1k 5.5MHz 2.2nF 91k 2.2nF 300 78L05 100 22 F D S 10 F REG2 1k Q1 1.8k 2.2nF BF998 47nF + 10 2200 F 470 F K + 47 H RFC1 G2 G1 D1 10 F 110k 150k 360 2.2nF 47k 1k 330 F 4004 6-30pF 2.2nF VC1 18pF A CON3 A 10 F Tap L1 IC3 LM386 1.8 H A REG1 7812 EIA Code 474 104 473 103 222 470   39   22   18 POWER VR2 50k LOG AUDIO GAIN ply via a 2.2kW series resistor to provide power indication, while diode D1 is in series with the DC input to protect against reverse-polarity damage. Construction As you can see from the photos, all of the receiver’s parts are mounted on a small double-sided PC board measuring 117 x 102mm and coded 06108081. The board has platedthrough holes incidentally, to ensure good connections between the copper on each side – especially in the area of IC1, where a sound earth plane is essential for stability. All the input-output connectors are mounted along the rear edge of the board, while the controls and two indicator LEDs are mounted along the front edge. Note that tuning capacitor VC3 (a standard “mini” tuning gang with only one section used) is mounted upside down on the top of the board, with its edgewise tuning knob fitted under the board. Two 3mm nuts are used as standoffs between the capacitor body and the Fig.2: install the parts on the PC board as shown on this overlay diagram and the accompanying photo. Make sure that all polarised parts are correctly orientated. top of the board, to bring the knob up closer to the board. This is important if you want to fit the receiver into a low profile instrument case, because the knob will otherwise interfere with the bottom of the case. All the components mount on the top of the board, including IC1 and Q1 which are both surface-mount devices or “SMDs”. Although you need to be especially careful when fitting IC1 and Q1, building the receiver should be quite straightforward if you work carefully and use the board overlay diagram (Fig.2) and the photos as a guide. Here is the suggested order of assembly: (1) Fit connectors CON1-CON4 along the rear of the board. (2) Fit all of the resistors, taking care to fit the correct values in each position. (3) Fit the 8-pin socket for IC2, orientating it as shown to guide you in plugging in the IC later. Note that a socket is not used for IC3, as the LM386N is more stable when soldered directly into the board. siliconchip.com.au What Is Radio Jove? Radio Jove is a radio astronomy education project sponsored by NASA – the US Government’s National Aeronautics and Space Administration. Other organisations involved in the project are the University of Florida’s Department of Astrophysics, the University of Hawaii, Kochi National College of Technology, the INSPIRE Project and companies such as Raytheon, RF Associates and Radio-Sky Publishing. The goal of Radio Jove is to promote science education by observing and analysing radio signals emanating from the planet Jupiter, the Sun and our Milky Way galaxy. The project is directed primarily at high-school science classes, both in the USA and internationally, but interested hobbyists and radio amateurs are welcome to participate. The Radio Jove project has an office at NASA’s Goddard Space Flight Center and also has its own website at http://radiojove.gsfc.nasa.gov/ On this site there are a wide range of resources and reference materials, including observing guides and links to useful secondary sites. Radio Jove also sells kits for a simple radio receiver suitable for reception of “decametric” noise signals from Jupiter or the Sun, around 20.1MHz (14.915m). The kits cost US$155.00 each plus shipping (from Greenbelt in Maryland). An assembly manual for the receiver can be downloaded from the Radio Jove website, for those interested. (4) Now fit IC1 and Q1 to the board, taking the usual precautions with these SMDs. Use an earthed soldering iron with a fine chisel-shaped tip (very clean) and hold each device in position with a wooden toothpick or similar while you apply a tiny drop of solder (tack solder) to the diagonal end pins of the device, to hold it in position while you solder all of the remaining pins. The idea is to make each joint quickly and carefully, using a bare minimum of solder so you don’t accidentally bridge between adjoining pins. Also make sure you orientate Q1 correctly; this 4-pin device is very tiny but its source (S) pin is wider than the other three. Orientate the device so that this pin is at lower left, and tack-solder this pin first if possible. (5) Next fit trimmer capacitors VC1 and VC2, making sure their flat sides face the centre of the board. (6) After these, fit all the smaller fixed capacitors. These are not polarised Table 2: Resistor Colour Codes o o o o o o o o o o o o o o o o o o o o siliconchip.com.au No. 2 1 1 1 1 2 1 1 1 1 2 5 1 1 1 1 1 1 1 Value 220kW 150kW 110kW 100kW 91kW 47kW 22kW 10kW 2.2kW 1.8kW 1.5kW 1kW 820W 360W 300W 220W 100W 47W 10W 4-Band Code (1%) red red yellow brown brown green yellow brown brown brown yellow brown brown black yellow brown white brown orange brown yellow violet orange brown red red orange brown brown black orange brown red red red brown brown grey red brown brown green red brown brown black red brown grey red brown brown orange blue brown brown orange black brown brown red red brown brown brown black brown brown yellow violet black brown brown black black brown 5-Band Code (1%) red red black orange brown brown green black orange brown brown brown black orange brown brown black black orange brown white brown black red brown yellow violet black red brown red red black red brown brown black black red brown red red black brown brown brown grey black brown brown brown green black brown brown brown black black brown brown grey red black black brown orange blue black black brown orange black black black brown red red black black brown brown black black black brown yellow violet black gold brown brown black black gold brown August 2008  37 L1 16T L2 20T TAP 4T L3 A B 15T A B A B 1. BEFORE WINDING EACH COIL, REMOVE ENAMEL FROM END OF WIRE (5mm). THEN TIN AND WRAP IT AROUND TOP OF ONE PIN (A) ON UNDERSIDE OF FORMER. THEN SOLDER. 2. THEN WIND WIRE TIGHTLY AROUND FORMER FROM BOTTOM, WITH TURNS CLOSELY WOUND. 3. WITH L1, WIND 4 TURNS THEN LOOP OUT AND TWIST AS SHOWN TO MAKE 'TAP'. THEN WIND REMAINING TURNS. 4. WHEN ALL TURNS HAVE BEEN WOUND, CUT WIRE ABOUT 13mm FROM END OF LAST TURN. THEN REMOVE ENAMEL FROM LAST 5mm OF WIRE, TIN AND BRING DOWN TO WRAP AROUND TOP OF SECOND PIN (B) ON UNDERSIDE OF FORMER. THEN SOLDER. 5. REMOVE ENAMEL FROM OUTER END OF L1'S TWISTED LOOP 'TAP', THEN TIN SO IT CAN BE SOLDERED TO PAD ON PC BOARD WHEN COIL IS FITTED TO BOARD. Fig.3: follow these instructions to wind coils L1-L3. 15 x 7mm RECTANGLE OF COPPER FOIL OR TINPLATE ON TOP OF IC1 WIRES SOLDERED IN EARTH VIAS NEAR PIN 1 END OF IC1 1 SHIELDING PLATE FOR IC1 14 x 10mm RECTANGLE OF COPPER FOIL OR TINPLATE OVER CENTRE LINE OF Q1 S WIRES SOLDERED TO VIAS IN Q1 SOURCE COPPER, AT EACH END OF Q1 VERTICAL SHIELDING PLATE FOR Q1 Fig.4: here’s how to make and fit the shield plates for IC1 and Q1. apart from the 22mF tantalum capacitor which fits between the 1kW and 91kW resistors, just to the right of IC1. This capacitor is polarised, so make sure its positive lead is towards the front of the board. (7) Now fit the remaining electrolytic capacitors, which are again all polarised. The correct orientation of each electrolytic capacitor is shown clearly in the overlay diagram. 38  Silicon Chip These two photos show the shield plates for IC1 (above) and transistor Q1 (right). You can make the shield plates from either copper or tinplate. (8) Next fit RF chokes RFC1 and RFC2, which should both be about 2mm above the PC board. (9) Now fit the two ceramic filters CF1 and CF2, which are not polarised. (10) Follow these with transistor Q2, diode D1, REG2 and LED1 & LED2. Note that the green LED is used for LED1 and the red LED for LED2. LED1 is fitted first, with its leads bent down by 90° about 8mm from the body. It’s mounted with its body 6mm above the board surface. LED2 is then fitted with its leads bent down about 14mm from the body and so that it sits about 14mm above the PC board. (11) Fit REG1, if you are using it, noting that it is mounted on a small 6093B type heatsink. The regulator leads are bent down at 90° 6mm away from the device itself, so they can pass down through the matching board holes. Then the device and its heatsink are fastened to the board using an M3 x 6mm screw and nut, after which the leads are soldered to the pads under the board. (12) Fit IC3 directly on the board, orientating it carefully as shown in the overlay diagram. (13) Next, fit tuning capacitor VC3. As noted earlier, this fits upside down on the top of the board at centre front, with M3 nuts used as standoffs. The capacitor’s tuning knob must be removed from the spindle before it is mounted and only refitted once the capacitor’s leads have been soldered under the board. (14) Fit VR1 and VR2 (the RF and audio gain control pots). These first have their spindles cut to 10mm long and any burrs removed with a small file. Then each pot is fitted to the board, making sure that you fit the linear (B50k) pot in the VR1 position, and the log (A50k) pot in the VR2 position. Pass their pins carefully through the board holes as far as they’ll go comfortably (ie, without undue strain) and then solder them to the pads underneath. Then you can fit the control knobs to the pot spindles. (15) Wind the three tuning coils L1L3. As you can see from the data box in Fig.1, all three coils are wound on 3mm diameter mini coil formers (Jaycar LF-1227), using 0.25mm enamelled copper wire. In each case, the coils are close-wound at the bottom of the former, as shown in the small diagram of Fig.3. Oscillator coil L3 has 15 turns, while the other two have 20 turns each. The difference between L1 and L2 is that L1 has a “tap” four turns from the bottom. This tap is formed from a loop of the winding wire, twisted and tinned at the end so that it can be soldered to the appropriate pad on the PC board (just below CON1) when the coil is fitted. It’s a good idea to apply a small amount of clear nail varnish to the upper part of each coil, to hold it in place. (16) When the three coils are completed, they can be fitted to the board. When doing so, make sure you orientate each coil so that its “A” pin (connected to the bottom of the coil) mates with the earthy or “colder” pad on the board. The board overlay diagram has a small “A” next to each coil, to guide you in this regard. (17) Next, you need to make a couple of copper shield plates for IC1 and transistor Q1 to ensure stability. Fig.4 and the photos show how these plates are made and fitted (note: if you are unable to obtain copper foil, you can use tinplate or blank PC board). Both shields are attached using short pieces of tinned copper wire which go into adjacent holes in the PC board. (18) Finally, plug IC2 (LM358) into its socket, with its notched end nearer IC1. siliconchip.com.au The PC board fits inside a standard plastic case measuring 140 x 110 x 35mm. Note how the two LEDs are bent forwards, to go through their holes in the front panel. Your Jupiter Receiver board should now be complete and ready for switchon and set-up. Set-up Before applying DC power to the board via CON4, turn both VR1 and VR2 to their fully anticlockwise position. Then plug a small loudspeaker (8W) or a pair of stereo headphones into CON3, so you’ll be able to monitor the receiver’s operation audibly. When you then apply power, very little should happen initially apart from LED1 beginning to glow. If LED1 doesn’t light, odds are that you’ve connected the DC supply to the board with the polarity reversed. Now try turning VR2 clockwise slowly. You should begin to hear a gentle hissing sound in the speaker or one of the ’phones. If you have a DMM (digital multimeter), measure the voltage at pin 8 of IC2. It should measure very close to +12V if you’re using REG1, or +11.4V if you are powering the receiver from a 12V battery. Now measure the voltage at the rear end of RFC2 (ie, the end nearer REG2) which should be very close to +6V. siliconchip.com.au Finally, measure the voltage at pin 1 of IC2; this should be quite low – a few tens of millivolts. If you then turn VR1 clockwise, this voltage should steadily rise due to noise being amplified by Q1, as its gain is increased. The hissing sound in the speaker or ’phone should increase at the same time. If all is well so far, your receiver is very likely to be working as it should and you’ll be ready for setting it up. This mainly involves adjusting trimmer capacitors VC1 and VC2 so that the input and output circuits of the RF stage are tuned to around 21MHz. The easiest way to do this is if you have access to an RF oscillator or signal generator, able to deliver an amplitude modulated RF signal of 21MHz to the receiver’s input. The generator’s output is set to a level of about 100mV at first. Then you should turn up both VR1 and VR2 to about the centre of their ranges (‘12 o’clock’), after which you can slowly turn the knob of tuning capacitor VC3 up from its lowest setting, until you hear a 400Hz or 1kHz tone (the generator’s modulation signal). Now fine-tune VC3 carefully back and forth with your thumb, to achieve the loudest signal. If the sound becomes too loud or LED2 (the RSSI indicator) begins glowing, turn down VR2 and/or VR1 to reduce the gain. And if the signal is still too loud, try reducing the output level from the RF generator. Once you are sure that the oscillator is correctly tuned for reception at 21MHz, the next step is to carefully adjust trimmer VC2 with a small alignment tool, to again find the correct position for maximum signal. You may again need to reduce the generator’s output level, to prevent overload when you do achieve a peak. Once the correct tuning position for VC2 has been found, the last step is to adjust VC1 in the same way. In this case, you will almost certainly have to reduce the output level from the generator to prevent overload. In fact, by the time the tuning procedure is finished, the generator’s output should be wound down to a mere 1mV or so. No RF generator If you don’t have access to an RF August 2008  39 The antenna should be suspended as high as possible above the ground with a north-south orientation. This can be done by taping it to Nylon clothesline rope and running this between two high fixing points (eg, between a house gable and a mast). The balun and its connections are made waterproof by housing it in a UB5 jiffy box – see inset. generator, you’ll have to delay this tuning operation until you have built the receiver’s antenna, erected it outside in a suitable position and connected it to the receiver’s input so that it can provide you with some sort of signal – either a short-wave broadcasting station somewhere in the 20.25-22.5MHz range or just some atmospheric noise. More about this shortly, after we’ve talked about antennas. Antennas for 21MHz For reception of noise burst signals from Jupiter or the Sun in the northern hemisphere, the Radio Jove people recommend the use of a twin-dipole antenna array in which two halfwave dipoles are each aligned in an east-west direction and spaced about one half-wave apart, with them both suspended at least 3.6m above ground. The outputs of the two dipoles are combined using a phasing cable arrangement, to tilt the antenna’s main receiving lobe towards the south – because currently, Jupiter’s orbit is inclined somewhat south of the equator. In fact, the “declination” of its highest point (“transit”) in moving over the sky is about -20° in the Northern sky (ie, quite low towards the south). 6960mm 35mm OD x 13mm thick L15 toroid ONE END OF SECONDARY CONNECTED TO CENTRE CONDUCTOR OF COAX, OTHER END TO SHIELD BRAID (COAXIAL DOWNLEAD TO RECEIVER) CENTRE OF ANTENNA WIRE LOOPED THROUGH TOROID 6 TIMES, TO FORM PRIMARY OF BALUN. SIX LOOPS OF SAME WIRE PASSED THROUGH TOROID TO FORM SECONDARY WINDING. FOR BEST RESULTS SUSPEND ANTENNA AS HIGH AS POSSIBLE (>3.6m ABOVE GROUND), AWAY FROM METAL OBJECTS AND WITH A ROUGHLY NORTH-SOUTH ORIENTATION. Fig.5: this simple single-dipole antenna can be used with the Jupiter Receiver to receive Jupiter’s noise bursts. The dipole is cut to a length of 6960mm to make it resonant at close to 21MHz and is coupled to a coaxial downlead using a simple 1:1 balun made from a ferrite toroid. 40  Silicon Chip In the southern hemisphere, Jupiter’s orbit is currently much higher in the sky. In Sydney at the time of writing, the declination of its transit point is only slightly north of directly overhead and it’s predicted to take a couple of years before it swings significantly north. That’s because the cyclic period of Jupiter’s declination is almost 12 years and its southerly peak was earlier this year. All this means that for the next couple of years, in Australia and New Zealand it should be quite feasible to use a basic single-dipole antenna for reception of Jupiter’s noise bursts. Accordingly, we have produced and tested the very simple antenna design shown in Fig.5. It consists of a single length of multi-strand copper wire (we used one side of a length of figure-8 speaker cable), cut to a length of 6960mm (6.96 metres) to make it resonant at very close to 21MHz. This antenna should be suspended at least 3.6m above the ground and aligned as closely as possible to a north-south direction. I did this by taping it to a 6m length of Nylon clothesline rope, which was then run between a high point on the gable of my house and the top of a 3m mast, attached to the side of a workshop in the backyard. To couple signals from the antenna siliconchip.com.au to a cable running back to the receiver’s input, I made up a 1:1 balun (balanced to unbalanced transformer) using a small ferrite toroid as shown. This toroid uses L15 material and is 35mm in outside diameter, with a thickness of 13mm (Jaycar LO-1238 or similar). The centre of the antenna wire itself is looped through the toroid six times to form the primary winding of the balun, while a short length of the same type of wire is also looped through the toroid six times to form the secondary winding. To make the balun weatherproof and secure, I housed it in a little UB5 jiffy box (83 x 54 x 31mm), with the two ends of the antenna wire brought out through a 3mm hole on each side near the top. A BNC socket was then fitted to the lower end of the box, with the ends of the balun secondary winding connected to the socket inside. The downlead cable was connected to the socket on the outside, after the box lid had been screwed on. The whole thing was then hauled up on the Nylon rope, as it’s very light in weight. I used short strips of gaffer tape to attach the antenna wire and balun to the rope but Nylon cable ties would also be suitable. No-generator tune-up As mentioned earlier, if you don’t have access to an RF oscillator or signal generator it’s still possible to tune up the receiver reasonably well once you have an antenna to provide it with some signals in the vicinity of 21MHz. The way to do this is to connect the antenna, apply power to the receiver and set both VR1 and VR2 to their midrange (12 o’clock) positions, so you can hear a reasonable level of noise. Now try adjusting tuning control VC3 very slowly, to see if you can find a shortwave broadcasting station. I found a Chinese station at about 21.68MHz, for example – about twothirds of the way up the tuning range. If you do find a station, leave VC3 set to the position for clearest reception and then try adjusting trimmer VC2 very slowly and carefully with a small alignment tool. You should find a position which gives a peak in the signal’s reception but you may need to turn down gain controls VR2 and/or VR1 to lower the volume and prevent overload, so you can accurately find this peak. Once you are confident that VC2 siliconchip.com.au Decametric Radio Astronomy B ACK IN 1955, US radio astronomers Bernard Burke and Kenneth Franklin discovered that the planet Jupiter was a strong source of “noise burst” radio signals in the frequency range between about 8MHz and 40MHz – where the radio wavelength is in the tens of metres (hence the term “decametric”). They were using a “Mills Cross” antenna array, by the way, the design of which had been pioneered by Australian radio astronomer Bernard Mills of CSIRO’s Division of Radiophysics. The first Mills Cross had been built at Fleurs (about 40km west-south-west of Sydney) the previous year. It was soon discovered that the Sun itself is also a source of noise bursts during periods of sunspot activity and “coronal mass ejections” (CMEs). These solar noise bursts extend from the decametric range up to around 80MHz. The relative ease of receiving noise bursts from Jupiter and the Sun in the decametric frequency range using low-cost equipment seems to be why the Radio Jove project selected this range (rather than in the UHF or microwave regions). It should be noted though that because the signals are broadband in nature, the specific frequency used to receive the signals is not critical. The main requirement is to avoid frequencies occupied by international broadcasters and other terrestrial sources of radio signals. Useful websites A great deal of useful information on Jovian and Solar decametric radio astronomy – both theory and practice – can be found on the following websites: http://radiojove.gsfc.nasa.gov/ http://ufro1.astro.ufl.edu/dec-contents.htm http://www.jupiterradio.com/ http://www.radiosky.com/ The last of these sites is the source of the Radio-Skypipe software, which runs on a Windows PC and allows you to record noise data from a Radio Jove or similar receiver and print out “chart recordings” of them. There is a freeware version of the software which can be downloaded from this site. A useful source of skycharts and information on the rising and setting times for Jupiter (as well as many other astronomical bodies) in any specific location is: http://www.heavens-above.com/ An Australian site with useful information on solar storms and their effect on terrestrial radio conditions, etc is: http://www.ips.gov.au/ has been set correctly, leave both VC2 and VC3 with their current settings and turn your attention to VC1, the input circuit trimmer. Again it’s a matter of adjusting this very slowly and carefully until you achieve a signal peak, turning down VR2 and VR1 if necessary to prevent overload and distortion. What if you can’t find a shortwave station to help in this tuning-up procedure? That needn’t be a complete disaster, because if you have a DMM it’s possible to use a similar procedure using just the decametric “cosmic noise” being picked up by the antenna. To do the tuning up this way, set your DMM to a low DC voltage range (say 0-2V) and connect it to the re- ceiver to monitor the voltage at pin 1 of IC2. Then set tuning capacitor VC3 to the centre of its range and gain pots VR1 & VR2 to the centre of their ranges as well. When you apply power to the receiver, you should get a reading of 100-200mV or so on the DMM, as well as hearing the received noise in the speaker or ’phone. Now try adjusting VC2 slowly, first in one direction and then the other, to see if you can increase the DMM reading. Keep turning slowly in that direction, until the meter reading reaches a peak and then begins to drop again. Then return to the position where the reading peaks and leave VC2 in that position. If the DMM reading rises above about August 2008  41 There are just three controls on the front panel: an RF gain control, a tuning thumbwheel and an audio gain control. The RSSI (received signal strength indicator) LED lights when there is a signal overload (see text). 800mV, lower the RF gain by turning potentiometer VR1 anticlockwise, to bring the reading down again to 200mV. This will make it easier to see the peak reading on the DMM as you adjust variable capacitor VC2. After VC2 has been set to produce a peak in this way, leave it as before and follow the same procedure with VC1. Again turn down VR1 if necessary to prevent the DMM reading from rising above about 800mV. Once VC2 and VC1 have been set, your Radio Jupiter receiver should be tuned up about as well as possible without access to a generator. Fitting it to a case The PC board is designed to fit inside a low-profile plastic instrument case measuring 140 x 110 x 35mm. First, you will have to drill holes in the front and rear panels. Figs.9 & 10 show the front and rear panel artworks and these can be downloaded from our website, printed out and used as drilling templates. The board is secured to the two corner pillars at the back of the case using self-tapping screws, while the front of the board is secured to the front panel via the pot shafts and their nuts. Note that the board sits slightly proud of the front pillars in the case. Don’t attempt to screw the board down to these pillars (otherwise the board could crack). Testing with Radio-Skypipe To try out the new receiver and the Chart Started 11 June 08 by Jim Rowe in Sydney, Australia Fig.6: this recording chart covers almost the full period (about 11 hours) of Jupiter’s pass on the night of June 11, 2008 but shows very little evidence of signal bursts from Jupiter. Things were quiet around Jupiter that night! 42  Silicon Chip siliconchip.com.au siliconchip.com.au www.siliconchip.com.au 15-18V DC (OR 12V DC) ANTENNA SILICON CHIP LINE OUT TO PC SPEAKER TUNING POWER POWER RSSI RF GAIN also able to print it out as a pseudostrip chart recording – see Fig.6. As you can see, the recording covers almost the full period of Jupiter’s pass that night (June 11, 2008), because it rose at about 7pm, reached full transit at 2:07am and set again at around 9am the next morning. But the sky was very overcast that night, so perhaps that’s why there’s very little evidence of any bursts of signal from Jupiter. Either that, or things were pretty quiet around Jupiter that night. Looking around for some more information, I discovered that there are two different kinds of decametric noise burst from Jupiter: “L” or long bursts and “S” or short bursts. Both seem to be controlled by various factors, including which side of Jupiter is facing our way at the time and also the orbital position of Jupiter’s principal moon, Io. Sunspot and storm activity on the Sun also seem to play a role. They affect the way the Sun sends out streams of charged particles which can spiral RADIO JUPITER basic home-brew dipole antenna described above, I decided to download a copy of the “Radio-Skypipe” software which is recommended by the Radio Jove people. This is a data-logging application which runs under Windows 95/98/NT/2000/XP and can be configured to log data signals via either the ADC (analog-to-digital converter) in a standard 16-bit PC sound card or an external ADC. There’s a free-download version for non-commercial and non-government users and a Pro Edition with extra bells and whistles available for US$39.95, for commercial and serious users. I had no trouble installing the RadioSkypipe software on my old Win98 workshop PC and I was soon using it to take samples of the Jupiter Receiver’s audio signal twice every second. I then left it running so that it would log a complete pass of Jupiter over the following night. When I stopped the logging at 7.00am the next morning, I then saved the log file to the hard disk and was SILICON CHIP Fig.8 (left): the RadioSkypipe software has lots of logging options, including start and logging duration times. AUDIO GAIN Fig.7 (above): this screen grab from the Radio-Skypipe software shows a recording chart of the 21MHz signal for a 10-minute period. Fig.9: these artworks can be used as drilling templates for the case panels. around in Jupiter’s magnetic field. So it seems that there probably wasn’t much happening around Jupiter the night of my first logging run. The only way to find out is to keep trying, I guess. How about giving it a SC go yourself? August 2008  43