Fullscreen HTML5Med Res (??MB)HTML4

AMATEUR RADIO By GARRY CRATT, VK2YBX Build this simple HF receiver & tune into the 40-metre band This little receiver uses just two ICs and can tune the 40-metre band from 7MHz to about 9.4MHz. It can be built in an hour or so and when used with a suitable antenna, is capable of resolving AM, CW or SSB signals. This single chip design uses a minimum of components to provide quite useful results on any HF band. It is based on a circuit that was originally published in the ARRL magazine "QST" in September 1986, but our version includes several modifications. The basic concept of this new unit is similar to the Narrow Band FM Receiver described in the March 1989 issue. That unit was based on Motorola's MC3362 FM receiver chip. By contrast, this new design uses Motorola's MC3359 which is a low power narrow band FM IF strip. The MC3359 is used in virtually every VHF or UHF amateur transceiver made today. Fig.1 is a block diagram of the chip while Fig.7 shows the internal circuitry. As can be seen from these two diagrams, the MC3359 contains a crystal oscillator, a double balanced mixer, a 6-stage 455kHz limiter, a quadrature detector, an audio amplifier, and muting and scan control circuits. How it works Although the MC3359 is designed as an FM IF strip, it is possible to access a sufficient part of the internal circuitry to trick the chip into receiving AM, CW, and SSB signals. There are two points at which we can apply amateur ingenuity to accomplish this task, as discovered by Bruce Williams, WA61VC, Assistant Technical Editor of "QST" magazine. He found that the crystal oscillator, accessible at pins 1 and 2, could be used as a Colpitts (LC) oscillator. It could thus form quite a good VFO, there by enabling the receiver to be made tunable. ANTENNA AUDIO AMPLIFIER t------1i5 SCAN CONTROL - - - - f i 4 SQUELCH INPUT QUADRATURE 8 INPUT Fig.2: although the MC3359 is an FM IF strip, it can be "tricked" into receiving AM, CW & SSB signals. This diagram shows the configuration of the simple receiver described here. ◄ Fig.1 (left): block diagram of the MC3359 narrow band FM IF strip. It contains an oscillator, a double balanced mixer, a 6-stage limiter, a quadrature detector, an audio amplifier, and muting and scan control circuits. 92 SILICON CHIP I Our prototype receiver uses two ICs and tunes the 40-metre band from 7-9.4MHz. The receiver should be installed in a metal case and the tuning gang rigidly mounted to prevent tuning drift. Power comes from a 9V DC souce. performance can be optimised for CW, SSB or AM reception. For SSB reception, a CFU455H filter having a 6dB bandwidth of ± 3kHz is the best choice. Narrower filters will be more suitable for CW reception, while wider filters improve the AM reception. Fig.3 shows the various filter specifications. Having passed through the 455kHz filter, the signal is then fed Fig.2 shows how the MC3359 can be configured to form a simple amateur receiver. The incoming RF signal is connected to the input of the double balanced mixer where it is mixed with the VFO signal. The output of the mixer is at 455kHz and is fed via a 455kHz ceramic filter to the IF amplifier at pin 5. By selecting a 455kHz filter with suitable bandwidth, the receiver ■ Resin Molded Type 455KHz ---------■ Part Number General S e r ie s - - - - - - - - CFU455 D CFW455 [l e _~,,~ 't j: li u .t ,.. : ---r:; '~~ 4 2 1 Q_on nect1on 3 (f " Inp ut 12 . Ground 13' : Oulput CF V455 '.] .l I~ I I 2.9 2.9 2.0 - , ..; I o 5-; 1. 0 :~ 2.0 Connection ,1 . Input 2 3 ,4 · Ground ,5: Output 1.32.82.82.l lff+p;; S I ConneC\IOn ·1 · input ,2 J J · Grou nd (S · Output CFU CFW CFW455B CFU455B2 CFW455C CFU455C2 CFU455O2 CFW455O CFU455E2 CFW455E CFU455F2 CFW455F CFU455G2 CFW455G CFW455H CFU455H2 CFW4551 CFU45512 CFU455HT CFW455HT CFU4551T CFW4551T CFV455E CFV455E1O to the quadrature detector. While this is suitable for FM reception, it would appear at first glance to be quite unsuitable for AM or SSB reception. However, the internal configuration of this quadrature detector is similar to that of a double balanced mixer and can also be used as an AM detector! If a 455kHz BFO (beat frequency oscillator) signal is introduced to Stop Band Att. Att. 6dB (dB)min. Band Width Band Width (KHz ) min . (KHz ) max. CFU CFW 27 35 ±15 ±30 27 ±12.5 ±24 35 27 35 ±1 0 ±20 +15 + 7.5 27 35 :27 + 6 +12.5 35 + 4.5 25 35 ±10 25 35 ± 3 ± 9 25 ± 7 .5 35 ± 2 60 35 ± 3 ± 9 35 60 ± 7. 5 ± 2 +16 + 8 50 + 7.0 +12.5 50 Insertion Loss (dB) max . ln ./Output Impedance (KQ ) 4 4 4 6 1.5 1.5 1.5 1.5 2 2 2 2 6 6 6 6 2 1.5 1.5 6 6 6 6 2 • Stop band a11enuat1on ,s specified w, thm 455± lOOKH i • A 11enuat1on band width 1s spec1f1ed by 1he wid th of CF U : 40d8 . CFW : SOd B and CF V : 60d B. Fig.3: this table from the IRH catalog shows the characteristics of various ceramic filters and their pin configuration. Narrow filters are best for CW reception while wider filters are best for AM reception (see text). DECEMBER1989 93 68(! r------~----.....----<1---+-------WtA....-+9V ANTENNA 220 + 16VWr 22pF 18 180pF 17 120pF II L1:: II 16T VC2 8-1D0pF 150pF VCl 3-1DpF 1C1 390pFI +6V MC3359 .,. 10D(l S1 10 220 + 16VWJ 10 16VW + - 220 .,. II L3 II 1mHII .,. .,. G0o VIEWED FROM BELOW L1 : 16T, 268&S ENCU ON T37-6 FERRITE RING L2 : PRI 13T, SEC 3T, 268&S ENCU ON TS0-6 FERRITE RING SIMPLE 40-METRE RECEIVER Fig.4: the final circuit for the simple 40-metre receiver. Tuning capacitor VC2 is used to tune the VFO so that it is 455kHz higher than the wanted signal. The 455kHz signal from the mixer is filtered by FU and then fed via the IF amplifier to the detector. The output signal appears at pin 10 and is amplified by IC2. pin 8, the circuit thinks it is a product detector and is able to resolve SSB signals. Because the BFO has some tuning adjustment, the actual BFO frequency can be located close to one side of the IF passband thereby eliminating the beat signal on the other side of the passband. This means that if the receiver is built for 40-metre reception, the BFO should be tuned to allow reception of the 1SB signal (according to convention). If the receiver is built to receive higher frequencies, the BFO can be tuned for USB reception. Final circuit Fig.4 is the final circuit of our 40-metre band prototype. It shows the incoming signal fed from the antenna via a matching network to pin 18 of the MC3359. This is the input to the mixer. Tuning capacitor VC2 is used to tune the VFO so that it is 455kHz higher than the wanted signal. 94 SILICON CHIP The 455kHz output from the mixer appears at pin 3 and is fed via the 455kHz ceramic filter to the IF amplifier and then to the detector. There is insufficient audio at pin 10 of the chip to be of much use, so a simple audio amplifier using an 1M386 was used to increase the level to drive a small speaker. This produces adequate volume levels for normal listening conditions. S1 switches in the BFO for reception of SSB & CW signals. This switch applies DC volts to an MPF102 N-channel FET, which is configured as a Colpitts oscillator. The frequency determining element of the BFO is a 455kHz IF transformer (Tl) from a DSE coil pack (white). This transformer also couples the 455kHz signal from the BFO to pin 8 of the chip. The entire receiver draws less than 15mA and can be operated from a 9V battery. Zener diode ZDl ensures that the supply voltage is held at 6.2V. Construction All the parts with the exception of the tuning capacitor are mounted on a small PC board. This is coded SC06111891 and measures 121 x 53mm. Fig.5 shows the parts layout on the board. The order of assembly is not critical but be sure to keep component lead lengths to an absolute minimum. Pay particular attention when installing the ICs, zener diode and electrolytic capacitors. These are all polarised components and must be installed exactly as shown. Coil 13 is a commercial lmH choke (available from Dick Smith Electronics or Altronics) but you will have to wind 11 and 12 yourself. 11 consists of 16 turns of 26 B&S enamelled copper wire (ECW) evenly spaced on a T37-6 ferrite core. Clean and tin the ends of the winding before soldering the coil to the PCB. l ANTENNA VC2 -- 120pf ~ '" ~~ =!i + . 220pf 220µF,/ 001~ . . 0. 68k . A L30 ~ Hr . 01' 2 ,~ '" • • O 2~ - 0 VC3 ·+;.____:.=.__ ¥ ~ ""' 1 PCB, code SC06111891 , 121 x 53mm 1 TS0-6 Amidon ferrite ring or equivalent (ID 7mm, OD 13mm) 1 T37-6 Amidon ferrite ring or equivalent (ID 5mm, OD 10mm) 1 SPOT miniature toggle switch 1 miniature 8-ohm loudspeaker 1 1 OkO log potentiometer 1 CFU455H ceramic filter (see text) ,m~=:. . e 22pf e.()e180pf ~ ~~10uf PARTS LIST I + __:...:___ ___, ,r. 1- 0470 G:\ ill!} ~-·\; \\ 80 SPEAKER Semiconductors 1 MC3359 narrowband FM IF strip (IC1) 1 LM386 audio amplifier (IC2) 1 MPF102 N-channel FET (01) 1 6 .2V 400mW zener diode (ZD1) Fig.5: install the parts on the PCB as shown here, taking care to ensure that all leads are as short as possible. Use polystyrene capacitors where specified as these offer better stability. , Fig.6: this is the actual size artwork for the PC board. 12 has two windings of 26 B&S ECW on a T50-6 ferrite core. The primary winding consists of 13 turns while the secondary (on the antenna) side consists of three turns wound adjacent to one end of the primary. Note that one end of the secondary winding is kept free for connection to the an.tenna. The tuning gang and the board should be mounted in a metal case, with the tuning gang bolted in position. A stout length of tinned copper wire is used to make the connection to the fixed plates on the gang (note: make the connection to the largest section). Don't use a flexible lead for this connection if you do, the capacitance will vary as the lead is moved and this will detune the receiver. The tuning gang must be rigidly mounted for the same reason. Keep the connection between the gang and the PCB as short as possible (we simply lashed up the prototype to verify the circuit concept). Ceramic filters The parts list specifies a CFU 455H ceramic filter which has a 6dB bandwidth of ± 3kHz. This is ideal for resolving SSB but can also be used for CW. Alternatively, you could use a CFU4551/CFW455I ( ± 2kHz) for CW work only, or a CFU455E/CFW455E ( ± 7.5kHz) for AM reception. Other ceramic filters would also be suitable. If you use a 5-pin type, it can be glued to the copper side of the PCB and its leads connected to the pads using tinned copper wire. Alignment Alignment of the receiver is quite simple. First, the VFO must be ad- Inductors L 1 - 16T 268&8 ECW evenly spaced on Amidon T37-6 ferrite ring L2 - Primary 13T 268&8 ECW on Amidon TS0-6 ferrite ring; secondary 3T 268&8 ECW at one end of primary L3 - 1mH choke (DSE Cat. L 1820; Altronics Cat. L7046) T1 - 455kHz coil (white from DSE L-2060 coil pack) Capacitors 2 220µF 16VW PC electrolytic 1 1 OµF 16VW PC electrolytic 2 0.1 µF ceramic 1 .04 7 µF metallised polyester 2 .001 µF ceramic 1 390pF polystyrene 2 220pF polystyrene 1 1 80pF polystyrene 2 120pF polystyrene 2 1 OOpF polystyrene 1 33pF ceramic 1 22pF ceramic 1 3-1 OOpF tuning capacitor 2 3-11 pF trimmer capacitors (white - Altronics Cat. R-4003) Resistors (0.25W, 5%) 1 1OOkO 1 1 000 1 68k0 1 470 1 5600 1 100 justed so that it operates at 455kHz above that part of the HF band required. Its frequency can be checkDECEMBER 1989 95 r----------------------------------, ---------, ----------, I ., I II I·, 14 4 I I 77 I I I 18 11 16 I I I 10 ---+---e I I 33 k 33 k 33 k 3.5 k 7k 50 k 50 k 750 II 2.5 le I OSCILLATOR - I M IXER I OP AMP 8 ROADCAST DETECTOR I I I I I -------------------------------------------~-----------,I LI MITING IF AM PLIFIER DETECTOR ANO AFC I I I I I I I I I II s n-~---1----1 ~+----1-~~+====i:~~=t=====!====::t=:;;;;;;;:::::ii-J o1 33k 33k 10 33k k 33 k 0-4>-----+-..___..,___ _+-_ __.__ _......__......;......_.,___ 11 I 5k ......_.,__....._.~.,____........_J ___._ _ I s L---------------------------------~---------------------~ Fig.7: inside the MC3359. It contains an oscillator, a mixer, limiting circuitry, and a quadrature detector. ed by using a CRO (or sensitive frequency meter) to monitor pin 2 of !Cl. There will about 80mV p-p of signal here. Adjust trimmer VC1 so that when the tuning gang (VC2) is fully in mesh, the lower limit of the desired band plus 455kHz is displayed. For example, if you want the lower limit to be 7.0MHz, adjust VC1 so -that the frequency meter reads 7.455 MHz. This should now mean that with VC2 fully out of mesh, pin 2 will be at the upper frequency limit plus 455kHz. If you don't have a CRO or a frequency meter, a HF receiver and a suitable sniffer probe could possibly be used instead. The prototype covered the entire 40-metre band from 7.0MHz and extended up to about 9.4MHz, thus allowing reception of some shortwave stations. The BFO can now be adjusted. Its output frequency is best monitored Where to buy the parts The MC3359 is available from VSI Electronics in Sydney. Phone (02) 439 8622 (offices in all states). Murata ceramic filters are distributed by IRH Components (phone 02 648 5455). You can also try Dauner Electronics, DSE and Stewart Electronics. The L1 & L2 toroids are available 96 SILICON CHIP from Amidon stockists. Try R.J. & U.S. Imports, PO Box 157, Mortdale, NSW 2223; or Geoff Wood Electronics; or Truscott Electronics. The 3-1 OOpF tuning gang can . be obtained from Dauner Electronics. The Jaycar Cat. RV-5740 (0-160pF) and RV-5736 (0-1 00pF) types could also be used. at Ql 's source. Adjust Tl so that the output frequency of the BFO is close to one edge of the IF passband (ie, slightly less or slightly greater than 455kHz, depending on whether you wish to receive the LSB signal or the USB signal). Finally, trimmer capacitor VC3 in the antenna circuit should be adjusted for best reception. Antenna For best results, the receiver should be used with a long wire antenna, installed as high as possible. The prototype was able to receive many stations on 40 metres operating CW and SSB, as well as commercial AM shortwave transmissions. References (1). "The SIMPLEceiver", by Bruce 0. Williams, W A6IVC, "QST" magazine, September 1986. (2). Motorola Linear & Interface !Cs, 2nd edition, 1987. ~