By Dick Benson, W1QG A Contemporary Homebrew Transceiver with a Vintage Flair Blending a few vintage components with a major dose of today’s silicon produced this all band SSB/CW transceiver. It started while camping on Pismo Beach CA. Although the old rig I was using was still getting out, its quirks were really starting to get to me. The vigorous whacks to the case to restore operation were getting more frequent! A combination of poor construction and 20 years of portable use were taking their toll. For a moment, visions of an IC-706 danced through my head, but I quickly regained my sanity. The wish list entered in the log that foggy morning included: • continuous frequency coverage over HF range Figure 1—A clean front panel makes for an • modular construction for upgrades and service attractive and easy to use rig. The vintage • excellent frequency stability (not another analog vfo!) components used from the NCX-5 consist of the • good CW capability panel, case, s-meter, ssb filter, and knobs. • solid “air-worthy” performance • programmable for future enhancements ending code development. Then, there’s the task of keeping • built-in trans-match the digital EMI out of the receiver. However, the flexibility • 12V operation gained by using a processor makes it worthwhile. • make it reliable and make it pretty ! The PIC series of chips is a popular choice for control A few months later, a vintage National NCX-5 was applications. But if a processor is required, why not choose discovered at a local swap meet. It was love at first sight. one that is capable of doing DSP? A web search turned up The NCX-5 was the ideal size for comfortably housing the an excellent solution: the Motorola 56L811 processor required circuitry. The radio had a clean, functional, front evaluation board. The 56L811 has a micro-controller panel with a mechanical-counter style of frequency readout. architecture with a DSP core. The board comes with 32K of This was just perfect for the envisioned digital frequency program and data memory, plus a JTAG port for a debugger. display. How could one go wrong for $25? On-board EEROM can be programmed to boot the processor on power up. Features such as timers, serial & parallel IO ports, and flexible interrupt lines, are handy for the control Hardware: Processor portion of the design and go beyond what a typical DSP chip The decision to abandon the analog vfo virtually mandates provides. Interfacing the LCD display, shaft encoder and the inclusion of a processor. Taking this route has its share DDS hardware were a snap. The board also comes with an of pros and cons. Not only do you get to enjoy the RF audio CODEC. Fortunately it is easily disabled and is hardware development, but the opportunity to do never replaced with a high quality stereo sigma-delta ADC and DAC for this design. Hardware: RF Figure 3 shows the block diagram of the rig. It uses an up conversion strategy with a first IF of 46.0218 MHz. The first local oscillator covers from 46.0218 to 76.0218 providing dc to 30 MHz coverage. The LO consists of an Analog Devices AD9850 DDS with a 4-to-1 PLL forming a narrow-band tracking filter. The tracking filter is used to suppress DDS spectral spurs. The VCO covers the entire tuning range without tank circuit switching and this sets the phase noise performance. This straightforward LO performs very nicely. Figure 2—Although not as compact as today’s See Table 1 for more detailed information. commercial gear, the rig is built using standard RF bread-boarding techniques. It includes an A helical band-pass filter follows the high level first mixer integrated trans-match for portable operation. and is constructed from PCB material with 2 Air–Dux coils 6.0218 MHz Xtal Comlinear 30 MHz LPF 46 MHz Helical BPF SRA-173 BPF (NCX-5) NE602 GRA-3H e e CLC5523 Rcv Rcv g g diplexer Xmit e e Xmit 6.0218 MHz +/- 1.5 kHz Xmit Rcv +X Rcv NE602 46-76 MHz Xmit 11.5 to 19 MHz AD9850 AD9850 DDS DDS out out Antenna Matching Network RCV_AGC ANTENNA intfc clk intfc clk VCO 46-76 MHz Loop Filter 120 MHz Loop Xmit Filter Band Tune 1 Tune 2 out Rcv Full Wave Rectifier Fout=3xFin PR2 PF2 in +X Xmit g Rcv C 30 MHz LPF 40.000 MHz C Xmit +13 dB, 40 W out MAX512 3 CH DAC +14 dB 1 2 N G g RFPA N N Comlinear RCV MGC CLC5523 P-P 2SC1678 P-P MRF455 A I I MGC on RCV U PR1 PF1 E ALC on XMIT N C _ Xmit ALC A A out D R R level in CS 4328 Sigma-Delta Stereo DAC O +12V (Fs=9.765625 kHz) +X R F D R I V E V O +12V +15V +CW M G G DC to DC Audio Power Amp F +5V C N Convertor -5V M V -15V NF F +X N PC(14) P PB(2) 2 PC(0-3) CS 5389 Sigma-Delta Stereo ADC Debug M RS232 JTAG Port O IA R A U R IP P P P P S S S 1 MCU Earphone PC(15) "TIO2" E 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 PC(8-13) "SSI" A B C D 16:1 Analog MPX OUT T A A D L 32kx8 32kx16 32kx16 PC(5-7) "SPI" RefOut Mic Preamp W W W Q0Q1 Q2 Q3 F R F D 2R I V E F Data SRAM Pgm SRAM PB(4) +X Flash Mic Input O T PTT DSP56L811 G G PB(3) F C RESET M PC(4) 1 2 3 1 20.00 MHz F F NOTES: P Key M TiCK1 Keyer PB(0-1) S S S +X is generated by bit PB(2), "1" on Xmit M PB(5-15) O A DSP runs at 50 ns instruction cycle R O g amp with gain control 200 PPR Keyer Mode (PB) F=7.240000 Shaft W W W LSB TNR0023 Encoder amp with enable N e 16x2 OPTRONICS LCD Front Panel Controls 3 2 1 Figure 3— Block Diagram serving as the resonators. A -100 dB notch is carefully placed at the image frequency of 34 MHz. Although the Software helical filter does a respectable job, a 5 or 10 kHz wide The assembler, linker, and debugger supplied as part of the crystal filter would be a preferable solution. In spite of this evaluation kit by Motorola, were sufficient to develop the tradeoff, a high level 2nd mixer and optimized buffer software. The code consists of 4 major subsections: amplifier gives the radio a reasonable dynamic range. The 1. initialization of peripherals second IF is based around the NCX-5 crystal SSB filter 2. “main loop” for panel controls, LCD, S-meter etc. followed by two ComLinear CLC5523 amplifiers. The audio 3. shaft encoder interrupt service routine derived AGC drives the gain control ports of these 4. ADC / DAC interrupt service routine amplifiers. Finally, NE-602s are used for both receive and The bulk of the work in running the radio is performed in transmit balanced modulators. The LO injection signal is subsection 4. Both the receive and transmit audio signals are generated by a second DDS. The audio bandwidth signals to handled in this code segment. Also, the lower bandwidth and from the NE-602s are interfaced to the DSP with the signals from the front panel controls, AGC, etc. are acquired sigma-delta ADC and DAC subsystems. and stored for use by the main loop (section 2). In principle, to change from receive to transmit, one merely Ironic as it may seem, getting the transceiver to work well in reverses the signal flow through the AF, IF, and RF stages in CW mode was one of the biggest challenges. The NCX-5 the block diagram. Some of the stages (passive filters and SSB filter is 2.8 kHz wide. Without a genuine analog CW mixers) are naturally bi-directional The processor generated filter, obtaining good performance on CW is harder than one +X(mit) signal reverses the signal flow in several of the might think. It’s quite easy for the DSP to implement an active stages while other stages are simply by-passed. elegant audio filter, but all signals within the pass band of Most of the radio’s front panel controls and switches are the SSB filter are influencing the AGC level. An elaborate interfaced to the processor allowing the software to define scheme was conceived and implemented in the DSP code to the functionality of each one. The processor also monitors deal with this problem. The performance is not quite as good forward and reflected power, ALC, AGC, and the 12Vdc as a “real” CW filter, but adequate. Currently, the code power supply level. A 16-to-1 multiplexer feeding the executing during CW receive mode consumes the largest second channel of the sigma-delta ADC, is the interface fraction of the processor’s available horsepower. between these analog signals and the processor. CONSTRUCTION My son created a sturdy chassis frame out of aluminum angle stock in his high school metal shop. Double-sided PCB material is attached to the top of the frame and this forms the chassis. Holes in the frame for the controls align with holes in the front panel and the control bushings securely fasten the frame to the panel. Good shielding between the various modules is important. The modules must “communicate” over carefully controlled paths, not through the ether, control, or power wiring. A Figure 4—A top view of the transceiver with its variety of solutions were used including cast aluminum case removed. A few of the essential instruments boxes, enclosures fashioned from PCB material, and used for development are also visible. scavenged enclosures from a commercial RF synthesizer. The synthesizer enclosures have feed-through capacitors for What it took the dc and low speed control signals, and semi-rigid coax I/Os for the RF signals. An example of this useful enclosure The radio was christened on December 25, 1998 after about is shown to the left of the radio in Figure 4. 15 months of weekends and late nights. Another 5 months of code evolution produced most of the features I desired. As of The under side of the chassis (not shown) contains the DSP August ‘99, about 1000 contacts have been logged, board with ancillary support circuitry as well as the dc to dc including over 170 from Field Day. In short: it works, and converter supplying +15, +5, -5, and –15 volts. works well. Given the investment in parts and test equipment, one could Instrumentation certainly purchase a good commercial rig. But, ever since A good ‘scope and some bench power supplies are my first novice contact using a rock bound 6AG7+6LQ6 rig, necessary, but these instruments alone are not sufficient. “brewing” has remained my primary interest in ham radio. Figure 4 shows snippets of the instruments that fall in the Projects such as this are a great continuing education category of “don’t leave home with out them”: exercise and require gaining, or honing, a working knowledge in a broad range of disciplines. Plus, there is the • RF spectrum analyzer: undeniable satisfaction of using something of your own HP 141T 0.0l0–110 MHz with tracking generator crafting. • Audio spectrum/network analyzer + ac source: DSP Technology 50-21 dc-50 kHz • RF sources: 2 HP 8640s Futures • Logic analyzer: Arium ML4100 (not shown) The DSP capability provides the tantalizing opportunity for With the sole exception of the audio bandwidth signal more learning experiences. Transmit audio processing with analyzer, this gear was purchased at local electronic flea equalization and reverberation will be interesting. DDS markets. The total investment is under $2000. Good tools are control of the 1st and 3rd LOs allows pass-band tuning to be good investments, and these instruments will continue to implemented. Adaptive notch filters, AM demodulators, and serve and enlighten me for years to come. various receive filters will be fun to explore. Finally, the modular hardware construction allows for relatively painless frequency range 3-30 MHz transmit, 0.1-30 MHz receive improvements and experiments. architecture up conversion to 1st IF of 46.0218, second IF at 6.0218 1st l.o. 46 to76 MHz, DDS with x4 PLL to suppress DDS spurs l.o. Phase Noise –116 dBc/√Hz@20 kHz, flo=74 MHz, (rcving 28 MHz ) Acknowledgements 2nd l.o. 40.000 MHz (master timebase clock) Several people provided help and encouragement with this 3rd l.o. (bfo) DDS 6.0218 MHz ± 1.5kHz project. First, David DiCarlo, WB2LIV, at Motorola, tuning resolution 1,10,100,1000,5000 Hz steps using 200 ppr shaft encoder frequency control determined by a single crystal oscillator at 40.000 MHz. provided outstanding technical support. Other vendors of modes SSB, PSK31, CW semi QSK, built in keyer DSP hardware might take a lesson or two from Motorola. rcvr SFDR 84 dB, 28 MHz, 20 kHz spacing, (2.8 kHz SSB filter) And let’s not forget the failures and dead ends. In the good rcvr MDS -127 dBm SSB, -135 dBm CW as well as bad times, Foster Paulis, W4HCX, always had xmit Pout 40 W PEP, 100% duty cycle for PSK31 (small internal fan) words of encouragement and a genuine interest in the xmit IMD3 better than 30 dB below PEP at 40 W trans-match hi-Q bandpass characteristics, 40 dB harmonic suppression project. He generously provided some of the more elusive processor Motorola DSP56L811 (evaluation module), 20 MIPS components such as the shaft encoder, ferrite materials, and data conversion 16 bit sigma-delta ADCs and DACs for both rx and tx assorted silicon. Finally, thanks to my family for tolerating pwr requirement 12V at 1.5A receive, 12V at 10A transmit (key down) my obsession with this project. By the way, obsession is Table-1 Transceiver Technical Summary definitely a prerequisite to this game!
Pages to are hidden for
"A Contemporary Homebrew Transceiver with a Vintage Flair"Please download to view full document