A Contemporary Homebrew Transceiver with a Vintage Flair

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					  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!