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By Rick Campbell, KK7B A Binaural I-Q Receiver of QST Volume 1...consisting of a pair of audio phase-shift net-works and a summer ... binaural receiver that ... MN 56701-0677; tel

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Text of By Rick Campbell, KK7B A Binaural I-Q Receiver of QST Volume 1...consisting of a pair of audio...

  • 44 March 1999

    Ibuilt this little receiver to illustratean idea that Ive been exploring for anumber of years. It replaces thenarrow filters and inteference-fight-

    ing hardware and software of a conventionalradio with a wide-open binaural I-Q detec-tor. If you liken a conventional receiver to ahigh-powered telescope, this receiver is apair of bright, wide-field binoculars. Thereceivers classic junk-box-available-partsconstruction approach achieves better RFintegrity than that of commercial ham gear. APC board and parts kit is available for thosewho prefer to duplicate a proven design.1

    My goal was a project that could be con-structed in one weekend. With two workingparents and three teenagers in the house, thatone weekend wound up being spread overa period of about two months! Nevertheless,the total construction time was only 17 hours.There are a number of toroids to wind, andperformance was not compromised to sim-plify construction or reduce parts count.

    By Rick Campbell, KK7B

    A Binaural I-Q Receiver

    1Notes appear on page 48.

    Binaural I-Q ReceptionModern receivers use a combination of

    band-pass filters and digital signal process-ing (DSP) to select a single signal that is thenamplified and sent to the speaker or head-phones. When DSP is used, the detector oftentakes the form shown in Figure 1. The incom-ing signal is split into two paths, then mixedwith a pair of local oscillators (LOs) with arelative 90o phase shift. This results in twobaseband signals: an in-phase, or I signal,and a quadrature, or Q signal. Each of thetwo baseband signals contains all of the in-formation in the upper and lower sidebands.The baseband pair also contains all of the in-formation needed to determine whether a sig-nal is on the upper or lower sideband beforemultiplication. An analog signal processorconsisting of a pair of audio phase-shift net-works and a summer could be used to rejectone sideband. In a DSP receiver, the I and Qbaseband signals are digitized and the result-ing sets of numbers are phase-shifted andadded.

    The human brain is a good processor forinformation presented in pairs. We have twoeyes and two ears. Generally speaking, weprefer to observe with both eyes open, andlisten with both ears. This gives us depth offield and three-dimensional hearing that al-lows us to sort out the environment aroundus. The ear-brain combination can be used toprocess the output of the I-Q detectors asshown in Figure 2.

    The sound of CW signals on a binauralI-Q receiver is like listening to a stereo re-cording made with two identical microphonesspaced about six inches apart. The same in-formation is present on each channel, but therelative phase provides a stereo effect that isperceived as three-dimensional space. Sig-nals on different sidebandsand at differentfrequenciesappear to originate at differentpoints in space. Because SSB signals are

    composed of many audio frequencies, theysound a little spread in the perceived three-dimensional sound space. This spreading alsooccurs with most sounds encountered in na-ture and is pleasant to hear.

    To keep the receiver as simple as possible,a single-band direct-conversion (D-C) ap-proach is used. A crystal-controlled convertercan be added for operation on other bands,changing the receiver to a single-conversionsuperhet. Alternatively, the binaural I-Q de-tector can be used in a conventional superhet,with a tunable first converter and fixed-fre-quency BFO. If proper receiver design rulesare followed, there is no advantage to eitherdesign.

    The Receiver ProperFigures 3 through 5 show the complete

    schematic of the receiver. In Figure 3, signalsfrom the antenna are connected directly to a1 k GAIN pot on the front panel. J1, a BNCantenna connector, is used in keeping withmy VHF construction techniques theme.Adjusting the gain before splitting the signalpath avoids the need for a two-gang volumecontrol, and eliminates having to use sepa-rate RF and AF-gain adjustments. This vol-ume-control arrangement leaves the stereobackground noise constant and varies thesignal-to-noise ratio. The overall gain is se-lected so that the volume is all the way upwhen the band is quiet. Resistor values R9and R31 may be changed to modify the over-all gain if required. After the volume control,the signal is split with a Wilkinson dividerand connected to two SBL-1 diode-ring mix-ers. (The TUF-1 is a better mixer choice, butI had more SBL-1s in my junk box.) The VFOsignal is fed to the two mixers through a quad-rature hybrid, described by Reed Fisher.2 All

    A receiverwith presence...to fully appreciatethis receiver,youve got tohear it!

    Figure 1Simplified block diagram of areceiver using a DSP detector; see text.

    Figure 2Block diagram of an I-Qbinaural receiver that allows the ear-braincombination to process the detectoroutput resulting in stereo-like reception.

  • March 1999 45

    of the circuitry under the chassis is broad-band, and there are no tuning adjustments.

    The audio-amplifier design of Figure 4is derived from that used in the R1 High-Performance Direct-Conversion Receiver,3

    with appropriate simplifications. The R1high-power audio output is not needed todrive headphones, the low-pass filter iseliminated, and the diplexer has fewer com-ponents. Distortion performance is not com-promisedwell over 60 dB of in-band two-tone dynamic range is available. The originalarticle, and the additional notes in TechnicalCorrespondence for February 1996,4 de-scribe the audio-amplifier chain in detail.

    The VFOFigure 5 is the schematic of the receivers

    VFO, a JFET Hartley oscillator with a JFETbuffer amplifier. Components for the VFOtuned circuit are chosen for linear tuning from7.0 to 7.3 MHz with the available junk-boxvariable capacitor. Setting up the VFO is bestdone with a frequency counter, receiver andoscilloscope. The frequency counter makes iteasy to select the parallel NP0 capacitors andsqueezing and spreading the wire turns on L1achieves the desired tuning range. After thetuning range is set, listen to the VFO signalwith a receiver to make sure the VFO tunessmoothly and has a good note. Interrupt thepower to hear its start-up chirp. The signalmay sound ratty with the frequency counteron, so turn it off. The VFO is one area wherecraftsmanship pays off. Solid construction, aself-aligning variable-capacitor mounting,complete RF and air shielding and good ca-pacitor bearings all contribute to a receiver

    C43470 pF disc ceramicC44, C490.001 F metal polyesterC45, C46330 pF disc ceramicC47, C48220 pF disc ceramicC500.001 F feed-through capacitorJ1Chassis-mount female BNC connector

    Once my ears got used tothe effect, they had todrag me away from thisradio. This is one I gottahave!Ed Hare, W1RFI,ARRL Lab Supervisor

    Figure 3Front end and I and Q demodulators of the Binaural Weekender receiver. Unless otherwise specified, resistors are 1/4 W, 5%tolerance carbon-composition or film units. Equivalent parts can be substituted. Pin connections for the SBL-1 and TUF-1 mixers at U3and U4 are shown; the TUF-1 pin numbers are in parentheses. A kit is available (see Note 1). Parts are available from severaldistributors including Digi-Key Corp, 701 Brooks Ave S, Thief River Falls, MN 56701-0677; tel 800-344-4539, 218-681-6674, fax 218-681-3380; http://www.digikey.com; Mouser Electronics, 958 N Main St, Mansfield, TX 76063; tel 800-346-6873, 817-483-4422, fax817-483-0931; [email protected] mouser.com; http://www.mouser.com and Newark Electronics, 4801 N Ravenswood Ave, Chicago, IL06040-4496; tel 800-463-9275, 312-784-5100, fax 312-907-5217; http://www.newark.com.

    L51.6 H, 24 turns #28 enameled wireon T-30-6 powdered-iron core

    L6, L71.3 H, 21 turns #28 enameledwire on T-30-6 powdered-iron core

    L8350 nH, 11 turns #28 enameled wireon T-30-6 powdered-iron core

    R451 k panel-mount potT117 bifilar turns #28 enameled wire on

    T-30-6 powdered-iron coreU3, U4Mini-Circuits SBL-1 or TUF-1

    mixer

    that is a joy to tune.Both connections to the VFO compart-

    ment are made with feed-through capacitors.The power supply connection is self-explana-tory, but passing RF through a feed-throughcapacitor (at LO Out) may seem a bit unusual.Electrically, the capacitor is one element of alow-pass pi network. Using feed-through ca-

    pacitors keeps local VHF signals (high-pow-ered FM broadcast and TV signals near mylocation) out of the VFO compartment. Asecond pi network feeds the VFO signal tothe detector circuit below the chassis. The useof VHF construction techniques in a 40 meterreceiver may seem like overkill, but thepresent KK7B location is line-of-sight tobroadcast towers serving the Portland area.Using commercial HF gear with conventionalbypassing under these circumstances pro-vided disappointing results.

    The accompanying photographs show theprototype receiver. Receiver controls aresimple and intuitive. The ear-brain adjusts so

    naturally to binaural listening that I added aBINAURAL/MONO switch to provide a quickreminder of how signals sound on a conven-tional receiver. The switch acts much like theSTEREO-MONO switch on an FM broadcastreceivergiven the choice, it always ends upin the STEREO position on my receiver!

    The Koss SG-65 headphones identified inthe parts list and shown in the photograph arenot necessary, but they have some useful fea-tures. First, at $32, they are inexpensive.Second, they have relatively high-impedancedrivers, (90 ) so they can be driven at rea-sonable volume directly from an op amp. Fi-nally, they make an attempt at low distortion.Other headphones in the same price bracketare acceptable, but some have much lowerimpedance and wont provide a very loudaudio signal using the component valuesgiven in the schematic. Those $2.95 bubble-packed, throw-away headphones are not agood choice! Audiophile headphones arefine, but dont really belong on an experi-menters bench. A stray clip-lead brushingacross the wrong wire in the circuit can in-stantly burn out a driver and seriously ruinyour day.

    Building a Binaural WeekenderA few construction details are generally

    important, while others were determined bythe components that happened to be in myjunk box. The big reduction drive is delight-ful to use, but doesnt contribute to electricalperformance. I purchased it at a radio fleamarket. The steel chassis provides a signifi-cant reduction in magnetic hum pickup,something that can be a problem if the re-

  • 46 March 1999

  • March 1999 47

    What Do You Hear?Even the earliest solid-state direct-conversion (D-C) receivers had a presence or

    clarity that is rarely duplicated in more elaborate receivers. Many of us remember thefirst time we heard this crispness in a homebrewed D-C receiver. As we try toenhance our rigs through the addition of IF filters and other features, we still hopethat the result will be as clean as that first D-C receiver.

    This binaural D-C receiver is such an experiencebut even better. The binauralprocessing supplies the ears with additional information without compromising whatwas already there, enhancing the presence.

    As you tune through a CW signal on a quiet band (best done with your eyes closedwhile sitting in a solid chair), a centered signal enters, but moves to the left back-ground, undergoes circular motions at the back of your head as you tune through zerobeat, repeats the previous gyrations on the right side, fades to the right background,and finally drops away in the center. Multiple signals within the receiver passband aredistributed throughout this perceived space. With training, concentration on one signalallows it to be copied among the many. An SSB signal seems to occupy parts of thespace, left and right, with clarity when properly tuned, leaving others vacant. Staticcrashes and white noise appear distributed throughout the entire space without welldefined position. Receiver noise, although present, has no perceived position.

    Its vital that this receiver include a front-panel switch to shift between binauraland monaural output. Although useful during the learning process, it becomes indis-pensable for the demonstrations that you will want to do. I used the switch to set upmy son, Roger, KA7EXM, for the experience. We entered the shack and I handed himthe headphones. He put one phone to just one ear, but I told him that he had to useboth, that it would not work with just one. He put the phones on his head, casuallytuned the receiver through the 40-meter CW band, removed the phones and com-mented, Well, it sounds just like a direct-conversion receiver: A good one, but stilljust a direct-conversion receiver. I smiled and asked him to put the headphones onagain. As I flipped the switch to the binaural position his hand reached out, seekingthe support of the workbench. His facial expression became more serious. He easedinto the chair and began tuning the receiver, very slowly at first. After a minute hetook the headphones off, but remained speechless for a whilean unusual conditionfor Roger. Finally, he commented, Wow! The appliance guys have never heardthat!

    A builder of the Binaural Weekender should prepare for some truly unusual ex-periences.Wes Hayward, W7ZOI

    Close-up of the VFO. The simple VFO used in the prototype works exceptionally well, but must be completely shielded for good D-Creceiver performance. An empty mushroom can lives again as a VFO shield.

    ceiver is operated near a power transformer.(Steel chassis are available from parts housesthat cater to audio experimenters.) The VFOmounting and mushroom-can shield are asimple way to eliminate mechanical back-lash, keep radiated VFO energy off the an-tenna, prevent hand capacitance from shift-ing the tuning, and reduce VFO drift causedby air currents.

    Experienced builders can duplicate thisreceiver simply using the schematic and con-struction techniques shown in the accompa-nying photographs. Unlike a phasing re-

    ceiver, there is no need to precisely duplicatethe exact amplitudes and phases between thetwo channels. The ear-brain combination isthe ultimate adaptive processor, and itquickly learns to focus on a desired signaland ignore interference. Small errors in phaseand amplitude balance are heard as slightshifts in a signals position. Standard-toler-ance components may be used throughout. Akit version is also available (see Note 1).

    One note about the kit version: A verygood VFO can be built on an open PC boardif the variable oscillator is not running on the

    Figure 4The receivers audio-amplifierdesign is derived from one used in theR1 High-Performance Direct-ConversionReceiver (see Note 3), with appropriatesimplifications.C1, C15, C18, C21, C35, C38220 pF

    disc ceramicC2, C9, C10, C22, C29, C301 F

    metal polyester (Panasonic ECQ-E(F)series)

    C3, C231.5 F metal polyester(Panasonic ECQ-E(F) series)

    C4, C246.8 F, 16 V electrolytic(Panasonic KA series)

    C5, C19, C25, C3933 F, 16 Velectrolytic (Panasonic KA series)

    C6, C7, C8, C16, C26, C28, C27, C3610 F, 16 V electrolytic (PanasonicKA series)

    C11, C12, C31, C32100 F, 16 Velectrolytic (Panasonic KA series)

    C13, C14, C17, C20, C33, C34, C37,C400.1 F metal polyester(Panasonic V series)

    C41, C42, C500.001 F feed-throughcapacitor

    J21/8-inch stereo phone jackL1, L33.9 mH Toko 10RB shielded

    inductorL2, L4120 mH Toko 10RB shielded

    inductorQ1-Q62N3904RFC1, RFC210 turns #28 enameled

    wire on Amidon ferrite bead FB 43-2401 (six-hole bead shown in photos)

    S1, S2SPST toggle switchU1, U2NE5532 dual low-noise high-

    output op amp

    desired output frequency. The Kanga kit VFOruns at one-half the desired RF frequency,and is followed by a balanced frequency dou-bler and driver amplifier.

    Other ExperimentsMy earliest experiments with binaural

    detectors feeding stereo audio amplifierswere done in 1979, using two antennas. Thetechnique works very well, but requires twoantennas either physically spaced some dis-tance apart, or of different polarization. Lis-tening to OSCAR 13 on a binaural receiver

  • 48 March 1999

    with cross-polarized Yagis was an unsettlingexperience. The need for two antennas is aliabilitythese days, most of us struggle toput up one. A number of experiments havealso been done with binaural independentsideband (ISB) reception. These are pro-foundly interesting for AM broadcast recep-tion, and could be used for amateur AM orDSB reception using a Costas Loop for car-rier recovery. Binaural ISB detection ofshortwave AM broadcasting can be analyzedas a form of spread spectrum with the ear-brain serving the despreading function, or asa form of frequency diversity, with the ear-brain as an optimal combiner.

    The binaural techniques described hereare analogous to binocular vision: Theypresent the same information to each ear, butfrom a slightly different angle. This providesa very natural sound environment that thebrain interprets as three-dimensional space.There are other binaural techniques thatinvolve the use of different filter responsesfor the right and left ears. My experimentswith different filter responses for the left andright ears have not been particularly interest-ing, and I have not pursued them.

    SummaryThis little receiver is a joy to tune around

    the band. It is a serious listening receiver,and allows digging for weak signals in awhole new way. Digging for weak signals ina three-dimensional sound field is some-times referred to as the cocktail party ef-fect. It is difficult to quantify the perfor-mance of a binaural receiver, because thefinal signal processing occurs in the brainof the listeneryou. The experimental lit-

    erature of psycho-acoustics suggests that theear-brain combination provides a signal-to-noise advantage of approximately 3 dBwhen listening to speech or a single tone inthe presence of uncorrelated binaural noise.The amount of additional noise in the oppo-site sideband is also 3 dB, so it appears thatthe binaural I-Q detector breaks even. Insome applications, such as UHF weak-signal work, the binaural I-Q detector mayhave an advantage, as it permits listening toa larger slice of the band without a noisepenalty. In other situations, such as CWsweepstakes, the cocktail party may getentirely out of hand. Binoculars and tele-scopes both have their place.

    Notes1The complete kit version, available from Kanga

    US, uses a different VFO circuit than the oneshown here. The kit VFO runs at one-half thedesired output frequency, and is followed by abalanced frequency doubler and driver ampli-fier. Price: Receiver and VFO PC boards withall board-mounted components, $115 plusshipping. Contact Kanga US, Bill Kelsey,N8ET, 3521 Spring Lake Dr, Findlay, OH45840; tel 419-423-4604; [email protected];http://www.bright.net/~kanga/.

    Steel chassis such as the Hammond 1441-12 (275 inches [HWD]) with 1431-12 bottomplate and the Hammond 1441-14 (295inches [HWD]) with 143-14 bottom plate aresuitable enclosures. These chassis and bot-tom plates are not available in single quantitiesdirectly from Hammond, but are available fromAllied Electronics, 7410 Pebble Dr, Fort Worth,TX 76118; tel 800-433-5700, http://www.allied.avnet.com; and Newark Electronics,4801 N Ravenswood Ave, Chicago, IL 06040-4496; tel 800-463-9275, 312-784-5100, fax312-907-5217; http://www.newark.com.

    2Reed Fisher, W2CQH, Twisted-Wire Quadra-ture Hybrid Directional Couplers, QST, Jan1978, pp 21-23. See also IEEE Transactions

    C51, C52150 pF, NP0disc ceramic

    C5330 pF air-dielectricvariable

    C54, C554.7 pF NP0 discceramic

    C56, C57, C59, C610.1 Fmetal polyester (PanasonicV series)

    C5710 pF NP0 discceramic

    C600.001 pF metalpolyester

    C62, C630.001 F feed-through capacitor

    D11N4148L91.5 H, 22 turns #22

    enameled wire on T-37-6powdered-iron core; tap 5turns from ground end.

    L10350 nH, 11 turns #28on T-30-6 powdered-ironcore

    Q7, Q8J310 (U310 used inprototype)

    RFC310 turns #28enameled wire on Amidonferrite bead FB 43-2401(six-hole bead used inprototype)

    T210 trifilar turns #28enameled wire on Amidonferrite bead FB 43-2401(six-hole bead used inprototype)

    MTT, Vol MTT-21, No. 5, May 1973, pp355-357.

    3Rick Campbell, KK7B, High-Performance Di-rect-Conversion Receivers, QST, Aug 1992,pp 19-28.

    4Rick Campbell, KK7B, High-Performance,Single-Signal Direct-Conversion Receivers,QST, Jan 1993, pp 32-40. See also Feedback,QST, Apr 1993, p 75.

    ReferencesRick Campbell, KK7B, Direct Conversion Re-

    ceiver Noise Figure, Technical Correspon-dence, QST, Feb 1996, pp 82-85.

    Campbell, Richard L., Adaptive Array with Bin-aural Processor, Proceedings of the IEEEAntennas and Propagation Society Interna-tional Symposium, Philadelphia, PA, Jun1986, pp 953-956.

    Rick Campbell, KK7B, Binaural Presentationof SSB and CW Signals Received on a Pair ofAntennas,Proceedings of the 18th AnnualConference of the Central States VHF Soci-ety, Cedar Rapids, IA, Jul 1984, pp 27-33.

    Rick Campbell taught himself code and theoryand passed the Novice test as a young teen. Hisearly interest in radio has profoundly influencedhis career. He has been a US Navy Radioman,studied surface physics at Bell Labs in the 70s,and designed direct-conversion image-reject sat-ellite navigation receivers in the early 80s. From1983 through 1996, he was a faculty member inElectrical Engineering at Michigan Technologi-cal University. During the early 90s, he held asummer appointment at the US Department ofCommerce Institute for TelecommunicationsScience in Boulder, Colorado. In 1996, he leftacademia to join the advanced receiver develop-ment group at TriQuint Semiconductor inHillsboro, Oregon. In addition to designing andbuilding receivers, Rick also enjoys windsurfing,playing the violin and raising a family.

    You can contact Rick at 4105 NW Carlton Ct,Portland, OR 97229; [email protected]

    Figure 5The prototype binaural receiversVFO. The LO output is +10 dBm. This simpleVFO works exceptionally well, but must becompletely shielded for good D-C receiverperformance. A receiver with an open PC-board VFO will work better if the variableoscillator is not running on the received fre-quency. As noted elsewhere, the kit versionof the receiver uses a different VFO.