34 <strong>September</strong> <strong>2000</strong> Figure 1
Figure 1—Schematic of the OCR II circuit.Unless otherwise specified, resistors are1/4-W, 5%-tolerance carbon-compositionor metal-film units. RS part numbers inparentheses are RadioShack. Othersuppliers include Digi-Key Corp, 701Brooks Ave S, Thief River Falls, MN56701-0677; tel 800-344-4539, 218-681-6674, fax 218-681-3380; http://www.digikey.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. Also, see Notes 3 and 4.Equivalent parts can be substituted; n.c.indicates no connection.BT1—9 VBT2—9 to 12 V; see text.C1, C9—365 pF air-dielectric variableC6, C7—330 pF, 5% NP0; see text.C8—68 pF, 5% NP0; see text.C24, C27, C34—10 µF, 16 V electrolyticC23, C26—22 µF, 16 V electrolyticC29, C30—1 µF, 16 V electrolyticC31—220 µF, 16 V electrolyticD1—MV104 varactorJ1—Spring-action terminal strip(RS 274-315)J2—Three-conductor phone jack(RS 274-249)L1—Approx. 4.5 µH, 28 turns #24enameled wire on a T-68-2 coreL2—0.64 mH variable coil TokoRMC-2A6597HM (Digi-Key TK1302)Q1-Q4—2N3819, MPF102 (RS 276-2035)Q5—2N3904, 2N2222R1—1-kΩ, linear-taper pot (RS 271-1715)R6—10-kΩ, linear-taper, 10-turn panelmountpot; see text.R13—20-kΩ, linear-taper, PC-board mountpot; see text.R14—5-kΩ, linear-taper, panel-mount pot;see text.R24—10-kΩ audio-taper pot (RS 271-1721)S1—DPDT (RS 275-614)T1—Pri: 2 turns #26 enameled wire; sec:35 turns #26 enameled wire on T-68-2coreT2—Pri: 10 turns #26 enameled wire; sec:25 turns #26 enameled wire onT-50-43 coreT3, T4, T5—0.64 mH variable coil, TokoRMC-502182NO (Digi-Key TK1305)U1—NE/SA602 double-balanced mixerand oscillatorU2—HCPL4562 optoisolator (Newark#HPCL-4562)U3—LM78L05 5 V, 100 mA positivevoltage regulatorU4—LM386-4 audio amplifierMisc: PC board (see Note 3); two-inchdiameter vernier dial, 1 /4-inch shaft(Philmore #S50); 9-V battery snapconnectors (RS 270-234); 9-V batteryholders (RS 270-326); enclosure;hardwareclad perfboard, or “ugly” (“dead-bug”) constructionon a bare copper PC board. Theonly critical area is the SA602 oscillatorcircuit. NP0 (C0G) capacitors are used hereto enhance frequency stability. Use short,direct leads in this area. Make the circuitas mechanically robust as possible to helpensure stability. The hardware used for an-tenna connector J1 and switch S1 may bewhatever you prefer. You can fashion anenclosure from PC board, aluminum or usea manufactured enclosure. A fully closedcase is not required for good operation.Several prototype OCR receivers built asopen-frame units perform very well overreasonably constant temperature ranges.One of the more useful and interestingfeatures of the OCR design is the REGEN-ERATION control. This not only controls theamount of detector oscillation, but also controlsthe detector Q, which sets its bandwidth.With careful adjustment, bandwidthsof a few tens of Hertz are achievable justbefore the detector starts to oscillate. Totake advantage of this control, the pot usedfor regeneration control must have a fairlygood resolution. Although a multiturn potcould be used here, I took a morecost-effective approach. A board-mounted20-kΩ pot (R13) is used to preset R14, a5-kΩ front-panel-mounted pot, for regenerationcontrol. R13 is adjusted so that regenerationstarts with R14 at about 75% ofits maximum range. Used this way, R14gives very good control over the regeneration.This scheme works well because theoscillator frequency is fixed, and the regenerationpoint is quite constant. Because thetotal current used by the LED in U2 is onlyabout 400 µA, the change in battery voltagerelated to battery aging is very slow andtherefore, only infrequent R13 readjustmentis required.Checkout and OperationWhen you finish circuit assembly, carefullycheck your work for wiring errors andcold or missing solder joints. Verify that thecomponents have been installed correctlybefore applying power. Note that BT1, usedfor the regeneration circuit, should be aThe OCR II can bebuilt to use eitherwire antennas ortuned loop antennas.You can add theability to use eitherantenna by adding aDPDT switch to selectthe preselector circuit(used with therandom-length wire)or the loop antenna.9-V battery. This reduces noise in the detector.BT2 may be a 9-V battery for headphoneoperation or a 12-V battery for loudspeakeroperation.Once all has been checked, plug yourheadphones into J2 (phones with an impedanceof 16 Ω or greater give the best results)and apply power to the receiver. Theheadphones used should be of good quality.With the VOLUME control (R24) set atabout midrange, advance the REGENERA-TION control (R14) to about 75% of itsrange. Adjust the REGEN PRESET potentiometerR13 until you hear a gentle but distinctincrease in background noise. Thisindicates that U2 is oscillating and all iswell with the OCR detector circuit.Set the detector frequency by listeningfor the 455-kHz signal from U2 in a general-coveragereceiver. Adjust L2 to set theoperating frequency of U2. Alternatively,a frequency counter can be used to set thefrequency. (Many inexpensive digitalmultimeters now have frequency countersusable to 10-MHz.) To measure the frequencyof U2, connect the frequencycounter to pin 5 of U2. Although the signallevel is lower at pin 5 than at L2, measuringat this point avoids incorrect readingscaused by the probe loading the tank circuit.(Similarly, the converter-oscillator frequencycan be measured at pin 7 of U1; thisis discussed later.) As the detector frequencyis adjusted, the regeneration controlsmay have to be retouched to keep U2oscillating. It is not critical that U2’s oscillatorfrequency be set to exactly 455 kHzbecause there are no narrow filters used inthe receiver. It is only necessary that all theIF transformers be within adjustment rangeof each other.Verify that the mixer oscillator is operatingover the correct range by listening for<strong>September</strong> <strong>2000</strong> 35
- Page 6 and 7: September 2000 Volume 84 Number 9C
- Page 11 and 12: THE AMERICAN RADIORELAY LEAGUE INCT
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THE WORLD ABOVE 50 MHZInto the 21st
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AMATEUR SATELLITESA “Hot” After
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Christopher R.Gonyea, KB1AZKGoshen,
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75, 50 AND 25 YEARS AGOSeptember 19
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2000 ARRL RTTYRoundup ResultsBy Dan
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RA4CTR 14,674 253 58 ARA6AR 12,042
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Olli’s 2,100,744-point effort dem
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Puerto RicoWP4LNY 150,912 440 131 A
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K7RI868,140 3446 126 B CK7CAR 530,4
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