50 (FET) Field Effect Transistor Projects - Battery Portable

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The output of the BFO or CO may be taken to the intermediatefrequency circuit of the receiver, as shown later. Alternatively, thebeat frequency or carrier oscillator can operate at the frequencyof the band being tuned. If so, no actual connection at all is necessaryto the receiver, as the wanted signal and oscillator signalare both fed into the receiver aerial circuit.This method is convenient for the low frequency amateurbands, especially 1.8-2.0MHz and 3.5-3.8MHz. It also has someadvantage where the receiver tuning control is of a type whichcannot easily provide critical tuning, as the latter will now dependon the signal frequency SSB/CW resolver.The circuit in Figure 27 will operate at a fundamental frequencyof approximately 1.75-2.0MHz, or 3.5-4.0MHz. The former rangeis suitable for both 160m and 80m, as the second harmonic ofthe 160m range will provide resolution on the 80m band. However,the 3.5-4.0MHz coverage is more suitable when 80m aloneis wanted, or some reception on perhaps 7MHz or 14MHz, withharmonics.
For the lower frequency range, C1 is 2<strong>50</strong>pF and VC1 is 75pF.L1 has fifty-seven turns in all, tapped at twelve turns from thegrounded end. The winding is of 32swg enamelled wire, on a 7/16th in or 11mm diameter former, with adjustable core. Turns areside by side. To cover the higher frequency range, L1 has thirtyturns, tapped at 6 turns, with wire and former as described. C1and VC1 are as shown.Stabilisation of the oscillator can be omitted when the currentis to be drawn from a separate battery, but becomes necessary ifthe circuit is operated from the same battery as the receiver. Otherwisefluctuations of supply voltage, especially at other than lowloudspeaker volume, will cause frequency modulation of the oscillator.Construction of the resolver should be in a metal case, withrigid mounting of components. A reduction drive is necessary forVC1.As the output from the oscillator passes into the receiver aerialcircuit, and is amplified with other signals, very loose couplingmust be used. It may be found adequate merely to place theresolver unit near the receiver aerial lead. If more coupling thanthis proves necessary, a lead a few inches long can be takenfrom the tap on L1, out of the screening box, and near to theaerial lead. The, degree of coupling is not too critical. But if this istoo great, signals will be swamped by the oscillator carrier. Alternatively,very loose coupling will give too low an input to the receiver,so that strong SSB or CW cannot be resolved.To operate the unit, tune in the wanted SSB or CW signal withthe receiver. Final tuning is now done with the resolver control, atthe point where the oscillator signal is heard to beat or mix withthe transmission tuned in. With CW, tuning is not too critical, asadjustments around the transmission frequency will merely alterthe audio pitch. But for good reception of SSB, tuning is quitecritical, as the resolver carrier should replace the carrier whichwas suppressed before transmission as correctly as possible.
Page 3 and 4: INTRODUCTIONField effect transistor
Page 5: type of FET is thus very useful whe
Page 8 and 9: Type No.BaseMaximumRatingsOther Inf
Page 10 and 11: Thus, over this range, a change of
Page 12 and 13: When building VHF units of this and
Page 14 and 15: FM BoosterFor long distance recepti
Page 16 and 17: y tapping the drain down L3. The su
Page 18 and 19: Range 3, 1.67-5.3MHz, or 580 to 194
Page 20 and 21: A metal cabinet about 6 x 4 x 4 in
Page 22 and 23: It the receiver has a signal streng
Page 24 and 25: Ham Band PreselectorAn amplifier or
Page 26: In view of the number of turns requ
Page 30 and 31: Layout should allow very short conn
Page 33 and 34: eak through. More care in finding a
Page 35: for each range is as shown below, w
Page 39 and 40: Any audio or general purpose FET ca
Page 41 and 42: Calibration of its scale can be by
Page 43 and 44: tion, VC1 tunes the inductor to res
Page 45 and 46: Should the field strength meter be
Page 47 and 48: here. The upper frequency limit at
Page 49 and 50: Coupling from the marker to the rec
Page 51: Coupling to the receiver can be by
Page 55 and 56: A control knob is necessary on VC1,
Page 57 and 58: Two inputs are required to the FET.
Page 60: much higher level, than that from a
Page 63 and 64: nals, the box or case must be of pl
Page 66 and 67: Values for Figure 33R1 1k C1 22uF 1
Page 68 and 69: Preamplifier for PhonesFigure 35 is
Page 70 and 71: The input socket, connected to C1,
Page 72 and 73: The “Radio” socket is suitable
Page 75: Audio power from the drain develops
Page 78 and 79: Yet another top cut control is show
Page 80 and 81: MISCELLANEOUS CIRCUITSThe miscellan
Page 82: 0.001 = 8000, so R1 is 8k. (Note th
Page 85: type intended for this purpose, and
Page 89 and 90: of the circuit, and 2nd, 4th, 6th
Page 92 and 93: Components for Figure 47C1 4.7nF si
Page 94 and 95: so that it can be swept about near
Page 96 and 97: The following will prove of aid to
Page 98 and 99: given, a deflection of somewhat ove
Page 100: BABANI PRESS BP 3950 (FET) Field Ef

50 (FET) Field Effect Transistor Projects - Battery Portable

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