Magazine Peterborough New Hampshire

The carrier at 913 kHz, the upper sideband at 916 kHz, and lower sideband at 914 kHz. These signals are heterodyned with the second conversion oscillator in the second mixer stage, The second conversion oscillator is crvstal controlled at 1000 kHz and 830 kHz.

The selection of one of them is done by switch S-4, As the second if is tuned to 86 kHz, the 830 kHz oscillator would give upper sideband (916 kHz of first if) and the 1000 kHz oscillator would give lower sideband (914 kHz of the first if). In the frequency conversion process the carrier still remains at 85 kHz. It should be remembered that the above conversion holds good only for band 5 and 6, where the first conversion oscillator is lower than the incoming signal. The operation of USB and LSB switching will be just the reverse in the case of the lower bands 1 to 4. Here the first conversion oscillator is higher than the incoming signal. An effective selecting of the sidebands can be established by reducing the bandwidth of the 2nd if frequeue} . This can be accomplished by making use of tapped points in the 85 kHz if transformers and by pulling up the secondary coil for loose coupling.

The circuit diagram does not include the power supply for the receiver. A suitable power supply unit can be built externally and connected to the receive) as shown.

Construction

The construction of the complete receiver is divided into three modules, each being external!v wired and interconnected after tjiey are placed in the original chassis. The wiring of the original receiver was completely removed except for the avc packs on which only the avc feed was changed. For ease in wiring, the original chassis frame between the inverter unit and the if assembly was cut away. The first module consists of rf amplifiers and the first mixer. This stage of wiring is easy as there are only a few components. After wiling, this module can be put in its original place. Access to the tube base connection is possible through the front panel opening. The second module consists of the detectors, af ampliers, and first if (915 kHz) amplifier. The third module contains the second mixer, 86 kHz if and the S meter tube. Most of the components of this module are placed on circuit boards and mounted close to the respective tubes.

M any of the components of modules 2 and 3 are circuit-boarded and the arrangemen: of components does require some constructional experience. The frame between the coil pack and modules 2 and 3 will accommodate all the supply distribution among the modules. To insure better chassis continuity', a

metal braid interconnects the modules. The top view of the receiver does not show the 830 kHz crystal as the photo >vas taken prior to (he wiring of the crystal. The output transformer takes the original place in the

BC-348,

Aiter construction, the alignment procedure is normal. Care should be taken while aligning the 2nd if stage that it is exactly peaked for 86 kHz. as this would determine sideband selection.

I am sure this unit would equal most of the moderately priced receivers on the market- Of course, for many of our ham friends who can buy one for cash, it may sound a waste of time to build Ins own receiver? but this is not the case in India where almost everything in the shack must be home-brew,

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235 Montana ^re,

Santa Monica, Ca/z/. 90403

235 Montana ^re,

Santa Monica, Ca/z/. 90403

Ever been frustrated by a pyramid o! test gear and that inevitable octopus of tangled leads and power cords, while trying to align or trouble shoot your receiver. Or perhaps, like me, the minimal closet space of modern apartment dwelling has prevented you from harboring much in the way of test equipment. In either event, you can use a Gentrac.

Originally conceived as a cdo-air test set for receiver work, the Gentrac also possesses useful capabilities for transmitter and audio circuit testing in a single, transistorized package which can be used anywhere.

The Gentrac incorporates two individual units from which its name is derived:

1) A multi-purpose generator, furnishing the most needed signals for communications work

2) An rf/af signal tracer and output meter, Only two test leads are required; one for generator output and the other for tracer input, eliminating the usual cats cradle that confounds the more conventional set-up. Here is what the Gentrac has to offer:

Generator Specifications.

100 kHz and 1MHz calibrated markers up to 200 MHz Crystal controlled oscillator output in the range of 100 kHz to 30 MHz on fundamentals; up to 200 MHz on harmonics.

Audio sine and square waves over the voice frequency range of 250 to 2,500 Hz, Broadband "white" noise* Modulation of rf output by 250 to 2,500 Hz sine wave, or unmodulated. Generator output low impedance, and continuously variable over a 60 db range for all signals.

Tracer Specifications.

Input impedance: selectable 1 megohm or 10 kohm,

Input Sensitivity (gain): selectable 150 mV or 3 mV,

AF input: Direct, rf input; with external probe.

Output: Selectable to internal speaker and/or VU meter

Circuit Description—Generator.

A schematic of the generator is shown in Fig, 1# For convenience the circuit has been divided into six basic sections by dotted lines, and labeled Gl, G2, G3, G4, G5 and GO, being the individual Oscillator and output circuits as follows:

(G1 Marker Generator—Q1 is a dual controlled oscillator, selectable for 100 kHz and 1 MHz output. Capacitors C2 and C3 permit accurate frequency adjustment. Q2 is a bormonic amplifier for the 100 kHz output only, providing markers well up into the VHF range,

(G2) H.F. Generator.-Q3 and Q4 comprise an untuned crystal oscillator functioning over the range of 3 to 30 MHz, (G3) L.F. Generator,—Q5 is an untuned crystal oscillator functioning over the range of 100 kHz to 4 MHz. (G4) A.F. Generator.~Q7 is an RC coupled, phase-shift oscillator, with good quality sine-wave output, continuously variable over the 250 to 2,500 Hz range. This oscillator also drives Q8 and Q9, which comprise a square-wave amplifier, for providing square wave output, (G5) Noise Generator —Diode D2 is a conventional. noise generator, utilizing either a SN21 or 1N23. The diode current regulator resistor R6a, is a potentiometer section ganged to the output attenuator R6b, Thus, while the output attenuator is not used with the noise generator, the noise

G1 lOOkHz/IMHz GEN

lf xtal ose audio osc white noise

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