Simple Watt Phasing Type Ssb Exciter

pole double-throw switch in the output circuit of the cathode follower permits sideband selection.

A Filter-Type Exciter for 80 and 40 Meters

A simple SSB filter-type exciter employing the Collins mechanical filter illustrates many of the basic principles of sideband generation. Such an exciter is shown in figure 39. The exciter is designed for operation in the 80 or 40 meter phone bands and delivers sufficient output to drive a class ABi tetrode such as the 2E26, 807, or 6146. A conversion crystal may be employed, or a separate conversion v-f-o can be used as indicated on the schematic illustration.

The exciter employs five tubes, exclusive of power supply. They are: 6U8 low frequency oscillator and r-f phase inverter, 6BA6 i-f amplifier, 6BA7 high frequency mixer, 6AG7 linear amplifier, and 12AU7 speech amplifier and cathode follower. The heart of the exciter is the balanced modulator employing two 1N81 germanium diodes and the 455 kc., 3500-cycle bandwidth mechanical filter. The input and output circuits of the filter are resonated to 455 kc. by means of small padding capacitors.

A series-tuned Clapp oscillator covers the range of 452 kc. — 457 kc. permitting the carrier frequency to be adjusted to the "20 decibel" points on the response curve of the filter, as shown in figure 40. Proper r-f signal balance to the diode modulator may be obtained by adjustment of the padding capacitor in the cathode circuit of the triode section of the 6U8 r-f tube. Carrier balance is set by means of a 5 OK potentiometer placed across the balanced modulator.

One half of a 12AU7 serves as a speech amplifier delivering sufficient output from a high level crystal microphone to drive the second half of the tube as a low impedance cathode follower, which is coupled to the balanced modulator. The two 1N81 diodes act as an electronic switch, impressing a double sideband, suppressed-carrier signal upon the mechanical filter. By the proper choice of frequency of the beating oscillator, the unwanted sideband may be made to fall outside the pass-band of the mechanical filter. Thus a single sideband suppressed-carrier signal appears at the output of the filter. The 455 kc. SSB signal is amplified by a 6BA6 pentode stage, and is then converted to a frequency in the 80 meter or 40 meter band by a 6BA7 mixer stage. Either a crystal or an external v-f-o may be used for the mixing signal.

To reduce spurious signals, a double tuned

6ba6 Receiver Diy Ssb Circuit Diagram

Figure 39



Figure 39


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