L1 and VC1 can be selected from a wide range of values, tosecure the coverage required. It is convenient to fit the Denco(Clacton) “Red” oscillator coils, of valve type. With these, pin 8 is taken to drain (S1) and pin 9 to C1. Pin 1 goes to S2 for all coils except Range 1, when pin 7 is used. The appropriate ground pin for each range is as shown below, which indicates the bands over which these coils can be used, with a capacitance swing of approximately 20-350pF for VC1.
Range 1. ( 5 ) 380 - 1600kHz.
Range 2. ( 2 ) 0.8 - 3.5MHz.
Range 3. ( 3) 2 - 8.5MHz.
Range 4. ( 4 ) 6 - 22MHz.
Range 5. ( 6) 15 - 45MHz.
If other coils are used, allowance has to be made for the omissionof the usual padders and trimmers, as well as for the difference in receiver aerial and oscillator frequencies.
S1/S2 can have as many ways as bands required. However, the higher frequency coils need short connections, and coils must be reasonably separated from each other. Numerous general
purpose and RF type FETs will be found suitable. The presence of oscillation throughout each band can be checked with a meter in one battery lead - current should change if VC1 is shorted. The drain feedback winding must be correctly phased to obtain oscillation.
VR1 is an output attenuator. Construction should be in a metal cabinet, with a reasonably large scale for VC1. Calibration can be by the methods described later.
The signal produced by this generator is unmodulated, or silent. Unmodulated RF is used for tuning sharp crystal filters, and can be used for alignment of receivers which have a tuning meter or indicator, or where a meter is clipped to the AVC circuit to show the effect of adjustments. For other purposes, it is necessary that an audio tone is present with the carrier or RF signal.
