Iiw

Fig. 3. Mixer stage.

FROM OSCILLATOR, 2965 TO 3165 M Hi

FROM OSCILLATOR, 2965 TO 3165 M Hi

Figr 4. First osc/Hator.

on L2 also works, but the single turn coil L3 is easier to adjust, so it was used in the final circuit.

The transistor used is of course our "Universal" one, the Motorola HHP 55 which is turning out to he a real low noise one, as well as universal. The emitter bias is temporarily adjustable, with a limit resistor R3 as well as a pot of IK, Base bias is supplied with the usual 10K and 2K resistors and isolated from L3 by C2. The collector is tapped onto L4, which is tuned by 04. L5 couples the amplified rf out to the next stage or to a receiver if you are using this unit as a preamp. Here are the results:

A. The collector tap has little or no influence on the amount of feedback causing oscillation. It does have an effect on bandwidth and tuning and thus a little on image suppression, but not much on gain. It is not critical.

B. The base tap, or size of L3 and its coupling to L2 has a very large effect on the feedback, A one turn loop with adjustable coupling to L2 around the cold end seems the best. With two turns for L3 oscillation occurs when L2 and L4 are tuned to the same frequency. With one turn none took place, and there was still plenty of gain. The present, or breadboard, L2 is 17 turns air-wound, 14mm OD, 6 turns per cm; however this is not yet padded for bandspread on the dial for 2 MHz.

Two types of tests were run on this rf stage, the first as a preamp in front of my lab receiver. This was really amazing- With

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