Modified Bandpass Set

This set is based on designs by Al Klase with input from Steve Bringhurst. The coupling coil is key to this approach. The detector side of the coupling coil may be reduced to 5 or 6 turns to increase selectivity. If you have a long antenna, try putting a 200 pf capacitor in series with the antenna just before C1. This will minimize loading of the antenna tank (parallel coil/capacitor) circuit. Al prefers series tuned matching for the antenna circuit.

In the KE4ID version the antenna coil was tapped. Since the dual cap used in that version had a ceramic insulated shaft, the tapped coil approach worked fine. Without an insulated shaft, the two rotors are connected electrically, and the tapped coil approach won't work, unless two separate (not ganged) capacitors are used.

Front view of the KE4ID version of the Modified Bandpass Receiver

Notice the ARC-5 cap and 100k : 100 ohm audio transformer

>

Note ceramic insulated cap for the trap and the dual section antenna cap.

Schematic for the set click for large view.