This 23cm converter was built to a design from QST. The Local oscillator is at 1280 MHz injected into the radial cavity 120 degrees away from the antenna and mixer diode, also at 120 degrees to each other.
The cavity is tuned with a large brass tuning screw.
The IF at 16-18 MHz is for connection into the HF receiver. The IF pre-amplifier is mounted on the side of the cavity and has a peaking capacitor for the part of the band in use.
The local oscillator consists of a third overtone 40 MHz crystal with transistor multipliers to 320 MHz. A 1N914 diode in a half wave strip-line cavity then performs the final multiplication to 1280 MHz. This is contained in the box below the cavity.
Performance was good when compared to other converters in the late 1960s. This is thought to have been due to the high Q of the cavity providing a degree of image rejection despite the low IF used.
The converter has remained untouched for the last 30+ years.