VFO/VFO Amplifier Pictures

The center compartment holds the VFO. A relay is tie wrapped to the VFO toroid, which is connected to a magnetically coupled Huff & Puff Stabilizer. The relay and toroid are covered with candle wax to provide mechanical stability.

The board in the right compartment are two MOSFET VFO amplifiers. The circuit boards for the VFO and MOSFET amplifiers were taken from "surface mount" prototypes made during the development of the Electroluminescent Receiver.


The panel mount variable capacitor at the top right is adjusted from the front panel to make adjustments to the VFO on the fly. This capacitor was used as an antenna trimmer in the stock HQ140X.

The VFO only covers about 80 kHz, so this capacitor makes roaming through the band a lot easier. It was also used to set the VFO to work with the 40 meter band, when a 40 meter bandpass filter was installed in the receiver.

The large electrolytic capacitor at the lower right and the smaller .01's nearby are used for power supply filtering, very important for this part of the receiver.

The relay (tie wrapped to the VFO toroid) was a small square one, with all the switching parts removed. It fit perfectly on the T68-6 toroid, and is wired to the Huff & Puff stabilizer with 75 ohm miniature coax cable.

The cable was also enclosed in wax to keep it from moving around and causing frequency shifts. An RF choke is directly below the cable, feeding 12 Volts to the VFO, and it was also covered with a thick coat of wax. Experiments have shown that temperature changes in the RF choke affects VFO stability.

The VFO is run at 5 Volts, supplied by a regulator (7805) that is located below the large electrolytic capacitor. See image at the top of this page.

MOSFET Amplifiers

These MOSFET amplifiers come directly from the Electroluminescent Receiver. Input on the left, output on the right.

Power is applied through an RF choke, with .01 caps to ground on each side of the RF choke.

Output is approximately +7dBm.

2N5109 Final VFO Amplifier

This amplifier provides the necessary output for a diode mixer. Output is somewhere between 1/2 watt to 1 watt to provide the drive for a high level mixer.

The 2N5109 amplifier is the same as the post-mixer amp in the Progressive Communications Receiver.

A 3db and a 6db Pi-network resistive pad can be seen at the bottom middle of the image (bent over close to the ground plane). These were used to fine tune the drive level to the mixers that were installed for testing.

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Last Update: 12-18-2002
Web Author: David White, WN5Y