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Topic: VFO


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  Class E Transmitters - Two band VFO (80 and 160 meters)
The VFO produces a two phase output (2 outputs), making it well suited to supplying a signal to either single ended RF amplifiers, where only one of the outputs is used, or to balanced (push-pull or single ended push-pull) RF amplifiers where both outputs would be used.
Referring to the VFO Schematic, the circuit uses a Hartley oscillator operating between approximately 7 to 8 mHz.
The VFO relay should not be the only source of control for the high voltage supply, rather the relay should be in series with the coil of the high voltage power supply control relay(s) as ONE of the conditions for high voltage supply operation.
www.classeradio.com /vfo.htm   (915 words)

  
 VFO Circuit
This VFO is probably the most stable FET circuit out there, but I have found that the active device you use can make a big difference in the stability of the VFO.
A stable VFO is one of those homebrew projects that always seems to give the most trouble.
The vfo circuit is very easy to design for any frequency (see NE602 Front End) and uses fewer parts than the FET VFO.
www.pan-tex.net /usr/r/receivers/vfo.htm   (739 words)

  
  Electroluminescent Receiver - VFO
The relay on the left is activated by switching the bandpass filter to 20 meters, moving the VFO to 10.455 MHz.
In the pictures explaining the IR switching, a fl tube is seen at two places, one that goes across from the crystal filters to the middle of the VFO amps and one at the bottom of the 20 meter bandpass filter.
The IR receiver between the VFO amplifiers is a photo transistor and the one at the bottom of the VFO is a photo diode.
www.qsl.net /wn5y/elrvfo.htm   (1716 words)

  
 VFO Circuits
The C3 trim cap is used to set the VFO frequency to 10.455 MHz, along with C7.
C16 is one section of the original main tuning capacitor of the HQ-140-X. The VFO is placed in the metal box with the main tuning capacitor.
A good combination is the Variable MOSFET VFO amplifier followed by the 2N5109 (w/resistive pad) into a diode mixer.
www.pan-tex.net /usr/r/receivers/svfo.htm   (2971 words)

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