Make your own free website on


How to change the frequency band for VCO-circuit

The President George PLL-Circuit
The VCO generate 36.760MHz to 39.450MHz.
The transmit/receiver frequency is fVCO - 10.695MHz.

The President George VCO-Circuit
The VCO-frequency depends on a lot of component around D424 Varicap Diode.
By changing C452 the VCO will operated in a new frequency band. It is necessary to adjust L409 to get a proper operation.

By changing C452 to 33pF the VCO will operate 2 MHz upp, and changing C452 to 62pF the VCO will operate 2MHz down from the ordinary frequency band.
By re-tune FL401 Band Pass Filter and make a new TRANSMITTER PORTION and RECEIVER PORTION it is possible to get a new operating frequency band.
Remember to change the value of C4 and re-tune L2, see Receiver modification.

Location of C452
Click to enlarge