SINGLE WIDE BAND VCO FOR RX AND TX
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-16
In transceiver radios with high-side injection mixers utilizing a single local oscillator (LO) for receiving (RX) and transmitting (TX), to switch from RX to TX it is necessary to reduce the LO frequency. This can be accomplished by either increasing the inductance or capacitance of the tank circuit. Also, for FM operation it is necessary to provide means, generally a variable capacitance, to shift the frequency. The frequency deviation for FM is 5KHz, which requires a very small capacitance change, while the frequency shift from RX to TX may be more than 45MHz. At present, switch- ing from RX to TX is accomplished by increasing the inductance and a variable capacitor is used for modulation.