A UHF/microwave converter

Down conversion is used to allow reception of ultra high frequency (UHF) and microwave signals (which is over 300 MHz). The UHF or microwave input is mixed with the LO to provide an output which falls within the tuning range of a shortwave VHF receiver. A block diagram of a down converter for UHF/microwave reception is shown in the figure given below.

This converter has an output which covers a huge band of frequencies.  Actually, a single frequency allocation at UHF or microwave may be larger than the entire frequency range of a shortwave receiver.  An example is a UHF converter designed to cover 1.000 GHz to 1.100 GHz. This is a span of 100 MHz, over 3 times the whole range of a shortwave radio.

To receive 1.000 to 1.100 GHz by using a down converter and a shortwave receiver, LO frequency should be switchable. Assume that you have a communications receiver which tunes in 1-MHz bands. You may choose one of these bands, say 7.000 to 8.000 MHz and use a keypad to choose LO frequencies from 0.993 GHz to 1.092 GHz. This will generate a difference-frequency output at 7.000 to 8.000 MHz for 100 segments, each of them is MHz wide, in desired band of reception.If you want to hear segment 1.023 to 1.024 GHz, you set LO at 1.016 MHz. This generates an output range from 1023 − 1016 = 7 MHz to 1024 − 1016 = 8 MHz.