1. The following block diagram shows, in simplified form, the major building blocks
of a typical Tunable IF communication receiver used in amateur radio stations from
the 1960s onwards and capable of multi-
3. The various functional blocks shown above may be designed and assembled individually
from own designs or kits that are available from commercial suppliers. Consideration
must be given to the design of modules that may require to be bi-
The main receiver is shown above to the right and the crystal controlled converter to the left. The receiver will cover a single tuning range which may be an amateur band or not and the converter will cover as many ranges as is required. During the late 50s to the early 70s this was a well used technique used iin multiband HF and VHF transceivers. However, in the late 70s this receiver technique on the HF bands was replaced by designs using synthesised local oscillators and usually a single frequency conversion to the IF containing the main selectivity block in order to improve the dynamic range. However, local oscillator noise in the synthesiser restricted the overall dynamic range that could be obtained. See 2 below.
Much improved mixer and filter design from the 90s onwards means that the tunable
IF is still an option for good receiver performance without the use of synthesiser
techniques and their attendant noise problems. The H-
2. The following block diagram shows a dual conversion communication receiver with synthesised local oscillators. The second IF is optional but does provide a mechanism for providing significant gain at a lower frequency to the mode filters with a minimal risk of instability.
For continuous coverage receivers the first IF needs to be outside the receiver tuning
range and is frequently in the 40 -
However, for amateur band only applications a first IF of 9Mhz is popular as crystal filters are available commercially and may also be made by home constructors.