Continuous tuning control particularly adapted for use in variable frequency receivers and generators

DETAILED DESCRIPTION OF DRAWINGS In order to gain a clear understanding of the nature of the invention, there is shown a block diagram of a typical commercially available radio receiver which employs a synthesizer to effectuate coarse tuning.
Essentially, the receiver shown in FIG.
1 is a digital type of superhetrodyne using a phase locked loop synthesizer to effectuate step tuning in 5 KHz intervals and includes additional means for continuous fine tuning within each 5 KHz range.
It is this means for continuous tuning which emcompasses an embodiment of the invention to be described.
Before proceeding with an analysis of the operation of the receiver and the advantages of the invention, it is of course, understood that the ability to continuously tune over the 5 KHz interval to be described is a desirable feature in a signal generator as well as a radio receiver and it is well known that techniques for generating such signals, whether used for the local oscillator frequency of a receiver or used as a standard for test purposes as in a signal generator, present similar problems.
Particularly, the ability to tune over a 5 KHz interval in a radio receiver or over a relatively small interval is extremely desirable in modern commercial receivers.
As indicated, such receivers employ a frequency synthesizer to generate the local oscillator signal which may be varied in discrete steps by means of suitable switches.
The receiver includes a continuous tuning means to enable the user to tune the receiver over a particular range defined by one of the steps.
There are, of course, many examples of highly stable switchable step tuned receivers.
See, for example, U.
S.
Pat.
No.
2,501,591 entitled MULTIBAND SUPERHETRODYNE RADIO RECEIVER HAVING A PUSHBUTTON SELECTOR issued on Mar.
21, 1950 to H.
M.
Bach, the Inventor herein.
See also U.
S.
Pat.
No.
2,529,443 entitled MULTIBAND SUPERHETRODYNE RADIO RECEIVER HAVING A PUSHBUTTON STATION SELECTOR issued on Nov.
7, 1950 to H.
M.
Bach.
Other patents such as U.
S