Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1997-11-26
2001-07-31
Hunter, Daniel (Department: 2684)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S314000, C455S316000, C455S076000, C331S017000, C333S013000
Reexamination Certificate
active
06269241
ABSTRACT:
BACKGROUND OF THE INVENTION
A dilemma exists in present day communications. As a result of the increased usage of cellular phones, there is a large amount of interference in bands around 900 MHz, that was not there previously. Consequently, many communications devices that used to work fine, before the advent of cellular phones are nonfunctional due to the added noise. Standard high frequency filters do not have the selectivity to filter out enough of this new noise to remedy the problem. Crystal filters have the selectivity to remedy the problem but operate at a much lower frequency.
The standard approach to filtering uses filters of the type available from TXRX, 8625 Industrial Parkway, Angola, N.Y., 14006, in their sales brochure, titled Multicouplers, Duplexers, Cavity Filters, 30 MHz to 960 MHz. Their Vari-Notch® and Series-Notch® filters are covered by U.S. Pat. Nos. 4,186,359 and 4,206,428. However, the filters of this brochure are inadequate for eliminating the noise from cellular phones. Those working in this area are baffled as to how to overcome the above mentioned dilemma.
Down converting a signal, filtering it and then up converting it and inputting it into a speaker was disclosed by U.S. Pat. No. 2,608,648. However, the input and output signal are typically different from each other in this invention.
Transponders at times have their input and output frequencies equal to one another. Heterodyning is a known technique used in some repeaters, transponders, carrier recovery systems, and phase stabilizing circuits. Some patents have issued having their input and output frequencies equal and/or that use heterodyning. The present inventor is aware of these U.S. Pat. Nos. 3,019,296, 3,946,293, 4,306,404, 4,743,843, and 4,972,346. U.S. Pat. No. 4,972,346 is of much significance to the present invention. The repeater of U.S. Pat. No. 4,783,843 is concerned with eliminating dead zones in the cellular phone bands. Thus, this repeater is set up to transpond two adjacent bands. The transponder U.S. Pat. No. 4,972,346 is concerned with eliminating the “singing” phenomenon. These problems are not the concerns of the present invention. U.S. Pat. No. 4,792,346 also as a prefilter/amplifier unit and a filter/amplifier unit after heterodyning in prior art
FIG. 2
, while U.S. Pat. No. 4,783,843 also has a filter before and after heterodyning. However, these patents do not discuss the purpose and the details of the filters and amplifiers before and after the heterodyning part of the circuit. These patents are for devices that are designed to connect to a known pair of antennas. The present inventor was the first to recognize the need for a device that could be inserted between a pre-existing antenna and receiver so that they can continue to operate with the additional noise from cellular phones. Furthermore, these heterodyning units all use a local oscillator of a fixed frequency, making them useful only in one frequency band.
SUMMARY OF THE INVENTION
The object of this invention is to provide a modular active filter that can be inserted between the antenna and a filter of a pre-existing unit, so that it can still function normally, without noise from cellular phones. This unit needs to be modular and needs to be able to work well with a large variety of antenna and receiver pairs, of different impedances, to be useful.
To accomplish this, a heterodyning unit is used with a prefilter/amplifier unit and a post-filter/amplifier unit. After down converting the signal, while heterodyning, the signal is put through at least one crystal filter to filter out the noise introduced by cellular phones. To make sure that the unit works well with a wide variety of antenna-receiver pairs, the resonant frequency of the filters of the pre and post amplifier/filter units is set to the center frequency that the antenna and receiver are designed to handle. In this way, only one type of unit needs to be manufactured for each frequency band. An example of such an operating frequency might be 900 MHz.
The method of using this invention involves the following steps: (1) install or adjust the resonant frequency of the filters of the pre and post amplifier/filter units to the desired frequency of operation for the antenna-receiver pair (2) disconnect the antenna from the receiver and (3) connect the antenna to the input end and the receiver to the output end of the modular active filter.
This invention has two types of embodiments. In one type embodiment the local oscillator produces only one fixed frequency. In the second and preferred type of embodiment, the oscillator has a connector that can except input from a laptop computer, for example. A simple key pad might or any means for a user to generate a set of signals corresponding to the desired set of frequencies can also be substituted for the laptop computer. This user generated input is then used to determine the output frequency of the oscillator.
REFERENCES:
patent: 4205284 (1980-05-01), Bouchou et al.
patent: 4647871 (1987-03-01), Turner, Jr. et al.
patent: 4783843 (1988-11-01), Leff et al.
patent: 4903297 (1990-02-01), Rist et al.
patent: 4941200 (1990-07-01), Leslie et al.
patent: 4972346 (1990-11-01), Kawano et al.
patent: 5416422 (1995-05-01), Dildine
patent: 5678218 (1997-10-01), Daikoku
AeroComm, Inc.
Gantt Alan T
Hunter Daniel
Quarles & Brady LLP
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