Reexamination Certificate
1999-05-04
2001-10-02
Maung, Nay (Department: 2681)
C455S272000, C455S269000, C455S277100
Reexamination Certificate
active
06296565
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to diversity antenna switching systems. In particular, this invention relates to a low cost, diversity antenna switching system for use with high fidelity audio equipment.
BACKGROUND OF THE INVENTION
Diversity receiving systems and diversity antennas are well known in the communications art. In general, diversity antenna systems are used to accommodate the RF signal fading and multi-path signal propagation anomalies that are common at VHF and UHF frequencies. Signal fading and multi-path signals can adversely effect reception of a radio frequency's signal and, by selectively choosing one of two or more spatially separated antennas that pick up a signal, fading and multi-path effects can be reduced. Multiple antennas are routinely used with cellular telephones and automobile radios.
Multiple antennas are now also used with wireless microphone systems, which include a remote, low-power portable transmitter, the signals of which are received and demodulated by a receiver. As a wireless microphone is moved about a room, multi-path signals can adversely affect the demodulated audio output from the receiver because multi-path signals will produce phase anomalies in the reception process that sound like popping noise or may even cause complete audio loss. Accordingly, diversity antenna systems are now employed in such wireless microphone systems to overcome the adverse effects of multi-path and signal fading.
At least one problem with a diversity antenna system is switching the appropriate antenna to the receiver in such a way so as to seamlessly couple the receiver to the proper antenna. Prior art systems exist for selecting one, or a combination of two or more antennas to be coupled to a radio receiver. Some of these prior art systems are disclosed in U.S. Pat. Nos. 5,777,693 to Kishigoami, et al. for a “diversity receiving apparatus for a mobile unit;” U.S. Pat. No. 5,517,686 to Kennedy, et al. for a “diversity Receiver for FM Stereo Utilizing a Pilot Tone Multiple For Phase Alignment of Received Signals;” U.S. Pat. No. 5,548,836 to Taromaru for a “Diversity Receiver;” U.S. Pat. No. 5,465,411 to Koike for a “Diversity Receiver With Switching Noise Reduction;” U.S. Pat. No. 4,29,955 to Gehr, et al. for a “Diversity Reception System;” U.S. Pat. No. 5,742,896 to Bose, et al. for a “Diversity Reception With Selector Switching at Super Audible Rate;” U.S. Pat. No. 5,697,083 to Sano for a “Diversity Receiver;” and see U.S. Pat. No. 5,603,107 to Gottfried, et al. for a “Switching System For Diversity Antenna FM Receiver.”
When high fidelity audio reproduction is required in a small size package and at the lowest possible cost, prior art diversity antenna switching system are too complex, too large or too expensive. Prior art low cost, switching systems also suffer from audio switch noise spikes that they produce in the receiver when they perform a hard instantaneous switch over from one antenna to another. A low cost, compact, method, and apparatus for selecting one or more antennas in such a way that audio fidelity reproduction is maximized would be an improvement over the prior art .
SUMMARY OF THE INVENTION
Using PIN diodes as variable RF signal attenuators, in series between each of the antennas of a diversity antenna system and the radio receiver input in a wireless microphone system, the strongest signal received from a transmitter can be seamlessly selected at the receiver without producing noise spikes caused by phase differences between the antennas. The PIN diode will conduct radio frequency energy when biased in the forward direction. By gradually biasing a PIN diode to conduct in a forward direction, its attenuation of a RF signal can be gradually increased and decreased. In a diversity antenna system, a PIN diode connected in series between the antenna and the receiver input, can be gradually forward biased, thereby gradually reducing the attenuation of RF signals passing through the diode from the antenna to the input. Simultaneously, another PIN diode connected in series with another antenna and coupled to the receiver input, can be gradually reversed biased so as to gradually attenuate signal from the other antenna.
By gradually modulating the bias current of PIN diodes, they can be used to progressively attenuate and de-attenuate signals from two or more diversity antennas that arc coupled to a common summing node that is coupled to the input of the radio receiver. Signals received by one antenna can be seamlessly combined with signals from another antenna so as to avoid sudden phase shifts that can produce unacceptable audio output noise spikes.
PIN diodes are small, inexpensive and easily controlled to modulate their RF attenuation level.
REFERENCES:
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patent: 5603107 (1997-02-01), Gottfried et al.
patent: 5697075 (1997-12-01), Kim
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patent: 5697083 (1997-12-01), Sano
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Article dated Aug. 11, 1999 from Lectrosonics, Wireless Guide obtained from http://www.lectro.com/wg/wgdiv.htm regarding Diversity Reception.
Advertisement dated Aug. 11, 1999 purportedly from “Samson” obtained from http://www.samsontech.con/wireless/press/coniv-press.html regarding the Concert IV System.
Advertisement dated Aug. 11, 1999 from Samson from the Internet at http://www.samsontech.com/wireless/press/series-one-press. html regarding the UHF Series One.
Article dated Aug. 11, 1999 from the Internet at http://www.telex.com/PSE/WebPages . . . regarding Professional Audio Technical Information How Wireless Work; Diversity Reception.
Article “Wireless Microphone Systems: Description,” publication date unknown, author unknown.
Kenkel Mark A.
Reihl Edgar C.
Banner & Witcoff , Ltd.
Maung Nay
Shure Incorporated
Trinh Sonny
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