Telecommunications – Transmitter – Amplitude modulation
Reexamination Certificate
1999-01-15
2001-01-23
Vo, Nguyen (Department: 2745)
Telecommunications
Transmitter
Amplitude modulation
C455S203000
Reexamination Certificate
active
06178312
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to communication systems, and is particularly directed to a new and improved mechanism for automatically tuning the frequency synthesizer of a radio transceiver, such that its transmit and receive frequencies correspond to those of respectively different (upper band and lower band) filters to which the radio transceiver has been connected.
BACKGROUND OF THE INVENTION
Because the majority of users of electronic devices are technically unsophisticated, telecommunication service providers are continually seeking ways to make installation, set up and use of their equipment as simple as possible. In the course of setting up radio transceiver equipment at a respective end of a two way radio link, such as is diagrammatically illustrated in
FIG. 1
, for example, interference may be encountered. To avoid this interference or other reasons, the customer may be required to change the transmit and receive frequencies from one assigned plan to another in order to achieve satisfactory system operation. When this situation is encountered, the customer is customarily required to perform three tasks.
The first is to connect the radio's antenna
11
to the antenna port
13
of a diplexer
15
containing transmit and receiver filters for the radio
17
, proper.
The user is also required to connect the radio's transmitter and receiver ports
21
,
23
to filter ports
31
,
33
of the diplexer
15
, as specified on a frequency assignment plan for that customer's end of the link.
Finally, the user must tune the radio's frequency transmit and receiver synthesizers to the respective frequency bands of the diplexer filters, in order to conform with the customer's transmit and receive frequency assignment plan, such as that shown in FIG.
2
. In the frequency assignment example of
FIG. 2
, the radio
17
at a ‘west’ end of the radio link is to be configured to transmit within a first ‘lower’ frequency F
L
band
41
, and to receive within a second ‘upper’ F
H
frequency band
43
. Conversely, a radio at the ‘east’ end of the link is to transmit within the ‘upper’ frequency F
H
band
41
, and to receive within the ‘lower’ F
L
frequency band
43
.
While the first two steps involve the user only making physical connections between components, and are essentially foolproof, the third step requires the user to make a pair of parametric adjustments to set the operation of the radio, and often results in a set-up failure. This, in turn, leads to the customer calling the service provider and the need to inject service personnel into the process.
SUMMARY OF THE INVENTION
In accordance with the present invention, this problem is effectively obviated by incorporating a pair of relatively simple, complementary impedance coupling circuits into the diplexer's filter stages, and modifying the transceiver to include a logic level generator circuit, having a frequency band monitor node which indicates to which filter ports of the diplexer the customer has connected the radio's transmit and receive ports. The output of the logic level generator circuit is read by the transceiver's control processor to automatically tune the transmitter and receiver frequency synthesizers to the respective frequencies of the diplexer filters as connected by the customer.
For this purpose, the upper band filter stage of the diplexer includes a capacitive-coupling interface circuit that provides a first, low impedance path between an upper band filter port and the upper band filter stage's tuned cavity at the operative frequency band of the filter, while effectively blocking DC. The lower band filter stage includes an inductive-coupling interface circuit which, in addition to providing a low impedance connection between the lower band filter port and the tuned cavity of the lower band filter stage, provides a DC path to ground.
The logic level generator may comprise a pull-up resistor coupled between a high voltage reference terminal and a frequency band monitoring node that is ported to an input/output bus of the radio's control processor. The frequency band monitoring node is further coupled to a transceiver's (transmit or receive) port through a relatively low value coupling resistor or inductor, which forms a voltage divider with the pull-up resistor.
In operation, once the customer has connected the diplexer's filter ports to transmit and receive ports of the transceiver as specified in the radio's frequency assignment plan, the voltage reference circuit will provide either a relatively high voltage associated with the upper frequency band F
H
, or a relatively low voltage associated with the lower frequency band F
L
, depending upon how the user has wired up the equipment. If the transceiver port of interest has been connected to the diplexer's upper band filter port, the frequency band monitoring node will have the relatively high voltage level, since the low value resistor is terminated by a DC open circuit, as a result of being coupled to the DC-blocking, capacitive-coupling interface circuit of the upper band filter stage. Since the high voltage level is representative of the upper frequency band F
H
, the control processor will tune the transmitter's frequency synthesizer to the upper frequency band F
H
, and the receiver's frequency synthesizer to the lower frequency band F
L
.
On the other hand, if the transceiver's transmit port has been connected to the diplexer's lower band filter port, the frequency band monitoring node will be coupled through the low value resistor and the DC path through the inductive-coupling interface circuit of the lower frequency band filter stage to ground. Because the value of low value resistor is considerably smaller than that of the pull-up resistor, the frequency band monitoring node is effectively coupled to the low voltage level, and the control processor will tune the transmitter's frequency synthesizer to the lower frequency band F
L
, and the receiver's frequency synthesizer to the upper frequency band F
H
.
REFERENCES:
patent: 5481186 (1996-01-01), Heutmaker et al.
patent: 5781860 (1998-07-01), Lopponen et al.
Adtran Inc.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Mehrpour N.
Vo Nguyen
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