Simultaneous signal detection for IFM receivers by transient detection
First Claim
1. In an instantaneous frequency measurement (IFM) receiver which has receiving means including a limiter, which in response to simultaneous signals produces heterodyne signals which absorb energy and therefore reduces the output for signals in a filter band, discriminator and detector circuits to provide sine and cosine signals, and logic circuits for processing the sine and consine signals to provide a frequency output in a digital format as a frequency measurement, the improvement comprising:
- transient detection means for digital detection of a simultaneous signal condition, comprising two analog-to-digital converters, first and second memories, and comparison means;
said converters having respective inputs coupled one to the sine line and the other to the cosine line of the receiver, and respective outputs providing the sine and cosine signals in digital form;
the converter outputs being coupled to address inputs of the first memory, which by table look up provides a digital output of the square root of the sum of the squares of the sine and cosine signals, and which used as the amplitude of a detector receiver signal;
the second memory having address inputs coupled to a given number of leads of said frequency output, the second memory having stored therein data for each frequency addressed data representing amplitude values at a lower level than the minimum amplitude at that frequency for a single signal condition;
the outputs of the first and second memories being connected to corresponding inputs of the comparison means, the comparison means having an output on which a comparison output signal is at a first level in response to the output of the first memory being less than the output of the second memory and otherwise being at a second level, the presence of simultaneous signals being flagged when the comparison output signal is at the first level.
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Abstract
The instantaneous frequency measurement (IFM) receiver is highly susceptible to erroneously reporting frequency if two or more signals are overlapped in time. This problem is extremely important when the receiver is presented with synchronized signals. A method is presented to detect simultaneous signals which overlap in the critical frequency encode strobe.
In essence, during the pulse overlap condition, a transient will occur on the video output lines of the receiver. These lines are monitored during the transient period and compared with predetermined values which are obtained from the single signal condition. If a transient is detected, a simultaneous signal detect flag is raised and this flag is sent to an associated processor. In this special design, the receiver will measure the frequency again at approximately 200 ns from the first measurement. The transient detection is also performed on the second measurement.
37 Citations
5 Claims
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1. In an instantaneous frequency measurement (IFM) receiver which has receiving means including a limiter, which in response to simultaneous signals produces heterodyne signals which absorb energy and therefore reduces the output for signals in a filter band, discriminator and detector circuits to provide sine and cosine signals, and logic circuits for processing the sine and consine signals to provide a frequency output in a digital format as a frequency measurement, the improvement comprising:
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transient detection means for digital detection of a simultaneous signal condition, comprising two analog-to-digital converters, first and second memories, and comparison means; said converters having respective inputs coupled one to the sine line and the other to the cosine line of the receiver, and respective outputs providing the sine and cosine signals in digital form; the converter outputs being coupled to address inputs of the first memory, which by table look up provides a digital output of the square root of the sum of the squares of the sine and cosine signals, and which used as the amplitude of a detector receiver signal; the second memory having address inputs coupled to a given number of leads of said frequency output, the second memory having stored therein data for each frequency addressed data representing amplitude values at a lower level than the minimum amplitude at that frequency for a single signal condition; the outputs of the first and second memories being connected to corresponding inputs of the comparison means, the comparison means having an output on which a comparison output signal is at a first level in response to the output of the first memory being less than the output of the second memory and otherwise being at a second level, the presence of simultaneous signals being flagged when the comparison output signal is at the first level. - View Dependent Claims (2, 3, 4, 5)
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Specification