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There are several factors which determine the rate at which data flows from one block to the next. However, many beginners assume that if, for example, a waveform source is set to a certain frequency, and a sample rate is set, then that output signal will be at that rate. But, as opposed to a hardware circuit, the signal is just data in a buffer. The following sections will illustrate this.
 
There are several factors which determine the rate at which data flows from one block to the next. However, many beginners assume that if, for example, a waveform source is set to a certain frequency, and a sample rate is set, then that output signal will be at that rate. But, as opposed to a hardware circuit, the signal is just data in a buffer. The following sections will illustrate this.
  
This discussion is based on the flowgraph of a RadioTeleTYpe (RTTY) receiver. It can be found at [https://github.com/duggabe/gr-RTTY-basics/blob/master/RTTY_rcv/RTTY_receive.grc]
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This discussion is based on the flowgraph of a RadioTeleTYpe (RTTY) receiver:
  
[[File:RTTY_rcv.png|960px]]
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[[File:RTTY_rcv.png|900px]]
  
 
Frequency shift keying (FSK) tones are input to the microphone jack of the computer which has a sample rate of 48khz. That data is fed to a Frequency Xlating FIR Filter which shifts the tones above and below the center frequency. It also decimates (divides) the sample rate by 50, producing an output sample rate of 960.
 
Frequency shift keying (FSK) tones are input to the microphone jack of the computer which has a sample rate of 48khz. That data is fed to a Frequency Xlating FIR Filter which shifts the tones above and below the center frequency. It also decimates (divides) the sample rate by 50, producing an output sample rate of 960.
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The output of the Quadrature Demod block has a sample rate of 960; the desired sample rate is 500. The Rational Resampler interpolates (multiplies) the sample rate by 500 and decimates (divides) it by 960 to produce an output sample rate of 500.
 
The output of the Quadrature Demod block has a sample rate of 960; the desired sample rate is 500. The Rational Resampler interpolates (multiplies) the sample rate by 500 and decimates (divides) it by 960 to produce an output sample rate of 500.
  
The 'Terminal Display Sink' is an Embedded Python Block which reads the input stream of 1's and 0's, synchronizes on the start bit, creates a Baudot character from the five data bits, converts Baudot to UTF-8, and outputs the characters to a ZMQ PUSH Message Sink.
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The 'Terminal Display Sink' is an Embedded Python Block which reads the input stream of 1's and 0's, synchronizes on the start bit, creates a Baudot character from the five data bits, converts Baudot to UTF-8, and displays the characters on the user terminal screen.
  
 
== Sink hardware example ==
 
== Sink hardware example ==

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