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Using TXAudio class to send IQ samples to Flex-6500 to transmit

NoelNoel Member

We've been working on establishing an interface between GNU Radio and a Flex-6500 radio where ideally GNU Radio would send IQ samples to the Flex-6500 to transmit. We've found a file called TXAudio Stream written by Flex Radio (https://github.com/cjam/FlexlibMono/blob/caa5c3c94212b725bceeac705ad3dbc51718f8c1/src/FlexLib/TXAudi...) where it seems that we can pipe samples into a TXAudio stream object to be sent to the Flex-6500 for transmitting. After looking at this file,https://community.flexradio.com/flexradio/topics/new/add_details?post_flow=true&topic%5Bsubject%5D=Using+TXAudio+class+to+send+IQ+samples+to+Flex-6500+to+transmit we have some questions:

- The class formats the audio as a stream of floats into a VITA-49 packet. Once this stream is sent, how does the Flex utilize it? Does it send it as is or does it perform some additional processing on the samples?

-  Could this class be used to send IQ samples instead of audio samples? If so, what additional changes would be required? We haven't seen anyone try to send IQ samples to a flex radio for transmission. Are there are any specific hardware limitations preventing this? Does the Flex-6500 even allow external IQ samples to be sent to it for transmission?

- Our final question is regarding this line of code, of which a screenshot is attached : _txDataEndPoint = new IPEndPoint(_radio.IP, 4991); It seems that 4991 represents a specific port number.  If we wanted to transmit IQ samples instead of audio samples, would a different port number be required?


Noel Teku


  • Doug - K3TZRDoug - K3TZR Member
    edited October 2018

    The Tx Audio stream is for sending audio from something external to the Flex Radio. The Radio's client (SmartSDR) has a button which, when toggled on, causes the radio to use the audio from this stream as the transmit audio (e.g. for a voice keyer). The radio mutes this source of audio if the microphone attached to the radio is activated.

    There is another type of stream, a DAX IQ stream that sends IQ samples from the radio to something external.

    There is a "helper" application called SmartDAX which is normally run with SmartSDR to control the various streams.

    I'm not aware of any ability to send IQ samples to the radio for transmission.

    A client for the Flex radio maintains a TCP connection for command and control usage to/from the radio, a UDP "connection" to receive streams of data (e.g. audio and/or IQ) and a a UDP "connection" to the radio on port 4991 to send a Tx Audio Stream to the radio.

    All of this is covered in the SmartSDR User's guide which can be downloaded from here:


    I hope that helps.

    73's Doug

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