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What (besides sw compatibility) is needed for SDR?

Posted: Mon Jul 15, 2019 2:37 am
by rgfuller

An SDR dongle seems to be a radio receiver with a USB interface to pass signals to SDR software. But clearly a USB interface is not enough, because many radios that have USB interfaces are not recognized by SDR software. What else is needed that cannot be provided by software alone?

For example, why can't a Yaesu 891 (which has a USB interface) be used with popular SDR software? Is it a matter of protocol support? What else is missing?


Re: What (besides sw compatibility) is needed for SDR?

Posted: Mon Jul 15, 2019 4:56 pm
by hotpaw2
USB hardware devices are allowed by the USB spec to have completely different profiles. Just because the connector looks the same does not mean that the profile supported is the same. A USB flash drive is quite different from a USB audiophile DAC. Different USB profiles. And you can only communicate with a device using it's built-in profile.

Some radios (probably your Yaesu) only support simple commands over a virtual serial port. Others can stream digital audio. Others can stream data. And a few, such as the RTL-SDR (SDRPlay, Airspy, LimeSDR, etc.), can stream SDR IQ data.

To use an older transceiver with certain kinds of digital-mode and SDR software, you can plug the audio and mic jacks into a PC sound card or sound card dongle for DSP. RigBlaster, SignaLink, sells commercial products for this purpose.

Re: What (besides sw compatibility) is needed for SDR?

Posted: Tue Jul 16, 2019 10:25 am
by rtlsdrblog
An SDR at it's very core is an analog to digital converter (ADC). So it needs this ADC hardware to be classed as an SDR.

Standard radios don't use ADCs, they use standard analogue components to process the radio signals into audio. They can be computer controlled, but the RF signal is never digitized.

An SDR gives the antenna signal to the ADC, which converts it into a digitized signal. That digitized signal is then processed in software, and demodulated/decoded into audio/data etc.