Using External Local Oscillators¶

Some AIR-T models provide external LO inputs (transmit and receive) to allow an external LO source to be used with the device.

Please check the Product Guide in the AIR-T section for your model to determine if this mode of operation is supported and for the specific power requirements for the input signal. As an example, the AIR7201 model can accept an external LO input signal between 0 and +6 dBm for LO frequencies up to a maximum of 4 GHz. In addition, for the AIR7201, the input LO frequency must be double that of the desired LO frequency, e.g., 8 GHz input creates a 4 GHz LO. This is summarized in the following table:

Receive External Local Oscillator¶

Connect an external synthesizer to the RLO (receive) connector at twice the desired LO frequency. Next, the configure SoapySDR device. The External LO is enabled via the SoapySDR Device instantiation argument rx_lo_src="external". For example, modify the Receiving Samples with Python tutorial by doing the following replacement:

Replace:

sdr = SoapySDR.Device(dict(driver="SoapyAIRT"))       # Create AIR-T instance

sdr = SoapySDR.Device(dict(driver="SoapyAIRT", rx_lo_src="external"))

It is important that the frequency value used in sdr.setFrequency(SOAPY_SDR_RX, 0, freq) is the desired LO frequency, not necessarily the input frequency.

Transmit External Local Oscillator¶

Connect an external synthesizer to the TLO (transmit) connector. Next, configure the SoapySDR device. Just as in receiving, the External LO for transmitting is enabled via the SoapySDR Device instantiation argument: tx_lo_src="external". For example, modify the Transmitting on the AIR-T tutorial by doing the following replacement in the transmit_tone function as follows:

Replace:

sdr = SoapySDR.Device()  # Create AIR-T instance

sdr = SoapySDR.Device(dict(tx_lo_src="external"))