This version is outdated by a newer approved version.
This version (01 Feb 2019 18:21) is a draft.
Approvals: 0/1The Previously approved version (01 Feb 2019 02:47) is available.
This version (01 Feb 2019 18:21) is a draft.Approvals: 0/1The Previously approved version (01 Feb 2019 02:47) is available.
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Table of Contents
ADALM-PLUTO Transmit
Transmit Architecture
The AD9363 transmit chain is based on Direct Conversion techniques.
Some things to think about:
- The Tx LO is always the same amplitude, to get the best Signal to LO ratio, run the DACs as close to full scale as you can, and then turn up/down the output attenuation to vary the output signal strength. (Don't just decrease the input to the DAC). Full scale into the DAC is 12 bits and to supply a full scale signal using HDL provided by ADI will actually require a 16 bit signal to be provided, where the lower 4 LSBs are removed. See the AXI_AD9361 documentation for more details on these interfaces.
Transmit Performance
Details on the performance can be found in the performance section.
While there are many aspects of transmit performance, the two most common are:
- Output Power (how far can I transmit)
- Output fidelity (how accurate is the transmission)
For the ADALM-PLUTO, the both the output power and output accuracy are both frequency dependent.
Transmit Power
Most modern spectrum analyzers allow the measurement of the power within a frequency range, called the channel bandwidth. The displayed result comes from the computation:
Where is the power in the channel,
is the specified bandwidth (also known as the channel bandwidth),
is the equivalent noise bandwidth of the resolution bandwidth (RBW) used,
is the number of data points in the summation,
is the sample of the power in measurement
in dB units (if pi is in dBm,
is in milliwatts).
and
are the end-points for the index i within the channel bandwidth, thus
.1)
For this test an LTE10 signal was transmitted at various LO frequencies, and the power in the 9 MHz channel was measured and recorded:
This differs from the a continuous sine wave (CW) at various LOs, were the LO was swept from 70 MHz to 6 GHz. This is not measuring power in the channel, just peak transmit power (the spectrum analyzer was set up to do a peak hold). The two graphs show the difference between the Tx attenuation settings. The default setting of -10dB ensures that the analog output stages are running completely in the linear range, and will not saturate or come close to the 1PdB point. It is also safe at this setting to loop the Tx directly into the Rx with a SMA cable. Do not set the TX attenuation to anything less than -10dB and loop the Tx (output) signal into the Rx (input) connector.
The random peaks in the -10 dB attenuation settings are (I think) random noise caused by the Tx calibrations when the LO changes by more than 100 MHz.
As expected the wider LTE10 channel measurements have more power in it than a narrow CW signal.
Transmit Fidelity
This is a the output of the Keysight 89600 VSA software, which is used to measure signal demodulation and complete vector signal analysis. In this case, we generate an LTE 10 (10MHz wide channel), and transmit it out the Tx port of the ADALM-PLUTO, and capture it on the PXA N9030A Signal Analyzer. We can measure the RF offset (frequency error = 50Hz), and how accurate the 64-QAM constellation is created (an EVM of -46dB, or less than 0.5% RMS error) - which is pretty good. We can also see the output power (average peak output for the 10MHz channel is -45dBm/Hz).
By changing the LO frequency, output power, output attenuation, these results will change.
This is power out the SMA, not the antenna. Any antenna (including the one provided in the kit) may provide additional filtering (change the shape), as well as gain/attenuation
We need to re-do the tests in an RF chamber, to make sure there is no external noise.
university/tools/pluto/users/transmit.1549041677.txt.gz · Last modified: 01 Feb 2019 18:21 by Travis Collins