Implementation

 

 

 


 

Implementation

Notes

  1. Analog filter is always enabled.
  2. When a manual gain is selected the gain mode is switched to manual as well.
  3. The SDR cannot tune outside the range allocated to the chip - AD9363 or AD9364.
  4. There's a hardware 'hack' which makes the AD9363 think it's an AD9364 which has a greated tuning range.
  5. The digital filter is supported, it's impressive!
  6. Multiple devices are supported, the serial number is used when connecting.

 

This is a very fine SDR, excellent value.

 

Antennas

Although the API returns a list of available antenna choices for both RX and TX, only one antenna from the lists can be applied. When connecting to a pluto, the RX antenna is set to A_BALANCED and the TX antenna is set to A. If a future revision of the Pluto hardware supports more than one antenna then this logic will be updated.

Attributes

The hardware attributes of the development unit:

hw_model                 = Analog Devices PlutoSDR Rev.B (Z7010-AD9363)
hw_model_variant         = 0
hw_serial                = 104473dc59930019edff1100d8cd2918d7
fw_version               = v0.29
ad9361-phy,xo_correction = 39999965
ad9361-phy,model         = ad9363a
local,kernel             = 4.9.0-10475-g2398d50
usb,idVendor             = 0456
usb,idProduct            = b673
usb,release              = 2.0
usb,vendor               = Analog Devices Inc.
usb,product              = PlutoSDR (ADALM-PLUTO)
usb,serial               = 104473dc59930019edff1100d8cd2918d7

Bandwidths

Receive

From the device driver notes the minimum bandwidth is 2.083 MSPS unless FIR Decimation / Interpolation is set, so in this software the lowest bandwidth is 2.1 MHz, the maximum sustained throughput without packet loss is 6MHz.

Transmit

The sum of the receive and transmit bandwidths cannot exceed 6MHz, so transmit is only enabled for bandwidths of 3 MHz and lower as the Pluto implementation runs in full duplex (simultaneous receive and transmit).

Gain Control Modes

This text is from Analog Devices [link].

Manual: In MGC mode, the BBP controls the gain index pointer(s). In its simplest form, the BBP evaluates the digital signal level at the I/O port and then adjusts the gain appropriately. The BBP can control manual gain in one of two ways. The default method uses SPI writes (writing in_voltage[0,1]_hardwaregain) the total gain in dB. This results in different gain indices depending on the gain table loaded. Alternatively, the BBP can pulse the Control Input pins to move the gain indices.

Slow attack: Slow Attack Mode is intended for slowly changing signals such as those found in some FDD applications such as WCDMA and FDD LTE. The Slow Attack AGC uses a 2nd order control loop with hysteresis that changes the gain in order to keep the average signal power within a programmable window.

Hybrid: The AGC hybrid mode is the same as the slow AGC mode with the exception that the gain update counter is not used. Instead, gain updates occur when the BBP pulls the CTRL_IN2 signal high. The “hybrid” term arises because the BBP has taken some control of the algorithm away from the AD9361 so gain control is no longer completely automatic.

Fast attack: Fast Attack Mode is intended for waveforms that “burst” on and off, such as those found in TDD applications or GSM/EDGE FDD applications. The AGC responds very quickly to overloads at the start of a burst so that the AGC can settle to an optimum gain index by the time the data portion of the signal arrives.

Spur, Image reduction

The spur you may see in the center of the display is automatically reduced as much as possible, similarly image reduction caused by IQ imblanace is enabled in the AD9363 chip.

Transmit

The radio runs in full duplex (receiver runs while transmitting). This is required for transponders such as Es'Hail 2 (a geostationary satellite). There is a menu option RX Mute which is used to disable the waterfall and audio while in transmit mode.

Delay

If you monitor your transmission with the Pluto you will experience a delay; this is due to the buffer sizes used in the Libiio API. The buffer sizes will be customisable in a future version of this software.

Drive

For maximum drive make sure the band-specific Master Gain levels are set to 100 [Link].

  • In the Transmit DSP press ••• to display the Transmit Options.
  • In the Transmit Options select Audio In, Gains.
  • Select the current band.
  • Set Drive to 100%.
  • Set Gain and Proc (processing) to suit your voice.

GPIO

Pluto has four general purpose output (GPO) pins. Direct support of these pins is not possible via the Libiio library.

Monitoring

Due to the design of the AD9364/AD9363, if both, the TX and RX Local Oscillators (LO) are set to the same frequency or very close to each other  the TX LO may leak into the RX path. Monitoring your own signal with Pluto in full duplex mode is not recommended; use a second receiver instead.

If you do monitor with Pluto in full duplex then turn the RX Gain to 0dB to avoid overloading the receiver stages.

Spur

There is a spur approximately 50dB below peak output at the transmit frequency. This is generated by the AD9363 / AD9364 chip in Pluto, the cause and possible mitigation are being investigated. It is probably DC leakage from an internal mixer [link].

USB Port

To achieve the maximum sample rate of 6 MSPS (6 MHz bandwidth) a good, powered USB port must be used. USB3 is not necessarily better than USB2; so if there are breaks in the received data try a different USB port. Pluto's USB is USB 2.0 High-Speed.

Pluto has a second USB connector for additional power - don't be afraid to use it!

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