I'm interested in whether it would be possible to use the ADALM-PLUTO time-of-arrival localization. This requires a very stable clock. I wonder whether it will be possible to feed in an external reference clock? In the revision-B schematics, it looks like there is no connector or jumper to switch from the built-in 40MHz oscillator to an external clock.
Also, if I do feed the clock from an external source (even if this involves removing the 40MHz oscillator), how difficult will it be to switch from 40MHz to 10Mhz? I see that the AD9363 does support 10MHz clocks, but will it is reasonably easy to configure the firmware for this clock frequency?
Thanks, Sivan Toledo, Tel-Aviv University
Yes - you should be able to lift off the current oscillator, and use an external clock. There is a hole in the PCB specifically for this purpose. All you need to do is lift C123, and put a 1.3V p-p clock into that node.
Since we have a 1.8V oscillator, we are using C123/C124 as an AC divider to get things down to 1.3V p-p. The internal capacitance of the pin means we don't actually need to stuff C124 to achieve this.
The Input Frequency Range for the reference clock is from 10 - 80 MHz. That is spec'ed in the datasheet. After that, it should be a simple matter of updating the device tree to tell the Linux driver you are using something different than 40MHz.
as a suggestion since is not so easy to solder and external clock input instead the C123 maybe should be great in rev. C to add some kind of test point (or even a connector) to feed the external clock with a jumper to select the input source.
This is the typical solution in most fpga development kits but maybe you have a better solution.
External clock for ADALM-PLUTO SDR
AD recommends/necessary steps are:
- remove TCXO 40.0 MHz and
- provide the external synchronisation via C123
It would be very helpful if AD could foresee on the PCB a Land Pattern for the installation of Ultra Miniature Coaxial Connector, UMCC, Part No. 128-0711-201 from Emerson Network Power (or install this connector):
Therefore, the external synchronisation can be easily provided via UMCC:
See https://coherent-receiver.com/pluto-sdr for more details.
Thanks in advance.
Thanks for the write-up.
We will take this into consideration if/when we release a new rev of the PCB.
All you have to change is this line in the device tree:
linux/zynq-pluto-sdr.dtsi at master · analogdevicesinc/linux · GitHub
However you need to rebuild the plutosdr-fw image to apply the change.
Have a look also here -
Coherent Transceivers based on ADALM-PLUTO SDR | RTL-SDR Multi-Channel Coherent Receivers