Local oscillator frequency sweep for ad9361 Transciever

Please see here: https://wiki.analog.com/resources/tools-software/linux-drivers/iio-transceiver/ad9361#local_oscillator_control_lo

Also page 23 here: https://www.gnuradio.org/grcon/grcon18/presentations/PlutoSDR/8-Michael_Hennerich.pdf

I'm pretty sure you can't use Verilog to sweep over this range. 

Controlling the RF PLL is a quite lookup and compute intensive task.

-Michael

Hey mhennerich !

1) If I understand the option as you pointed at page 23 then I have to write a C code for sweeping the RX LO? right?

2)If I am correct then Kindly guide me if there is any helpful material available available on the forum

2) Kindly you suggest  a suitable compiler for the code to run on the board.  

Regards!

You need to update the: 

out_altvoltage0_RX_LO_frequency, out_altvoltage1_TX_LO_frequency

sysfs attrinutes, how you do that it doesn't matter. You can write a shell script,
and write them directly. You can use iio_attr utility which can by the way generate example c code: 

https://wiki.analog.com/resources/tools-software/linux-software/libiio/iio_attr

You can do things in python, etc.

TANZI7702 said:

2) Kindly you suggest  a suitable compiler for the code to run on the board.

You didn't mention which board...

-Michael

Thanx mhennerich! Its ad9361-z7035 . 

mhennerich said:

You didn't mention which board..

regards!

If you use our SD card image there is already a ARM GCC compiler installed.

hey mhennerich , As you suggested I have written the following code to sweep the LO frequency. 

#include <unistd.h>
#include <iio.h>
#include <stdio.h>
#include <stddef.h>

#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <signal.h>
#include <stdio.h>
#include <errno.h>

int main(void) {
// Connect to IIO context
struct iio_context *ctx = iio_create_local_context();
if (!ctx) {
perror("Unable to create IIO context");
return -1;
}

// Open AD9361 device
struct iio_device *dev = iio_context_find_device(ctx, "ad9361-phy");
if (!dev) {
perror("Unable to find AD9361 device");
iio_context_destroy(ctx);
return -1;
}

// Get the LO frequency attribute
struct iio_channel *lo_channel = iio_device_find_channel(dev, "altvoltage0", true);
if (!lo_channel) {
perror("Unable to find LO frequency channel");
iio_context_destroy(ctx);
return -1;
}

// Define frequency range and step size
// long start_frequency = 2400000000; // 2.4 GHz
// long end_frequency = 2425000000; // 2.5 GHz
// long step_frequency = 10000000; // GHz step
long long s_frequency = 2400000000LL + (50000000.0/2.0);
printf("Start frequency %lld Hz",s_frequency);
long long e_frequency = 2500000000LL - (50000000.0/2.0);
printf("Ending frequency %lld Hz", e_frequency);
// Sweep frequencies
for (s_frequency; s_frequency <= e_frequency; s_frequency += 10000000LL) {
// printf("Setting LO frequency to %lld Hz\n", s_frequency);

// Set LO frequency
iio_channel_attr_write_longlong(lo_channel, "frequency", s_frequency);

iio_context_destroy(ctx);
return -1;
}

// Get the LO frequency attribute
struct iio_channel *lo_channel = iio_device_find_channel(dev, "altvoltage0", true);
if (!lo_channel) {
perror("Unable to find LO frequency channel");
iio_context_destroy(ctx);
return -1;
}

// Define frequency range and step size
// long start_frequency = 2400000000; // 2.4 GHz
// long end_frequency = 2425000000; // 2.5 GHz
// long step_frequency = 10000000; // GHz step
long long s_frequency = 2400000000LL; // + (50000000.0/2.0);
printf("Start frequency %lld Hz",s_frequency);
long long e_frequency = 2500000000LL ; //- (50000000.0/2.0);
printf("Ending frequency %lld Hz", e_frequency);
// Sweep frequencies
for (s_frequency; s_frequency <= e_frequency; s_frequency += 10000000LL) {
// printf("Setting LO frequency to %lld Hz\n", s_frequency);

// Set LO frequency
iio_channel_attr_write_longlong(lo_channel, "frequency", s_frequency);
printf("Setting LO frequency to %lld Hz\n", s_frequency );
// Optionally, add a delay between frequency changes
usleep(1000000); // 100ms delay
}

// Cleanup

iio_channel_disable(lo_channel);

iio_context_destroy(ctx);

return 0;
}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

it does sweeps the frequency, but the problem is when I check it on the iio- oscilloscope, there is a frequency mis-match. The frequencies that I I am controlling are different from the ones shown on the spectrum analyzer. You can easily compare the LO values in the left with the peak value in the right side. Though the cursor moves as I sweep the frequency, but the values are not synchronizing. Kindy guide me why it is happening and how can I fix it?

This doesn't surprise me.

OSC fetches the currently LO frequency once it starts, and then later the plot is notified by a callback in case the LO or sampling frequency changes.

https://github.com/analogdevicesinc/iio-oscilloscope/blob/master/plugins/fmcomms2.c#L317

If you control things on the back of OSC using an external application, osc plot doesn't get notified.

Hey mhennerich ,I wanted to visualize the LO sweep on oscilloscope to authenticate it. What If I dont use oscillocope? Can you suggest me any other way to sweep the RX_LO which can assure me either RX LO is really sweeping or not?

Well, you can sweep the TX and observe it on a spectrum analyzer.

Alternatively, use python to control and visualize.

-Michael 

Hey mhennerich , I am sweeping the tx  from 400Mhz to 1100 Mhz. But I can only visualize the sweep on spectrum analyzer with the delay (sleep(1) ) of 1 second or greater. However, I want to lock the PLL as fast as possible. Moreover the default PLL lock time for ad9361 varries from 45 micro seconds to 60 micro seconds. Now tell me with this fast lock time how can I visualize it on the spectrum analyzer. 

my spectrum analyzer (FSH8-2) allows to visualize as fast signals as that of 80ms.