DWM1001C fluctuating measured distance

Hello everyone, I am using DWM1001C and starting up anchor and tag using the ss_twr_init and ss_twr_resp. However, the distance being measured between the transceiver and receiver varies by a large amount. Currently, they are 0.3175 m apart physically but the distance measured are ranging from 0.375229 m to 0.562843 m. I’m aware that the antenna delay needs to be calibrated but are these fluctuations normal?

Antenna delay will give you a constant offset not a fluctuating number.

Is there anything between the units? How are they orientated? Are they laying flat on a desk?

If the boards are standing up with a clear line of sight between the antennas you should get a stable measurement. What you are seeing implies that some of the time the direct signal isn’t getting through and they are seeing a reflection instead.

Hi Andy, thank you for the reply. The boards are standing up, not facing each other but facing the same direction. There are no obstruction between them and they are standing up on a flat table.

I checked to see if the table is forming multipaths by changing only the distance from the ground by 23 inches but the distance read is still fluctuating.

I changed the distance between them to 5.01 m and the measured distance is now between 5.309484 m to 5.497098 m which is better in terms of not much fluctuation.

Is there a minimum distance that the distance will be too inaccurate to rely on?

20 cm of variation still seems high, it should be under 10 cm. Can you try rotating them to face each other?

I’ve never seen a measurement noise issue at short ranges, our system (admittedly using different hardware & firmware) will give stable readings at 10 cm even if we crank the power up 10 dB over the FCC limits. We do get a constant offset error at very sort ranges that out normal compensation system doesn’t quite dial out but the noise is still stable.

When I changed the distance to 5.01 m, I did make them face each other.

Keep in mind, I haven’t messed with the antenna delay calibration yet but is this variation in the distance measured still expected?

Hey there.
I had a problem kinda like that before and the antenna delay was the most importante parameter to “solve” that.
I used a MDEK1001 kit so the antenna delay comes calibrated from factory but the error stil greater then 10 cm. So i did get new value for antenna delay and then my distances start the become more desired.
What i mean is that the devices comes calibrated with a positive error and the sum of both devices cause that greated distance error/difference.
There are another aspects to take care about distances but antenna delay is one i’ve got better results in my first approach.
Try to see if the values of delays on communications used are lower too.