Measuring phase shift from cable length
Posted: Sun May 02, 2021 2:38 pm
Hi,
I'm trying to measure the phase shift that a carrier acquires when propagating through a length of cable. I have the bladeRF x40. I simply connect a 1 m sma cable from the TX port to the RX port. I'm using a Matlab script to configure the bladeRF using cli commands. My Tx samples are just ones, so that I just transmit a tone at the carrier frequency at 900 MHz. Then I expect to be able to obtain the phase acquired from propagation through the cable just by atan(imag(rx_sig)/real(rx_sig)). But when I try this, the measured phase is not consistent. It seems to be random between different measurements. Is there some fundamental reason why this won't work? Or am I just not implementing it incorrectly? I don't get why the phase measurement is not repeatable.
I should be able to use this phase measurement along with the permittivity of the cable I'm using, to back out the length of the cable (modulo the wavelength).
I'm trying to measure the phase shift that a carrier acquires when propagating through a length of cable. I have the bladeRF x40. I simply connect a 1 m sma cable from the TX port to the RX port. I'm using a Matlab script to configure the bladeRF using cli commands. My Tx samples are just ones, so that I just transmit a tone at the carrier frequency at 900 MHz. Then I expect to be able to obtain the phase acquired from propagation through the cable just by atan(imag(rx_sig)/real(rx_sig)). But when I try this, the measured phase is not consistent. It seems to be random between different measurements. Is there some fundamental reason why this won't work? Or am I just not implementing it incorrectly? I don't get why the phase measurement is not repeatable.
I should be able to use this phase measurement along with the permittivity of the cable I'm using, to back out the length of the cable (modulo the wavelength).