trying to use hilbert transf. to envelope my ultrasound RF data, but not working

[northPIG87]

Hi all,

As searching through the forum, I've come across a program "Echo detector" that uses hilbert transform to envelope a simulated sinewave signal. I've then modified the source of the signal within the vi, and inputted my own signal: one line of radio-frequency (RF) data from an ultrasound probe with sampling frequency 50MHz. The RF file is a simple binary data file in unsigned 16bit. There are 512 data points in this file so total of 1024 bytes. 

When I try to use the hilbert transform on this sets of data, I do not seem to be able to get the envelope of the RF data.

Am I missing something? because it works well for the simulated data, which is no more than bunch of numbers in an array, which is the same in my case.  

>< thank you all for your help!

i've attached the echo detector VI with a slight modification so that you can switch between the original and my set of RF data..which is also attached

[Marco_Brauner]

Hi, just from a qualitative point of view, I think your signal is too noisy to get a envelope by doing hilbert-transform.

I cannot prove you mathematically, but that´s what I found when successively adding noise to a amplitude-modulated cosine and

calculating the envelope by hilbert-transform of the imaginary part, like in the example.

So I think it is only possible with a high enough SNR.

M. Brauner NIG

[northPIG87]

Hi Hans, THanks for the reply.

So I've attempted to filter the signal first as I've realized in ultrasound, RF filtering is required prior to hilbert transform (evenlope detection). I've implemented a simple bandpass filter. The signal looks cleaner but after hilbert transform it is still not detecting the envelope. Is it still simply due to the low SNR? 

I've attached the Vi i'm using trying to get the envelope detection working with a dat file of a line of RF raw data. 

Thank you all for your help!

[Marco_Brauner]

Hi, try out my VI and you´ll see that below a certain amount of noise you are getting relatively proper envelopes.

When the signal is too noisy or the carrier-signal´s freq is too low, the envelopes are becoming worse.

Marco