i see unwanted spikes or noise in the input

[mancane]

I am running a chirp signal, with start frequency 1KHz to 42KHz, with a sample rate of 500k and taking 35000 samples. The DAQ card is the 6070E . Im outputing the signal through the transducer and reading in the received signal with another transducer, in between them there is an obstacle, in this case a round wooden pole. The received signal has some undesirable spikes all over and tried, filtering but cant seem to solve the problem. Can I perhaps get some advice on how to get remove or block of them. I have attched my VI. 

[Henrik_Volkers]

A picture of the noise would be nice.

Are the transducers powered? Clean powersupply (tried batteries)?

Any noise sources near by (switched power supplies, energy saving lamps, ....)?

Chokes in the out- and input to the card sometimes help.

The median filter is an effective spike remover.

[mancane]

Thanks for the reply. I will try your suggestions. I do have a power supply for the opamp that im using to amplify the input signal. I have attched the pictures of the graphs maybe there is another explanation. Thanks

[Henrik_Volkers]

Better post png or jpg, a lot of peoples (me included) don't like to open .doc files from unknown sources.....

[mancane]

hi there i have attached jpeg pics. Also to add pic1 and 2 is when the sample rate is 500k and 35000 samples. But while trying on my side i changed the sample rate to 300000 and the 3000 samples and it seems the spikes have decreased(pic 3 and 4). Is the a possible explanation for that. Thanks 

[Henrik_Volkers · Accepted solution]

If your timescale is right, you have spikes about every 0.5ms , every ms a positive and a negativ. Looks like a highpass coupled 1kHz squarewave flying around... maybe catched by a groundloop or in your amplifier, bad signal cables, ...

Another source can be the DAQ card input itself. try a choke (ring core filter)  for that. Do you have a (best analog) scope somewhere to measure without the daq input? 

Can you power the amplifier with a batterie (or a really good DC source) for a test?

[mancane]

hi I will try that and also put the input signal through a bandpass filter and see what I get. Thanks

[mancane]

Hi thanks.Ｔｈｅ　ｓｐｉｋｅｓ　ｗｅｒｅ　ｂｅｉｎｇ　ｐｉｃｋｅｄ　ｕｐ　ｆｒｏｍ　ａｎ　ｏｓｃｉｌｌｏｓｃｏｐｅ　ｎｅａｒ　ｂｙ．　Ｔｈａｎｋｓ　ａ　ｌｏｔ！！