Convert power spectrum back to original waveform

Hi,
I have program my PXI 5610 to transmit a sine wave to my PXI 5600.
But when I use the 'ni5660 Read Averaged Power Spectrum VI' to read the signal, it comes out as a power spectrum.. So how can I convert this power spectrum back into my sine wave to show it on the graph.
I am new into this field, hopefully someone can help me out.
Thanks.
Jieyi
Attachments:
wiring.GIF ‏9 KB

Hello Jieyi,
When you read your signal as spectrum, you loose the phase data. You can still get your signal back but it would not have any information about the phase. I would suggest you acquire the time domain data. This is very simple since the driver can do everything for you.
The time domain data will be automatically converted to In Phase (I) and Quadrature Phase (Q) which are two components that changes the carrier. You can read more about IQ signals here.
Then, you can open the example called ni5660 Getting Started IQ.vi located under "\LabVIEW 8.x\examples\instr\ni5660" and look at this:
Finally, if you have modulation toolkit, you can open any modulation example to transmit a sinewave. These are located at:
"\LabVIEW 8.x\examples\Modulation\RFSG examples"
For example, AM:
Transmitter (Tx)
MT RFSG Generate AM.vi
Receiver (Rx)
MT ni5660 Demodulate AM.vi
These examples are ready to transmit any standard waveform including your sinewave.
Hope these information helps,
Message Edited by Yardov on 08-17-2007 06:50 PM
Gerardo O.
RF Systems Engineering
National Instruments
Attachments:
acquire time domain signals.JPG ‏46 KB

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Attachments:
accelero.vi ‏93 KB

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Check this out!
http://zone.ni.com/devzone/cda/epd/p/id/6388
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You can see a Video of it working here
http://www.ni.com/mcm/wind/
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Preston Johnson
Principal Sales Engineer
Condition Monitoring Systems
Vibration Analyst III - www.vibinst.org, www.mobiusinstitute.com
National Instruments
[email protected]
www.ni.com/mcm
www.ni.com/soundandvibration
www.ni.com/biganalogdata
512-683-5444

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Attachments:
Save Power Spectrum.vi ‏55 KB

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Attachments:
Power Spectrum.vi ‏19 KB

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Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
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Attachments:
Powerspectrum.vi ‏25 KB

Hi Jud,
why do you attach a BMP renamed to JPG? Please attach real JPGs or (even better because of lossless compression) use PNG format! There's a reason why BMPs aren't allowed as attachment...
I attached your pic converted to PNG. Do you spot the difference?
Message Edited by GerdW on 08-02-2008 03:40 PM
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
Error3.png ‏13 KB

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Corby_B
http://www.ni.com/support
Attachments:
Power Spectral Density.jpg ‏225 KB
WAV Power Spec.jpg ‏202 KB
Power Spectrum.jpg ‏142 KB

Converting a byte[] back to key problem

I CAN create a key and convert the key to a byte array, then convert the array to a string(base 64):
KeyGenerator generator = KeyGenerator.getInstance("DES");
generator.init(new SecureRandom());
key = generator.generateKey();
byte[] keyBytes = key.getEncoded;
BASE64Encoder encoder = new BASE64Encoder();
String randomKey = encoder.encode(keyBytes);
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BASE64Decoder decoder = new BASE64Decoder();
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Many thanks in advance guys!
Cheers!
Relisys
================ CODE FOLLOWS ======================
import java.io.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import com.sun.crypto.provider.SunJCE;
import sun.misc.*;
public class SecPrescrip {
public static void main(String[] args) throws Exception {
// Create Key.
Key key;
KeyGenerator generator = KeyGenerator.getInstance("DES");
generator.init(new SecureRandom());
key = generator.generateKey();
// Get a cipher object
Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
// Encrypt the input string:
cipher.init(Cipher.ENCRYPT_MODE, key);
String input = "Medicare Secure Prescription: 30 Tamazopan 200mg tablets. Dosage: 1 to be taken every 4 hours";
System.out.println("Stage 1: ENCRYPT PRESCRIPTION WITH A RANDOM DES KEY");
System.out.println("===================================================");
System.out.println(" - Input Plain Text: "+input);
System.out.println("");
byte[] stringBytes = input.getBytes("UTF8");
byte[] raw = cipher.doFinal(stringBytes);
BASE64Encoder encoder = new BASE64Encoder();
String ciphertext1 = encoder.encode(raw);
System.out.println(" - Cipher Text: "+ciphertext1);
System.out.println("");
byte[] keybytes = key.getEncoded();
String randomkey = encoder.encode(keybytes);
System.out.println(" - Random Prescription Key: "+randomkey);
System.out.println("");
System.out.println("ENCRYPTION SUCESSFULL");
System.out.println("");
System.out.println("");
System.out.println("Stage 2: ENCRYPT RANDOM KEY WITH PATIENT MEDICARE KEY");
System.out.println("=====================================================");
BASE64Decoder decoder = new BASE64Decoder();
String passphrase = "ABCD1234efghIJ56"; //Patient Medicare Key
System.out.println(" - Patient Medicare Key: "+passphrase);
System.out.println("");
System.out.println(" - Input Plain Text: "+randomkey);
String algorithm = "PBEWithMD5AndDES";
byte[] salt = new byte[8];
int iteration = 20;
KeySpec ks = new PBEKeySpec(passphrase.toCharArray());
SecretKeyFactory skf = SecretKeyFactory.getInstance(algorithm);
SecretKey key2 = skf.generateSecret(ks);
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MessageDigest md = MessageDigest.getInstance("MD5");
md.update(passphrase.getBytes());
md.update(input2);
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System.arraycopy(digest, 0, salt, 0, 8);
AlgorithmParameterSpec aps = new PBEParameterSpec(salt, iteration);
cipher = Cipher.getInstance(algorithm);
cipher.init(Cipher.ENCRYPT_MODE, key2, aps);
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String ciphertext2 = encoder.encode(outputFinalKey);
String saltString = encoder.encode(salt);
String encryptedCiphertext = saltString+ciphertext2;
System.out.println("");
System.out.println(" - Cipher Text (Final Prescription Key): "+ciphertext2);
System.out.println("");
System.out.println(" - Salt: "+saltString);
System.out.println("");
System.out.println(" - Full Encrypted Output: "+encryptedCiphertext);
System.out.println("");
System.out.println("ENCRYPTION SUCESSFULL");
System.out.println("");
System.out.println("");
System.out.println("Stage 3: DECRYPT PRESCRIPTION KEY USING PATIENT MEDICARE KEY");
System.out.println("============================================================");
//NOT CHANGED String passphrase = "ABCD1234efghIJ56";
System.out.println(" - Patient Medicare Key: "+passphrase);
System.out.println("");
System.out.println(" - Input Plain Text: "+ciphertext2);
algorithm = "PBEWithMD5AndDES";
salt = new byte[8];
iteration = 20;
ks = new PBEKeySpec(passphrase.toCharArray());
skf = SecretKeyFactory.getInstance(algorithm);
SecretKey key3 = skf.generateSecret(ks);
//Load in the input bytes as if they had been loaded from an sql database or the like
String saltIn = encryptedCiphertext.substring(0,12);
String ciphertext3 = encryptedCiphertext.substring(12,encryptedCiphertext.length());
byte[] saltArray = decoder.decodeBuffer(saltIn);
byte[] ciphertextarray = decoder.decodeBuffer(ciphertext3);
aps = new PBEParameterSpec(saltArray, iteration);
cipher = Cipher.getInstance(algorithm);
cipher.init(Cipher.DECRYPT_MODE, key3, aps);
byte[] outputKey2 = cipher.doFinal(ciphertextarray);
String plaintext2 = encoder.encode(outputKey2);
System.out.println(" - Plain Text (Random Generated Key): "+plaintext2);
System.out.println("");
System.out.println("");
System.out.println("ENCRYPTION SUCESSFULL");
System.out.println("");
System.out.println("");
System.out.println("Stage 4: DECRYPT PRESCRIPTION KEY USING PATIENT MEDICARE KEY");
System.out.println("============================================================");
// The decrypter string plaintext should be the same as the BASE64 Encoded representation of the random DES string
byte[] randomKeyFetched = decoder.decodeBuffer(plaintext2);
generator = KeyGenerator.getInstance("DES");
DESKeySpec keyspec = new DESKeySpec(randomKeyFetched);
* Stuck here! Once the key is reformed it will be complete!
}

You need to use a SecretKeyFactory to convert the byte array back to a SecretKey to use in decryption. Continuing your example:
SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
DESKeySpec desKeySpec = new DESKeySpec(loadedKeyBytes);
SecretKey sk = skf.generateSecret(desKeySpec);
Use sk in the call to the Cipher init() function. (Note that you don't call KeyGenerator to restore a key from its bytes.)
Incidently, if you're using ECB mode for encryption I don't think you need to worry about the Initialization Vector. However, if you're using CBC mode (which is the default DES mode for the default SunJCE provider), I believe you also have to make sure that the decryption system starts from the same Initialization Vector that was used for encryption. To deal with this, if 'cipher' is your encryption Cipher object, then you call
byte bytIV[] = cipher.getIV();
to get the 8-byte IV array. To decrypt, you need to call:
IvParameterSpec iv = new IvParameterSpec(bytIV);
This is an AlgorithmParameterSpec, and can be used as the third argument to the init() function for Cipher to set up decryption, e.g.
Cipher cd = Cipher.getInstance("DES/ECB/PKCS5Padding");
cd.init(Cipher.DECRYPT_MODE, sk, iv);
I believe that CBC mode is more secure than ECB mode when you have more than 8 bytes of material to encode (e.g. use "DES/CBC/PKCS5Padding"
when you create the Cipher objects).
To simplify things a bit, you might just want to use a fixed 8-byte Initialization Vector by constructing a IvParameterSpec and using it for all DES encryption and decryption.
The documentation on all of this is extraodinarily obscure.

Keeping Power Spectrum Peaks on a Graph

Hello,
I am trying to read in a signal which varies in frequency as time progresses. I am taking this function and running a real time power spectrum (FFT Power Spectrum.vi) on it. As time goes the peaks move around according to teh frequency which is coming in. What I want to do is to keep the old peaks on the graph as the new peaks come in. So for example if I had a signal which was at 50 htz then 75 htz, at the end of the run I want to see both peaks on my grpah. Is this possible? Thanks.
Intern NSWCCD Carderock.

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- tbob
Inventor of the WORM Global
Attachments:
SpectralMeasure.vi ‏98 KB

Convert power spectrum back to original waveform

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