ask modulation and demodulation

[supersky]

i am new to labview
pls help me to build ask modulation and demodulation without modulation toolkit

[tbob]

First of all, learn Labview basics.  Go to a class, buy a book, look at online tutorials.

I am assuming you know what ASK is (Amplitude Shift Keying).  You would have to sample the modulating signal to see when it is high and low.  You could use one of Labviews Function Generators to generate the carrier wave.  The amplitude would be set according to the modulating signal.  You need to do this inside a loop.  This is all very complex for a Labview newbee.  You need to learn about loops and event structures, also producer-consumer architecture.  I am thinking that the producer loop would constantly sample the modulating signal.  When it switches, you send a signal to trigger an event in the consumer loop.  The event case would change the amplitude of the carrier.  This is far above newbee level, but take a stab at learning Labview, then try to build your own vi.  We can then help you with any troubles.

For demodulation, the producer loop would sample the incoming modulated signal.  It would then trigger an event in the consumer loop when the incoming amplitude changes.  The event case would change the output level of the demod output.

[C-gis]

Hello:

Well i'm kind-off new to LabView and at the same time trying to develop an interface for ASK-Amplitude Shift Keying. However, can someone help me with both  front-panel and block diagram of an ASK VI, as i need it A.S.A.P.

Any help at this time will be highly appreciated.

[tbob]

What have you done so far?  You need to start off by writing some code, then asking for help when you get stuck.  Too many people want us to write their code for them.  Look for examples (Help - Find Examples) on modulation or amplitude modulation.  This will give you something to start with.

[C-gis]

Sure i have been working on the ASK. I did created VI interface that has the message signal and that of the carrier signal. However, i need directions regarding the block diagram -meaning, how to wire the block diagram that will output an ASK modulated signal.

[tbob]

Without the modulation toolkit, it will be very difficult to create ASK.  You can start by looking up Amplitude Shift Keying in Wikipedia.  They give formulas for creating the modulated carrier.  You will have to use Labview math functions to duplicate the formula.  Not an easy task.

This will be very time consuming.  I'll be happy to answer any questions you have.  But you will have to begin by writing some code and then posting it here when you run into problems.

[johnsold]

Actually, amplitude shift keying is trivially simple at the transmitter.  Select amplitude values to represent the two boolean states of a data bit.  Multiply the carrier by the selected value.  If the values are 1 and 0 then you have on/off keying as is often used with Morse code.  If the values are 0.99 and 1.01, it will be almost impossible to demodulate successfully if any noise is present.

If your channel has relatively little noise, demodulation can be as simple as finding the maximum value in each bit time and comparing that the the values selected for the two states.

Lynn

[tbob]

Lynn, you make it sound easy.  And now that I remember what it is (on-off keying), it is pretty trivial.

Wikipedia makes it look like rocket science:

Out of the transmitter, the signal s(t) can be expressed in the form:

In the receiver, after the filtering through h_r (t) the signal is:

where we use the notation:

n_r(t) = n(t) * h_r(f)

g(t) = h_t(t) * h_c(f) * h_r(t)

where * indicates the convolution between two signals. After the A/D conversion the signal z[k] can be expressed in the form:

Convolution???  On simple on-off keying, or simple amplitude shifting?  Wikipedia's explanation is convoluted.

[johnsold]

tbob,

I saw that too.  That approach may make sense for mathematical analysis of the behavior, especially for the case where neither amplitude is zero or for cases where more than two levels are used.

Lynn

[C-gis]

Thanks a million, as i'm on it rite now