Modulation depth

[MVK]

Hello andy,

still i have confusion of finding modulation depth positive and negative for AM as well as FM signal.

In general modulation depth will find over in the carrier signal am i correct? if it so, in the NI RFSA example vi's modulation depth found out after demodulation. i mean after demodulation we will get message signal using this signal only modulation depth calculation done in LabVIEW example vi's.

please make me clear on this. i am under confusion. i dont know how to find out positive and negative depth. and one more thing , i was trying to go thru' modulation depth example. in that example single to freq & amplitude measurement.vi could be used. in that two vi used i dont remember that vi's names it is some thing FFT measurement and time signal measurement vi like that. i was trying to look in to code but i unable to go in side . LabVIEW asking password for that case. actually i want to know how the amplitude can be calculate. in that vi is used for calculate "detected amplitude, detected frequency & phase".

other wise tell me how to find out modulated signal High amplitude value and low amplitude value. becaz this is only positive and negative modulation depth for AM signal right.

i have done small modification example vi to find out +ve & -ve modulation depth. i think i am wrong in that. please make me correct.please find the attachment for both AM & FM 

[Andy_Hinde]

Hello MVK,
My understanding of AM Modulation Depth is that it cannot be negative, so I am confused by your question. Here is the formula for Modulation Depth:

modulation depth = (a–b)/(a+b)
where

a is the unmodulated carrier amplitude, and
b is the minimum amplitude deviation.

Link to NI Developer Zone where this is defined:
http://zone.ni.com/devzone/nidzgloss.nsf/webmain/15E49C69DE87743F86256F8E007DD7E1

So, in order for this to be negative, the minimum amplitude deviation must be greater than the carrier amplitude, which would cause overmodulation and disrupt the signal. Am I misunderstanding your question?

Thanks,
Andy

[profesional]

hello pls help me with this.

1. what is the formula for depth of modulation

2. modulation index

[profesional]

pls help me to solve this question.

A 100v,100khz carrier is modulated by the help of a 1khz signal to the extend of 50%

(a) find the necessary parameters of the AM wave and write down it equation

(b) determine the amplitude of the modulating signal

[rooter]

please kindly forword the above zip file to me please .its very urgent

[altenbach]

---

@rooter wrote:

please kindly forword the above zip file to me please .its very urgent

---

That zip file was posted 9 years ago and can be downloaded by simply clicking on it. There is nothing to "forword", whatever that means.

(... and if you mean "forward",  you don't even provide any forwarding information!)

[rooter]

am finding it difficult to open it.please help me out. this is my mail

ernestdei2007@yahoo.com

thanks

[Andy_Hinde]

Hi Rooter,

I uploaded the ZIP file to the following FTP site:

ftp://ftp.ni.com/support/rf/Rooter/

I also opened the ZIP file and the two LabVIEW VIs that are contained in the ZIP file are also posted for individual download. You can download those instead if you are still having trouble opening the ZIP file.

Thanks,

Andy Hinde, MBA

Senior Systems Engineer

RF and Communications

National Instruments