How to find out +ve & -ve modulating depth?

[MVK]

Hi,

I had a small doubt in the RFSA. If you look in to any RFSA standalone instrument there is a option provided to find out modulation depth in positive and negative for AM as well as FM (frequency deviation). But as such in the NI RFSA nowhere I can see to find out modulation depth in positive and negative for AM as well as FM (frequency deviation). Only I can able to see general Modulation depth or Frequency deviation. But I want to know how to find out positive and negative modulation depth and also positive and negative frequency deviation. If anybody knows please let me know more about it.

Note: To find out modulation depth I am using NI RFSA 5660 module.

[Andy_Hinde]

Hello,
The MT RFSA Demodulate FM.VI example for FM demodulation with the PXI-5660 calculates peak FM deviation. Also, the example provides the demodulated message signal which will allow you to calculate the FM deviation in any manner you wish using the power of LabVIEW's analysis tools. The same situation applies for the AM example, which provides the carrier amplitude and the demodulated AM waveform. You can also calculate any type of modulation depth from these parameters using LabVIEW as well.

Regards,
Andy Hinde
National Instruments

[rajeshj]

Hi,

Following are the formulas for finding AM Modulation depth:

PEAK + mehtod: m = 100 * ((Emax - Eavg) / Eavg )

PEAK - method: m = 100 *((Eavg-Emin)/Eavg)

AVG method: m= 100 * (Vrms/Eavg)

Acquire the signal, demodulate it, use the formulas for finding the modulation depth.

Hope I have answered your question.

Regards,

Rajesh.

[MVK]

Thank you so much Mr.Rajesh.

I have seen your reply very late. as of now i dont have any hardware with me to cross check ur formula. I can check after a week only. so propably i can reply to you by this month end. I will try to do the same. I will get back as soon as possible.

I am having a doubt in ur formula.After demodulation i will get the message signal. In that signal i can find out Vrms(RMS voltage), But remaining Emin, Emax and Eavg how can i findout? and what it is exactly. can u pls explain....!

Message Edited by MVK on 10-18-2005 03:50 AM