Task about FM system modulation

[TRIDIP]

In an FM system freq deviation is 4 khz when the modulating voltage is 3V & modulating freq is 400hz.If the mod freq increases to 1000hz & its amp to 5 V,then mod index will 1.remain same 2.increase3.decrease????

An FM wave is 100% modulated by 10 khz signal,Hw much BW require???

anybody knw answer plz reply

 

[claudiocamera]

Re: FM

In an FM system freq deviation is 4 khz when the modulating voltage is 3V & modulating freq is 400hz.If the mod freq increases to 1000hz & its amp to 5 V,then mod index will 1.remain same 2.increase3.decrease????

An FM wave is 100% modulated by 10 khz signal,Hw much BW require???

anybody knw answer plz reply

Modulation idex is defined as β = Δf/fm

Where Δf is frequency desviation which depends on the modulation signal amplitude (voltage) ( two values in the question).
fm is the instantaneous frequence of modulation signal ( two values in the question)

If you consider theoretical formula given above you should compare the ratios 5/3 to 1000/400 where the first is lower, so modulation index will decrease.

In the second question the answer for BW cannot be given precisely since you can consider Carlson's Rule or Universal curves these methots give diferent answers.
If you take Carlson's Rule you just use its formula BW =2Δf(1+1/β)

β=1 => Δf=10khz the answer probably is 40Khz

Regards

 

[TRIDIP]

Re: FM

thanks for your reply,in 2nd question 100% modulation means is β=1??