MC1374 TV modulator

[deepakrajchris]

I need information about this IC . . . . I read the data-sheet,which says it performs AM & FM and its freq. is 105Mhz. . .I need to know how the freq. 105MHz is generated. . .i need that formula. . .the circuit is given in the data-sheet itself. . . .Since it performs AM & FM the input must be analog ,am i right??? mainly i need the formula for the output frequency????

 

[JimB]

Looking at the datasheet the frequency is determined by the coil and capacitor connected between pins 6 and 7.

In figure 4 of the datasheet, C=56pF and L=0.1μH, this gives about 67Mhz.

If you want a formula for calculating the frequency, try ths:

F= 160/(√LC)
Where
F is the frequency in Mhz
L is the inductance in μH
C is the capacitance in pF

JimB

 

[deepakrajchris]

But have a look at the general information,it says MC1374 operates in frequency of 105MHz. . . . . . . If so i need calculations for 105 MHz as you have given above my friend...............

 

[RCinFLA]

The IC is intended for TV video with FM audio carrier as a sideband modulation on the AM RF. The FM oscillator runs from 1.4 MHz to maximum of 14 MHz. It is the reverse of the intercarrier FM I.F./demodulation system used in TV receivers.

If you are looking for an FM modulator for commerical FM band you could generator an AM RF carrier (with no video AM modulation applied) at, say 110 MHz with FM subcarrier set at 5 MHz to get a 105 MHz FM carrier.

Realize this FM carrier is just an AM sideband that will exist 5 MHz below and above the 110 MHz main RF carrier and its amplitude relative to the RF main carrier is about 20 db or less below the main RF carrier level. This low level is done to keep most of the AM modulation range for the video modulation. Too much FM subcarrier or too much video will exceed 100% modulation on the AM modulator.