16-05-2024, 04:37 PM
Though the chips have two "carriers", one is created by modulating a subcarrier and then mixing it with a 2nd RF carrier same frequency as video carrier. So with the chip that has a direct aux in to by-pass the subcarrier AM or FM, you have to supply your own 6.5 MHZ digital subcarrier or 3.5 MHz AM. Presumably the block diagram doesn't show all the details of the RF end.
No doubt it's done this way so there is only one high frequency input divide by N. The UHF VCO seems to run at twice UHF carrier. The VHF being simply the UHF frequency divided by 2, 4, 8 or 16, hence squarewave out. I imagine close to a squarewave at UHF too, but there seems to be a UHF low pass filter.
The mixer for sound sub-carrier is likely a balanced kind, maybe even more complex to cancel the other side band.
No doubt it's done this way so there is only one high frequency input divide by N. The UHF VCO seems to run at twice UHF carrier. The VHF being simply the UHF frequency divided by 2, 4, 8 or 16, hence squarewave out. I imagine close to a squarewave at UHF too, but there seems to be a UHF low pass filter.
The mixer for sound sub-carrier is likely a balanced kind, maybe even more complex to cancel the other side band.
