Expert: Cezar L. Palconet Date: 10/30/2007 Subject: Is low-bandwidth FM video possible?
Question Hi:
What is the lowest frequency an FM carrier signal must be in order to transmit uncompressed luminance [Y] video signals with the least degradation in video quality?
My guess is its around 50 MHz. Am I right?
Is there any way to lower the minimum-required frequency down to 300 Hz -- lowest ULF signal? [yeah, I know that's a HUGE decrease in frequency]
Would converting the Y-signal to QAM [a technique used by dial-up modems to pack many bits into a signal without using much bandwidth] with 1 baud but 1-billion-bits-per-baud help? Would this cause the resulting FM signal to take up less bandwith and decrease the distance of the sidebands from the carrier frequency?
Using many bits-per-baud with a low baud rate seems to be effective in conserving bandwidth while still getting the signal across with the least distortion.
Is it possible to do this?
Thanks,
Green
Answer 50 Mhz. would be about the lowest frequency that you could use to carry a TV signal with a bandwidth of 6 Mhz. with a commercial quality, otherwise it would be like Slow scan TV used in HF, this is not commercial quality, just great for amateur work. Check out ARRL for slow scan TV.
It is not possible for a bandwidth to be equal or greater than the carrier frequency, 300 Hz. As carrier, Is just like shooting the stars with a sling shot, and expect to hit it.
QAM is a final stage modulation, thus cannot be selective on what it would modulate in a composite carrier, the best you can do is digitize the signal, then modulate using QAM, but then that would sound like a digital receiver is needed to demodulate the carrier, then you are trying to re-invent Digital TV broadcast, which has been in place for quite sometime.
