More reading is required before I start to understand some of these posts. VLF filter doesn't stand for very low frequency? Strange tothink the "superior TV" signal is actually just AM.
Yes, VLF is very low frequency. If you think about an FM radio signal, the broadcast modulates slower for a low voltage, higher for a higher voltage coming out of the FM IF section/demodulator. This signal is also known as the Base-band signal. If your tuning is off one way, the output of the IF demodulator voltage goes higher. It goes lower as your tuning on the station is too low. Actually, the same would happen if your tuning is centered, but, the FM broadcast happen to be sending say something like a 1 Hz tone as the output would swing up and down in voltage very slowly. The output of the FM demodulator is usually put through a cap in series to remove this DC low frequency offset in case your tuning isn't dead center. However, if you filter out all the high frequencies (ie the audio in the broadcast) on this output, and only keep the DC, you now have a DC voltage offset based on your tuning position offset (Note: if the FM broadcast has a 0.1hz tone in it, this cap would also probably go up and down in voltage once every ten seconds). This DC is all too easy to extract, just take the output of the IF demodulator, place it through a 100K resistor and then a 10uf cap to GND. The voltage on that cap will have a DC voltage position based on your tuning position. To remove the DC and get just the sound, place 1 uf cap in series at the output of the demodulator and tie a 100k resistor to GND on the other side. At the output of that cap, there is no DC, just the higher frequency, or the audio.
As for TV, yes, it's a 6MHz bandwidth AM broadcast as for when you have reflections in you receiver antenna, since video is so much faster than audio, down to 70ns, since the reflections have traveled a different distance from the broadcast tower to your TV antenna, ghosts will appear, but, the picture is still visible. If it were an FM broadcast, not only will there need to be more parts since TV started in the vacuum tube era, but you will get speckles all over your image instead of a ghost transmition as the FM receiver tries to discriminate between what to show in the mix of 2 or more signals of the same image coming in at different times. Things get worse if you have 2 overlaying broadcasts mixed together. For TV and over the air, AM is a only viable solution. The embedded 4.5Mhz audio needs to be narrow and low quality since it is so close to that color chroma at 3.57Mhz. It is also easier in AM transmitter and receiver to get the close to the full broadcast bandwidth of each channel.
As for analog satellite TV, since the broadcast was line of sight with no reflections, so they could broadcast in FM. This is why, with a C/KU band analog dish with a cheap proper analog receiver, the broadcast was near lossless, as if you had a wired connection to the source. The audio also was now moved to 6.2 Mhz and 6.8 Mhz, independent stereo with full 200Khz FM bandwidth on each channel making for near CD quality audio if your receiver's 2 audio FM tuners were good enough. Sometime there would be 4 channel audio with additional sound channels at 5.2Mhz, 5.8 Mhz, and even more in the 7 and 8 Mhz as the bandwidth for analog satellite TV was usually up to 25Mhz per channel, though, usually the first 5 to 6 Mhz was reserved for the picture allowing close to 600 lines of resolution with good equipment. The scrambled channels on analog satellite TV f--ked everything up as they messed with the black levels and color burst level. Those idiots at General Instruments who made the VCRS scrambling system developed the video level system for some weird Japanese non-standard Betamax video output levels and messed with the colors since they regenerated the color reference color burst signal at broadcast which was needed to be used as a clock to sync for their encrypted digital audio and the video output had the video sync and color burst regenerated on the decoder card in your receiver which never matched the original broadcast source levels messing up the tint and saturation and with the regenerated sync amplitudes, they messed up the black level.