From Newsgroup: uk.telecom

Op 2-2-2026 om 18:56 schreef David Woolley:

On 02/02/2026 15:14, The Natural Philosopher wrote:

Take analogue TV, the audio may be considered to be on a separate
transmitted frequency, but the chroma is-a multiplexed onto the same
'channel' as the video.

The way it is specified, and the way that analogue TVs recovered the
audio, is that both audio and chroma are on sub-carriers, not one on a sub-carrier, and one as an adjacent carrier.

An analogue tv signal was transmitted via two transmitters:
One for video (vestigal sideband modulation) on the channel frequency,
One for audio on a frequency 5,5 or 6 MHz higher than video frequency.
Some TV systems used FM for audio, some used AM.
Later the BBC used NICAM for audio. (was NICAM on another frequency?)
Tugether they form the "TV-channel", with a bandwidth of about 7 MHz.
In VHF the channel width was 7 MHz (for B & G),
in UHF 8 MHz.

Chroma was modulated on a subcarrier with an exact frequency of +
4.43361875 MHz for PAL.

More info here:
<https://en.wikipedia.org/wiki/Analogue_TV>

Analogue TVs recover the
audio as a 6MHz signal, embedded within the demodulated vidwo, and feed
it into a 6MHz IF amplifier; they don't down convert to, say, the
10.7MHz IF typically used for FM broadcast sound.

Analogue TV receivers use an Intermediate Frequency.
For B and G-system, as used in The Netherlands and Germany
this IF filter was from about 33 to 40,5 MHz.
You were tuned correct if the video carrier was on 38,9 MHz
and the audio carrier on 33,4 MHz (B & G audio was on +5,5 MHz).
There was no 6 (or 5,5) MHz IF amplifier,
the audio was demodulated from 33,4 MHz in case of B/G.

(Note that 6Mhz is for the UK.-a Other sub-carrier frequencies were used
in other countries.)

Chroma is interesting, because, if you treat it as a single sub-carrier,
you have to treat the modulating signal as being a complex number.

I'm not sure what you mean with this.

Rink
--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: uk.telecom

On 23/03/2026 19:20, Rink wrote:

An analogue tv signal was transmitted via two transmitters:
One for video (vestigal sideband modulation) on the channel frequency,
One for audio on a frequency 5,5 or 6 MHz higher than video frequency.
Some TV systems used FM for audio, some used AM.
Later the BBC used NICAM for audio. (was NICAM on another frequency?) Tugether they form the "TV-channel", with a bandwidth of about 7 MHz.
In VHF the channel width was 7 MHz (for B & G),
in UHF 8 MHz.

NICAM was on a subcarrier.

Lower power sites transposed the whole signal as video + sound + chroma
+ NICAM etc.



--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: uk.telecom

On 23/03/2026 19:20, Rink wrote:

There was no 6 (or 5,5) MHz IF amplifier,
the audio was demodulated from 33,4 MHz in case of B/G.

See the module at that top centre of the circuit diagram at <https://www.reddit.com/r/electronics/comments/l87rri/blackwhite_crt_tv_circuit/>;
that's the sound IF amplifier!

Also see <https://en.wikipedia.org/wiki/Intercarrier_method> and figure
3 in <https://www.worldradiohistory.com/Archive-Company-Publications/Aerovox/40s/Aerovox-1949-06.pdf>.

Chroma is interesting, because, if you treat it as a single sub-
carrier, you have to treat the modulating signal as being a complex
number.

I'm not sure what you mean with this.

Chroma is transmitted as a quadrature signal. There are effectively two carriers on carriers at the same frequency, but at 90 degrees apart in
phase. Describing such a system digitally, you would treat the I
component as real, and the Q component as imaginary.
--- Synchronet 3.21f-Linux NewsLink 1.2