You guys are testing my gray matter today...
The question: Is it possible to detect an FM subcarrier without
receiving the base carrier?

Perhaps another cup of coffee will help...


On Mon, 26 Dec 2005 18:05:38 -0500, "Fred W4JLE"
wrote:

65.75 is the magic frequency. It does appear the WFM mode can not be used on
this frequency on the 706 MKIIG I have. In the FM position, while distorted
it is copyable. The radio shows WFM mode, but it certainly isn't in the wide
mode.

Now I have to get in the circuitry and see why the WFM is not operable on
this band.

"Cecil Moore" wrote in message
. net...
Fred W4JLE wrote:
You can if you tune to the audio offset.

I have run the IC-706 all up and down the channel 3
60-66 MHz frequencies while in College Station, TX
and cannot hear the audio anywhere.
--
73, Cecil http://www.qsl.net/w5dxp

John Ferrell W8CCW

"John Ferrell" wrote
The question: Is it possible to detect an FM subcarrier without
receiving the base carrier?
______________

If you are still thinking of the broadcast television signal, the audio
portion is not a subcarrier -- it is a discrete carrier whose modulation can
be detected by any receiver capable of FM demodulation, and able to tune to
its r-f center frequency.

RF

Richard Fry wrote:
If you are still thinking of the broadcast television signal, the audio
portion is not a subcarrier -- it is a discrete carrier whose modulation
can be detected by any receiver capable of FM demodulation, and able to
tune to its r-f center frequency.

The confusing part, at least for me, was that the entire passband *can
be* downconverted and then demodulated assuming 4.5 MHz separation. That
doesn't imply a *necessary* condition for demodulation.
--
73, Cecil http://www.qsl.net/w5dxp

Richard Fry wrote:

If you are still thinking of the broadcast television signal, the audio
portion is not a subcarrier -- it is a discrete carrier whose modulation
can be detected by any receiver capable of FM demodulation, and able to
tune to its r-f center frequency.


You've described how it's commonly generated. But is the end result any
different than if it were generated instead by modulation of the main
carrier by an ideal modulation system not having the practical problem
of intermodulation distortion? That is, isn't the end result identical
to a subcarrier?

When I worked in radio broadcasting in the '60s, we generated an FM
(SCA) subcarrier in addition to the stereo subcarrier by modulating the
transmitter. Some stations had multiple SCA subcarriers.

Roy Lewallen, W7EL

"Roy Lewallen" wrote
Richard Fry wrote:
You've described how it's commonly generated. But is the end result any
different than if it were generated instead by modulation of the main
carrier by an ideal modulation system not having the practical problem of
intermodulation distortion? That is, isn't the end result identical to a
subcarrier?
____________

No, in that an aural subcarrier would disappear without a visual carrier to
convey it. TV aural via a standalone r-f transmission system would not.

RF

Richard Fry wrote:
"Roy Lewallen" wrote

Richard Fry wrote:
You've described how it's commonly generated. But is the end result
any different than if it were generated instead by modulation of the
main carrier by an ideal modulation system not having the practical
problem of intermodulation distortion? That is, isn't the end result
identical to a subcarrier?

____________

No, in that an aural subcarrier would disappear without a visual carrier
to convey it. TV aural via a standalone r-f transmission system would not.

Sorry, I obviously failed to communicate my question. Let me try again.

With no information other than looking at the composite signal including
video and audio, would you be able to tell if it was generated by two
separate transmitters or by modulation of a single transmitter by the
video and an audio subcarrier? That is, if you could do the modulation
without generation of intermodulation products.

Roy Lewallen, W7EL

"Roy Lewallen" wrote:
With no information other than looking at the composite signal including
video and audio, would you be able to tell if it was generated by two
separate transmitters or by modulation of a single transmitter by the
video and an audio subcarrier? That is, if you could do the modulation
without generation of intermodulation products.
______________

Given all that, then no. But that isn't the reality.

RF

TV audio is not a sub-carrier. The audio is an independent transmitter from
the aural transmitter.

They may have come up with some other way since I worked at WXEL in the
fifties, but as a fifty's TV set still works today, I suspect the result is
the same.

"John Ferrell" wrote in message
...
You guys are testing my gray matter today...
The question: Is it possible to detect an FM subcarrier without
receiving the base carrier?

Perhaps another cup of coffee will help...

I like your answer best, probably because I understand how it works!

On Tue, 27 Dec 2005 13:46:45 -0500, "Fred W4JLE"
wrote:

TV audio is not a sub-carrier. The audio is an independent transmitter from
the aural transmitter.

They may have come up with some other way since I worked at WXEL in the
fifties, but as a fifty's TV set still works today, I suspect the result is
the same.

"John Ferrell" wrote in message
.. .
You guys are testing my gray matter today...
The question: Is it possible to detect an FM subcarrier without
receiving the base carrier?

Perhaps another cup of coffee will help...



John Ferrell W8CCW

It is not a sub carrier in the rf spectrum, meaning it can be fully
seen with or without any other carrier (video), but when detected in
the TV receiver it becomes a sub carrier of 4.5 mhz in the TV's IF.
The audio carrier is mixed with the video carrier to produce the 4.5
mhz.
Without the video carrier the TV receiver will not see the 4.5 mhz.

As others have said the sound carrier is usually generated by a
separate transmitter at the sound carrier frequency. But it could also
be generated as a sub carrier of the main video carrier with the same
results. It would still be visible in the RF spectrum just the same as
it is when generated by a separate transmitter. The main carrier would
also have to be present at the same time of course.

However if the TV video signal was an FM modulated signal rather than
AM then the sound sub carrier would not be visible without the main
video carrier if it was generated as a sub carrier.

The same happens with an FM broadcast SCA sub carrier or the stereo
sub carrier on the main signal. The main signal must first be
demodulated in order to demodulate any sub carrier.

73
Gary K4FMX


On Tue, 27 Dec 2005 23:28:16 GMT, John Ferrell
wrote:

I like your answer best, probably because I understand how it works!

On Tue, 27 Dec 2005 13:46:45 -0500, "Fred W4JLE"
wrote:

TV audio is not a sub-carrier. The audio is an independent transmitter from
the aural transmitter.

They may have come up with some other way since I worked at WXEL in the
fifties, but as a fifty's TV set still works today, I suspect the result is
the same.

"John Ferrell" wrote in message
. ..
You guys are testing my gray matter today...
The question: Is it possible to detect an FM subcarrier without
receiving the base carrier?

Perhaps another cup of coffee will help...



John Ferrell W8CCW