Re: Anyone have access to a VHF spectrum analyzer?

Grant wrote:
What I'd ACTUALLY like to know, is approximately how constant in amplitude the 19 kHz stereo pilot sidebands are when program audio is present. This would mean looking at +/- 19 kHz away from the RF carrier center frequency with a fairly narrow spec an bandwidth to avoid sidebands due to program audio.



"Phil Allison" <philallison@xxxxxxxxxx> wrote in message news:6rakfsFbeenU1@xxxxxxxxxxxxxxxxxxxxx
"Grant"
I'd appreciate if someone could do me the favor of making a measurement off
the air of any stereo FM broadcast station. I'm interested in the approx
sideband levels. Nothing fancy, maybe 5-10 minutes to do.

** As already pointed out - sideband levels depend on the instantaneous program levels and frequency content.

The largest deviation from centre frequency allowed for commercial FM radio is +/- 75 kHz, while the highest modulating frequency is about 53kHz for stereo FM.

Generally, the whole signal spectrum will be included within +/- 100 kHz of the carrier frequency, with only very small residual levels outside that range.

Frequency dependant program limiting is included in the audio processing chain to make sure this remains the case.

Now, how about you tell us what you ACTUALLY wanted to know ???



..... Phil


Frequency and phase modulations do not belong to what are called "linear modulations". In few words this means that the modulated signal obtained in response to a pilot tone alone and the modulated signal corresponding to a pilot tone plus something else have nothing in common.

Even the case of a carrier being frequency-modulated by _one_ sinusoidal signal is rather complex: you end up with an (theoretically) infinite number of lines computed from bessel functions. The response to _two_ sinusoidal signals is _not_ related to the prior response.

In view of this, perhaps you may reconsider what you are looking for.

Pere
.

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