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Topic: Frequency response of FM Radio (Read 8371 times) previous topic - next topic
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Frequency response of FM Radio

Hi - Can someone pl tell me: What's the max frequency response and S/N ratio of standard FM radio broadcast? Rgds, Saugata

Frequency response of FM Radio

Reply #1 –
Quote
Hi - Can someone pl tell me: What's the max frequency response and S/N ratio of standard FM radio broadcast?

FM maxes out at 15khz. Signal to noise ration is pretty bad too, 50-60db is common depending on a variety of things - including mono vs stereo, received signal strength, etc.

But it's safe to assume 30hz-15khz, 56db sn.

Frequency response of FM Radio

Reply #2 –
IIRC, the lower limit is more like 50-55hz...
"You can fight without ever winning, but never win without a fight."  Neil Peart  'Resist'

Frequency response of FM Radio

Reply #3 –
This thread might be of interest...

http://www.hydrogenaudio.org/forums/index.php?showtopic=8109

The noise floor is frequency dependent (due to the pre-emphasis and the intrinsic rising noise-floor of FM).

It's not difficult to get a noise floor which reads -70dB relative to a full scale signal on a spectrum analyser. The nearest approximate digital equivalent to FM is a 14-bit 32kHz sampled signal.

In mono, the bandwidth of FM isn't strictly bounded, but stereo broadcasts are usually cut at 15kHz to protect the 19kHz pilot tone.

Cheers,
David.

Frequency response of FM Radio

Reply #4 –
Due to my analysis, the signal-to-noise ratio of my German cable FM radio is about 45dB FS. Measured with CEP, using a Sony MD recorder as AD-converter, highest peak to average RMS (of the noise), RMS window 50ms.
The frequency cutoff is at about 16 000 Hz.
More than 55dB STNR sounds almost impossible to me.
I know that I know nothing. But how can I then know that ?

Frequency response of FM Radio

Reply #5 –
Quote
Due to my analysis, the signal-to-noise ratio of my German cable FM radio is about 45dB FS. Measured with CEP, using a Sony MD recorder as AD-converter, highest peak to average RMS (of the noise), RMS window 50ms.
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That's true, but the "noise" you're measuring is a wide-band unweighted RMS value. 70dB from signal peak to noise floor on a spectrum analyser is still possible, because it's a completely different measurement. The spectrum level will (usually) be much much lower than the RMS.

An A-weighted RMS may be a fairer measurement, though it wouldn't make a huge difference. I'll see what I get via cable tonight if I get the chance.

Cheers,
David.