Another Kind of Signal History?
Posted: Sun Feb 04, 2024 7:49 pm
Looking for comments on an idea for a variant of @Simon’s excellent Signal History.
The context is Medium Wave AM BC DX – weak signals – when a carrier can be prominent, but ID relies on detecting the elusive audio.
24-hour Signal History graphs on a target channel have been very informative. However, “SNR” subtracting Noise from Level can read 25 dB or more (dominated by the carrier) without hearing anything at all. That is not a great audibility (let alone intelligibility) predictor, so what could work better for me?
I’m suggesting a narrow-band measure of sideband modulation (excluding carrier), relative to channel-local noise floor just beyond the modulation. That’s a crude analogy with measuring one person’s speech level in a room and comparing with the general hubbub.
For example, “modulation” could be measured from 100 Hz outwards to some chosen limit (e.g. 3 or 4 kHz), and “noise” across possibly 3 or 4 to 6 kHz beyond the centre frequency, depending on neighbouring channel activity. So, the two input parameters might be called (e.g.) “modulation limit” and “channel limit”.
Obviously, for best results, the limits need fine tuning on the day. It would ideal if the noise and modulation pair could be output for upper and lower sidebands separately. Including a value for the carrier would complete the picture.
Because the bandwidths are different, average spectral density per Hz would be a better metric than power.
The context is Medium Wave AM BC DX – weak signals – when a carrier can be prominent, but ID relies on detecting the elusive audio.
24-hour Signal History graphs on a target channel have been very informative. However, “SNR” subtracting Noise from Level can read 25 dB or more (dominated by the carrier) without hearing anything at all. That is not a great audibility (let alone intelligibility) predictor, so what could work better for me?
I’m suggesting a narrow-band measure of sideband modulation (excluding carrier), relative to channel-local noise floor just beyond the modulation. That’s a crude analogy with measuring one person’s speech level in a room and comparing with the general hubbub.
For example, “modulation” could be measured from 100 Hz outwards to some chosen limit (e.g. 3 or 4 kHz), and “noise” across possibly 3 or 4 to 6 kHz beyond the centre frequency, depending on neighbouring channel activity. So, the two input parameters might be called (e.g.) “modulation limit” and “channel limit”.
Obviously, for best results, the limits need fine tuning on the day. It would ideal if the noise and modulation pair could be output for upper and lower sidebands separately. Including a value for the carrier would complete the picture.
Because the bandwidths are different, average spectral density per Hz would be a better metric than power.
