How is Signal Quality calculated?

[pixelstuff]

In the HDHomeRun Config GUI, how is the Signal Quality meter calculated?

[Billi23]

SNQ Signal Quality is scaled for each modulation type such that 50% is the minimum signal-to-noise requirement.
For ATSC1, 100% SNQ is 30dB+ SNR, 50% is 16dB SNR.
For ATSC3, the HDHR scales the MER such that 50% is the near-minimum SNR required for the given modulation(s) used on the channel.

[pixelstuff]

How does it differentiate between the signal and the noise in order to get the signal to noise measurement?

I'm curious what is going on behind the scenes because I have some weak channels that can normally be watched but occasionally they completely drop out almost as if they don't even exist. The software shows some signal strength so it seems like they must be broadcasting, and my booster can bump that up into the 90% range easily, but the signal quality and symbol quality remain at 0% and nothing tunes in on that channel.

[kyl416]

The Signal Quality is how much of the actual signal could be decoded above the noise floor. The noise floor can be affected by anything from multipath interference by the signal bouncing off of any hills or buildings in your vicinity, another station on that RF number coming from another direction, or noise from things with motors or poorly shielded electronics like off-brand power supplies, cheap LED bulbs, neon business signs, etc.

Boosters in most cases only help with signal loss that occurs due to long cable runs and/or splitters, but they will also amplify any noise that is preventing you from decoding the signal. For longer runs it's best to use a preamp installed close to the antenna so the incoming signal is as clean as possible, and use a distribution amp or a powered zero loss splitter if you need to feed multiple TVs.

If you have a decent signal strength but low quality without the booster, it usually means there's noise interference you need to mitigate by either relocating your antenna, adjusting its aim, or replacing it with a more directional model with higher gain. Also, if the RF numbers giving you problems are in the 30s, it might be 5G interference from a nearby T-Mobile tower, so a 5G Filter might help. You can check this by tuning to RF 38 to see if you see a high signal strength.

[nickk]

How does it differentiate between the signal and the noise in order to get the signal to noise measurement?

Take something like QAM256 which is an 16x16 grid of boxes. With perfect signal each sample is exactly in the middle of the one box it was meant to be in. The MER measurement (basically SNR for digital) is a measurement of how far off each sample is vs the perfect middle of the box where it should be.

[pixelstuff]

How does it differentiate between the signal and the noise in order to get the signal to noise measurement?

Take something like QAM256 which is an 16x16 grid of boxes. With perfect signal each sample is exactly in the middle of the one box it was meant to be in. The MER measurement (basically SNR for digital) is a measurement of how far off each sample is vs the perfect middle of the box where it should be.

What is a sample in this case and how does the signal get mapped into a grid of boxes? Is each box a different frequency range? What does a shift up/down or left/right, in one or a few boxes, indicate is happening to the radio signal?