Background channel scan: How to deal with tropo channels overwriting locals?

[Cabal]

I know the question of background scans, disabling them, scheduling them, etc, has come up many times. I already disable all distinct out-of-market channel numbers that come up with a background scan. This is not my issue.

It seems like once a week, I need to run a manual rescan because a background scan has pulled in an out-of-market channel (San Antonio digital 17.1) and overwriting my local Austin 17.1 (and 17.x) channels. What is the best way to fix this, besides constantly running manual scans?

The device in question is 1077341E.

It seems like background scans would be more productive in the 10 AM - 3 PM Local time frame.

Thanks.

[Señor Bob]

It seems like once a week, I need to run a manual rescan because a background scan has pulled in an out-of-market channel (San Antonio digital 17.1) and overwriting my local Austin 17.1 (and 17.x) channels. What is the best way to fix this, besides constantly running manual scans?

It looks like San Antonio channel 17 is RF 18 (494-500MHz) while Austin channel 17 is RF 35 (596-602MHz). If you could build a notch or band-stop filter[1] to knock down RF 18 that should stop it.

Another option might be to change the position of your antenna, so that RF 18 is too low in signal to be detected by the automatic channel scans.

[1]: https://en.wikipedia.org/wiki/Band-stop_filter

[Cabal]

All options no doubt, but I imagine there is improvement that can be made in the logic at the software level. This isn't the first time this problem has surfaced on these forums.

[gtb]

If you could build a notch or band-stop filter[1] to knock down RF 18 that should stop it.

A single channel notch filter tends to be rather expensive commercially (if you can filter a larger band, rather than just one channel, it can end up cheaper). Building it yourself is always a possibility, but unless you have the tooling to do so, it is probably still going to be cheaper to buy the filter commercially (if you need to filter a lot of channels, that gets to be a more interesting situation).

[gtb]

This isn't the first time this problem has surfaced on these forums.

Correct. And while various thoughts, ideas, and proposals, have been offered by the community over the years to provide owners of the tuners additional options, you are, for now, going to have to think outside the HDHR box for your solution.

[kyl416]

Not to mention notch filters aren't perfect, something blocking out San Antonio's KNIC-DT on RF 18 will likely affect Austin's KGBS-CD on RF 19.

A potential solution would be for them to start taking the TSID into account as that value is supposed to be unique. Like when the background scan gets a major-minor conflict, if the background scanned TSID doesn't match the TSID of the existing station, do not overwrite.

But ideally, it would be nice just to have a checkbox to disable the backgound scan in the System Configuration section where you have the send diagnostic information checkbox so those of us living in areas where even the slightest of boost conditions can cause conflicts can disable this function. Further east where the climate is more humid and the DMAs are more densely packed together, it is common to have atmospheric boost conditions on a nightly basis and extreme nights where you're pulling in stations from several DMAs away, so the last thing anyone should be doing is rescanning during those hours. Sometimes the boost conditions don't subside until the early afternoon, so if a channel you wanted to watch was overriden overnight, you can't even manually scan to fix it until later in the day.

It's not just a US thing either, over in Europe it's common for their DTT operators to put out alerts when a weather pattern favorable to boost conditions will affect reception. Even their cellular companies put out warnings since unintended international roaming in the 700 MHz and 800 MHz bands also happen during these conditions.

Some ATSC tuner boxes also do a background scan, although in their case they usually ignore the conflicts or assign them fake major numbers above 69.

[gtb]

Not to mention notch filters aren't perfect, something blocking out San Antonio's KNIC-DT on RF 18 will likely affect Austin's KGBS-CD on RF 19.

Extremely tight notch filters do exist (and have been used for commercial TV distribution systems). When I looked a decade or two ago they were in the many hundreds of dollars to start (and went up quickly depending on the requirements). Those solutions were targeted towards commercial (not residential) usage, so money was not really an object as long as it delivers on the requirements (which often included being rack mountable, so the form factor may not be your typical residential filter/pad cylinder, either).

[KeithAbbott]

Until now, I was not aware of any sort of background channel scan(s) occurring. Are these triggered internally within the HDHomeRun device, or does external software (e.g. HDHomeRun app for Windows/Mac/Linux etc.) trigger the background channel scans?

[Cabal]

Until now, I was not aware of any sort of background channel scan(s) occurring. Are these triggered internally within the HDHomeRun device, or does external software (e.g. HDHomeRun app for Windows/Mac/Linux etc.) trigger the background channel scans?

By the device. https://info.hdhomerun.com/info/webui#channel_lineup (under "Rescanning channel list").

Others:
Does the background scan timer get reset when a manual scan is run? I could fire off a daily lunchtime manual scan via script if that would block the background scans.

[pshanew]

Until now, I was not aware of any sort of background channel scan(s) occurring. Are these triggered internally within the HDHomeRun device, or does external software (e.g. HDHomeRun app for Windows/Mac/Linux etc.) trigger the background channel scans?

By the device. https://info.hdhomerun.com/info/webui#channel_lineup (under "Rescanning channel list").

Others:
Does the background scan timer get reset when a manual scan is run? I could fire of a daily lunchtime manual scan via script if that would block the background scans.

Try it and let us know?

[Cabal]

@nickk @NedS Does SD have a recommended approach for dealing with this challenge?