ABM (Terrestrial): Frequency Finder. Birdman's thread

[Huevos]

I was wondering if being able to save the list of currently-used channels and just use those for a quick-scan we could do away with maintaining the transmitter data completely.

1) If you do away with transponder data you can only do a slow scan based on the bandplan.

2) If you have your channels in a bouquet and the mux moves to a different frequency a "system scan" will make the channels in the bouquet work again without changing anything in the bouquet.

[birdman]

1) If you do away with transponder data you can only do a slow scan based on the bandplan.

Not if you save the resulting found muxes. For any future scan for service-channel changes between muxes/additions/deletions) you can just scan those.

[Huevos]

Not if you save the resulting found muxes. For any future scan for service-channel changes between muxes/additions/deletions) you can just scan those.

That is exactly what the "DVB-T frequency finder" does. It saves the current active muxes. Then on each subsequent scan we just read the service data from "SDT actual" and "SDT other". We read all that data from one single transponder and the scan is completed in a few seconds. But this only works for providers that store all data on a home transponder.

[EMJB]

The Topfield community have bypassed many of the problems of frequency changes by defining both the pre- and post- change frequencies as if they were separate transmitters - e.g.:

Sudbury Pre 1/8/2018 ............

and

Sudbury Post 1/8/2018 ......

Most importantly with this approach, no-one should be left unable to use the recorder for Freeeview while files are updated. The number of updates to the files is much reduced, even though the number of changes each time will be greater, so updates can be done at the author's convenience which seems far more sensible to me. All the necessary information is available months ahead, but unfortunately that already collected for the Topfield PVRs is SD only (though if I understand ABM correctly, or when using a network scan, it only requires the BBC1 SD frequency in the file) .

EMJB

[Huevos]

The Topfield community have bypassed many of the problems of frequency changes by defining both the pre- and post- change frequencies as if they were separate transmitters - e.g.:


and


Most importantly with this approach, no-one should be left unable to use the recorder for Freeeview while files are updated. The number of updates to the files is much reduced, even though the number of changes each time will be greater, so updates can be done at the author's convenience which seems far more sensible to me. All the necessary information is available months ahead, but unfortunately that already collected for the Topfield PVRs is SD only (though if I understand ABM correctly, or when using a network scan, it only requires the BBC1 SD frequency in the file) .

EMJB

First that means scanning muxes that are not active.

if I understand ABM correctly, or when using a network scan, it only requires the BBC1 SD frequency in the file

Don't confuse ABM with a network scan.

Network scan will not work for uk tv because there is no frequency data in the SI tables for any of the T2 muxes.

ABM scan, the frequencies of T2 muxes for each area are listed in the providers file.

[ccs]

Am I the only one who is now totally confused, and haven't a clue what is/isn't going on???

[abu baniaz]

You need to tune in to the right frequency to understand what is going on.

[EMJB]

First that means scanning muxes that are not active.

Why? You simply select the version that is relevant to the current date, i.e. with the example I used one week ago you would have selected the "Sudbury Pre 1/8/2018" entry, and today the "Sudbury Post 1/8/2018" entry. This seems to have worked well for Topfield users through the digital changeover shuffles and the beginning of the 700 MHz clearance.

Don't confuse ABM with a network scan.

I appreciate that they are totally different, but they share a common problem, i.e. the need for data tables that are a pain to keep up to date (and cater for the 1000+ transmitters!).

Network scan will not work for uk tv because there is no frequency data in the SI tables for any of the T2 muxes.

I had not appreciated that. As I believe it can cause problems with picking up the lower power version of a mux in the overlap regions of main and fill-in stations*, could it please be automatically disabled in some way for the UK?

EMJB

* I did some experiments with the network scan 18 months or so ago. The SI tables for the main stations seemed to include the frequencies of all the associated fill-in stations, and those of our local fill-in station seemed to include the frequencies of the main station and of the other fill in stations (logical from the broadcasters viewpoint as then the fill-in station simply retransmits the main station signal without the complex logic needed to change SI tables). Thus a network scan for a fill in station will include the main station frequencies, which may be detectable but weaker than those from the fill-in station. There did not seem to any logic to use the stronger signal, but IIRC the first to be found was used - i.e. only 50% chance of using the right one. Incidentally, for the same reason the fill-in stations transmissions include the EPG data for all the muxes even though only 3 are transmitted - something that ABM failed to deal with at that time so that the bouquets included a large number of programme channels that had EPG data but could not be watched.

[abu baniaz]

Please submit pull requests for the required changes to Enigma2 scanning.

[Huevos]

The SI tables for the main stations seemed to include the frequencies of all the associated fill-in stations, and those of our local fill-in station seemed to include the frequencies of the main station and of the other fill in stations

This is not correct. The main mast only contains data related to the main mast. Repeaters only contain data about the main mast. For this reason trying to do a network search of a repeater is pointless. And any network scan done in the UK of the main mast will not return unknown T2 muxes.

I believe it can cause problems with picking up the lower power version of a mux in the overlap regions

The only time that would happen is if you were scanning a repeater.

There did not seem to any logic to use the stronger signal, but IIRC the first to be found was used - i.e. only 50% chance of using the right one.

Use the correct region in your tuner config so only the correct muxes area scanned. If you want to scan in 2 identical muxes turn on namespace subnet for DVB-T. If you only want to scan the strong version of any particular mux use the TerrestrialScan plugin.

[bbbuk]

In my previous post, I have identified the new frequencies for Winter Hill but these are happening in stages between now and middle of 2020.

Would it be easier if ABM was extended to include retrieving latest terrestrial.xml, satellites.xml, etc directly from source (ie github) similar to provider files. These can be stored in /etc/enigma2. This option would allow more quicker/robust updates for users by simply doing a "provider" update without need of Vix to rebuild images with that have these changes.

[abu baniaz]

ABM does not use the files used for Enigma2 scanning. In any case, somebody would have to update them anyway.

In any case, we only included the "clash regions" and a few others for terrestrial. Terrestrial frequencies do not change that often.

We have provided the tools to make it easier for people to submit updates to XML files.

[abu baniaz]

There is the XML update plugin to fetch updated enigma 2 scanning files.

[Huevos]

In my previous post, I have identified the new frequencies for Winter Hill but these are happening in stages between now and middle of 2020.

Would it be easier if ABM was extended to include retrieving latest terrestrial.xml, satellites.xml, etc directly from source (ie github) similar to provider files. These can be stored in /etc/enigma2. This option would allow more quicker/robust updates for users by simply doing a "provider" update without need of Vix to rebuild images with that have these changes.

As mentioned above "xmlUpdate" already does that.

grab10.jpg

grab11.jpg

grab12.jpg

[birdman]

That is exactly what the "DVB-T frequency finder" does. It saves the current active muxes. Then on each subsequent scan we just read the service data from "SDT actual" and "SDT other". We read all that data from one single transponder and the scan is completed in a few seconds. But this only works for providers that store all data on a home transponder.

So it isn't actually what I suggested, as I suggest remembering all available muxes and scanning just those. As had been noted (in this thread?) the main DVB-T muxes don't refer to any DVB-T2 ones.