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  1. #1
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    EMJB's Terrestrial Channels brainstorm

    I am starting a new thread rather than continue the somewhat off topic discussions under the ABM heading.

    I suspect the vast majority of UK users have one or more TVs with the following features that seem to work without any problems:
    1. Finds all muxes giving a reasonable signal using only a country selection by the user, rather than having to select individual transmitter
    2. Where the same mux is available from 2 or more transmitters, chooses the optimum one (presumably based on signal strength/quality)
    3. Allocates a universally agreed numbering system
    4. Only displays channel and associated programme information for muxes that can actually be detected.

    with the only drawback I have noticed being the time taken (~ 5 minutes).

    When I first started to use Openvix (with UK terrestrial signals only), I found it very difficult to find what to do to replicate the television set's programme channel numbering etc - the published manual only contained satellite scanning info. Of the available options:

    • ABM required details of individual transmitters, which were incomplete and only updated days after frequencies were changed (e.g. as part of the 700 MHz clearance), and the channel lists and EPG data showed all channels in that region, even though only ~50% are available from fill-in transmitters - very disconcerting.
    • The automatic scan from the menu fails to cope with signals from multiple transmitters - I think the first found is used - and the programme channels are in what seems to the newbie to be a random order.
    • The manual scan from the menu depends on predefined transmitter details in a similar manner to ABM, and again does not order the programme channels.
    • The "Network scan" option in the menu for the automatic and manual scan defaults to "On", but this feature does not work correctly and can lead to problems when scanning for fill-in transmitters. The situation is further confused by the "terrestrial.xml" files apparently selecting a network scan, though I gather this part of the file is ignored.
    • The TerrestrialScan plug-in does not order or correctly number the programme channels, and in a quick look at the code I could not find any logic to deal with signals from 2 or more transmitters.


    The ABM and manual scan approaches do have the advantage of speed, but any solution that avoid needs to update files etc would be well worth the additiional scanning time in my view. It is perhaps worth pointing out that there are over 1000 UK Freeview transmitters, so any per-transmitter data files are likely to be incomplete.

    My apologies if changes in the last two years have invalidated some of the above - I have just found it all so frustrating that I have developed work rounds for my own use only.

    What I would dearly like to see is some instructions for the preferred way of duplicating the television set's programme channel layout etc, and some way found to discourage the alternatives (e.g. at a lower level in the menu system, or only visible when an expert mode is selected). It would be nice to follow the TV sets' example and completely avoid the individual transmitter selection, but if this is not practical it seems to me that giving a transmitter different entries for pre- and post- any change is the best solution.

    EMJB
    Last edited by Huevos; 12-08-18 at 16:42.
    Xtrend Xt10000 with 3 Freeview tuners

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  3. #2
    ViX Beta Tester birdman's Avatar

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    I'd add that scanning for muxes and sorting the resulting available service channels into an EPG order (bouquets) are two separate things. It should be possible to do one without the other.
    The bouquet creation will obviously require a lamedb file, but it should be able to use an existing one, so that you can re-order things if the options you tried first time didn't actually do what you really would like.
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    Moderator Huevos's Avatar

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    If you want to mimic what a Freeview compatible television set does use the TerrestrialScan plugin.

  5. #4
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    Reluctantly I have agreed to draft a guide to the "problem" of a "newbie" setting up a Freeview programme channel list to match that of all television sets, and thinking more about it the maintenance of that list needs to be addressed too. To produce the best possible guide, I believe 3 types of information are required:

    (1) A definition of the "problem" to be addressed - in this case pretty clear in the first sentence above.

    (2) A substantial understanding of the proposed solution to that problem, with particular attention to where user inputs or external data are required and under what circumstances the solution could fail.

    (3) An understanding of other facilities/settings that the user might be tempted to use which would have an adverse effect on the result.

    My attempts to get some of the information in (2) & (3) from other threads have largely failed, so below I have laid out a sort of "thought experiment" to elicit the information that would be needed to even provide a good framework for the sort of user guide referenced requested my first post. Wherever possible I have used situations that are, or at some time were, true, for me (or which I may be able to emulate with some indoor aerial juggling). I have also tried to pose questions that require as yes/no answer where possible.

    I must stress that the later scenario stages I have postulated are unlikely, and I would not consider it unreasonable if OpenVix did not always cope as one would wish. However I do believe the combination of user guide, error messages, and on-line help should not simply leave the user confused and lost, even if the answer is to post the contents of a particular file on this forum.

    The term "strongest signal" has been used elsewhere when probably the correct term would be "best" thus using signal to noise ratio rather than absolute signal level. I have retained the former term to be consistent with my sources of information.

    Scenario Stage 1:

    Fred is a newbie having just bought an E2 receiver with OpenVix installed, and only DVB-T/T2 tuner(s) fitted. He want to set up his receiver to receive all available programme channels numbered in the same way as his (or any other) Freeview television set.

    Q1.1 Is ABM the recommended method of achieving this?
    Q1.2 Is there any other method suitable for a newbie (i.e. does not involve fiddling with file contents or manually allocating channel numbers, and only takes a few minutes)?

    Clearly one of the early, if not first, actions Fred will need to do is set up the Tuners at Menu -> Setup -> Tuner Config -> Tuner Setup -> Tuner A/B/C etc. I understand Tuner Type, Config Mode, 5V .., and Force legacy stats, but:

    Q1.3 Am I right in thinking the country & region settings on each tuner page are for Enigma2 Scanning purposes only, and thus completely irrelevant while using ABM and when viewing/recording subsequently?


    Scenario Stage 2:

    Fred lives close to a fill-in transmitter (Burnham-On-Crouch, which transmits the PBS1/2/3 muxes only), which does not appear in the ABM "Provider" list.

    Q2.1 Is the use of SignalFinder the recommended action in this case?
    Q2.2 If not, what action is recommended?

    I understand that SignalFinder inserts an entry into the ABM "Provider" list, which the user then needs to select at Menu -> Setup -> Tuner Config -> ABM -> Providers.

    Q2.3 Is that correct?
    If so
    Q2.4 Does that information get lost if the ABM "Update config files" feature is used subsequently?
    and
    Q2.5 Does that information get lost when updating OpenVix subsequently?


    Scenario Stage 3:

    As well as picking up PSB1/2/3 signals from the Burnham-on-Crouch transmitter, Fred can also receive PSB1/2/3 & COM3/4/5 signals from the parent transmitter at Sudbury but these are weaker and unreliable in summer due to an intervening belt of trees. Thus he wants to receive PSB1/2/3 from Burnham. Receiving COM3/4/5 as well from Sudbury when they are strong enough would be a bonus. N.B. Moving the aerial is not an option as Fred lives in a block of flats with communal aerial.

    Q3.1 Am I right in thinking the two sets of PSB signals will be identical in all respects other than transmission frequency, notably having the same Transport Stream ID's (TsIds)?

    It has been stated that the SignalFinder identifies the "strongest" signals, which alone would be meaningless as the number of muxes is unknown (there may be 3-9 wanted muxes depending on transmitter, and 9 or more unwanted muxes would be possible). I have failed to find the SignalFinder code on Github to investigate. (Apologies for my statements elsewhere on this topic - I was confusing SignalFinder with TerrestrialScan). If the logic is the same as TerrestrialScan, my (very fallible) inspection of the code indicates that it identifies the "strong enough" signals and thus return all 9 frequency channels in the above scenario. SignalFinder "strongest signal" logic would only make sense to me if it was in fact something like "strongest signal for each detected TsId".

    Q3.2 Where is the SignalFinder code?

    Is the SignalFinder logic:

    Q3.3 "Strong enough", and if ABM cannot sort out the resulting duplicated programme channels, what error information is given to the user to help him sort out the mess? (And ignore scenario 4 below!)
    or
    Q3.4 "Strongest signal for each TsId"?
    or
    Q3.5 Something else?


    Scenario Stage 4:

    It just happens that the Crystal Palace transmitter is behind the Burnham transmitter when viewed from Fred's block of flats, so these can be detected (at least uder favourable atmospheric conditions) and SignalFinder may find these. Crystal Palace is in a different Freeview region from Sudbury/Burnham.

    Q4.1 Am I right in thinking that all the Crystal Palace signals will have different TsIds from the equivalent Sudbury & Burnham signals? (My argument being: PSB1&2 will carry different local programmes at times, and thus in general have different EPG data. As the EPG data for all Muxes is transmitted on each mux, PS3 & COM3/4/5 muxes will have different content, and thus different TsIds even though the video/sound is identical in the two sources).
    Q4.2 Will the SignalFinder logic recognise that the different TsIds from Crystal Palace and Sudbury/Burnham refer to the same muxes (which I suspect would involve tuning in to each frequency in turn and decoding the stream to obtain lists of programme channel names and compare them), and only report the stronger ones?
    Q4.3 If not, and if ABM cannot sort out the results, what error information is given to the user to help him sort out the mess?

    TerrestrialScan

    My next group of questions relate to TerrestrialScan, whose functionality superficially seems to be largely a superset of SignalFinder i.e. SignalFinder plus an "Enigma2 Scan" . I see it as being important that any users understand the limitations, so it is not used when it can do more harm than good. My questions is therefore which of the following are true in terms of selecting the frequency channels to be used for the final results of the scanning:

    Q5.1 All frequency channels with a detectable signal?
    Q5.2 The frequency channels with the strongest signal for each TsId found?
    Q5.3 The frequency channels with the strongest signal for each set of programme channels?

    My inspection of the code at https://github.com/OpenPLi/enigma2-p...estrialScan.py has failed to identify any code that might be implementing any "strongest signal" logic, so my assumption has been that 5.1 is true so it could report/search a total of 18 frequency channels (9 Crystal Place, 6 Sudbury, & 3 Burnham) in scenario stage 4.

    My understanding is that TerrestrialScan generates an entry in the transmitter list accessed at Menu -> Setup -> Tuner Config -> Tuner Setup -> Tuner A/B/C.

    Q5.4 Is this correct?
    and if so:
    Q5.5 Is this the same as the ABM "providers" list?
    or
    Q5.6 Are there separate lists for ABM and Enigma2 Scanning with overlapping information content?
    in which case:
    Q5.7 Are both updated by TerrestrialScan?
    and
    Q5.8 Are both updated by SignalFinder?

    Freeview Line-Up Changes

    The Freeview programme channel line-up is subject to quite frequent changes (which typically at ~2 month intervals), when existing channels may disappear/move position and new ones appear. Users may be tempted to use the TerrestrialScan or the Enigma Scan rather than re-run ABM. However at best it seems to me that these will have no beneficial effect on Fred as his bouquets to meet the original requirement will not be updated.

    Q6.1 Is that correct?

    and at worst he will lose (possibly all) programme channels due to the bouquets referring to lamedb entries that no longer exist if the new scan chooses different frequencies. If Fred selected a clear all bouquets option, he would simply be left with the psuedo-randomly ordered Last Scanned bouquet, so the original objective is most definitely no longer met.

    Q6.2 Is that correct?

    I think that there is another less frequent issue with changes to the Freeview line-up, and that is of changing programme channel names. I believe the normal practice is for television sets to automatically update the channel names at switch-on (or perhaps tune to that mux) without needing a channel scan, but a rescan with ABM, TerrestrialScan, or Enigma Scan is needed to do the necessary change to the lamedb files. Clearly only the ABM option can be recommended in view of the above.

    Q6.3 Is that correct?

    in which case I consider it desirable to warn Fred of this discrepancy between OpenVix and television set behaviour.

    ABM Bouquet Creation

    In order to produce the relevant bouquet to meet Fred's original requirement, the "LCN" values for each programme channel are needed. I am confused by some of the remarks elsewhere as to whether ABM gets this data from the transmitted stream or from a data file.

    Q7.1 Does the ABM rely on a data file for LCN values?
    Q7.2 ABM has a feature to remove certain categories of programme channels (e.g. porn) - am I right in assuming it depends on a data file?

    If ABM requires a data file for either or both purposes, there is likely to be a delay in that file being updated by the OpenVix team, during which time scanning with ABM and with a television set is likely to give different results for a few days (or weeks??) after any change.

    Q7.3 Does "Update config files" in the ABM menu update both this file and the provider file?
    Q7.4 What timescale can users expect a new file after a programme channel change (deletions, additions, or re-numbering)?
    Q7.5 How is the user to know when the new file is available as I don't think the dates of the current files are not readily available to the newbie user?
    Q7.6 There does not seem to be an equivalent to the "Update config files" for the Enigma2 Scan transmitter list offered at Menu -> Setup -> Tuner Config -> Tuner Setup -> Tuner A/B/C etc. Does the "Update config files" under the ABM heading in fact do both?

    No doubt many other questions will arise when actually writing something, but perhaps would be better dealt with by PM. If so, to whom?

    EMJB
    Xtrend Xt10000 with 3 Freeview tuners

  6. #5
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    Oops - in my previous post I referred to "SignalFinder" when I meant "FrequencyFinder". I don't seem to be able to edit it - can someone remind me how to do that?

    Edit: An "Edit post" "button" appears at the bottom of this post, but not the previous one!


    EMJB
    Last edited by EMJB; 12-08-18 at 16:30.
    Xtrend Xt10000 with 3 Freeview tuners

  7. #6
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    Quote Originally Posted by EMJB View Post
    Oops - in my previous post I referred to "SignalFinder" when I meant "FrequencyFinder". I don't seem to be able to edit it - can someone remind me how to do that?

    EMJB
    There's a 30 minute limit after posting when you can edit your posts.

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  9. #7
    Moderator Huevos's Avatar

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    Q1, Enable the terrestrial tuner in T2 mode. Region is not relevant to ABM scanning. ABM is the quickest way to achieve this as long as the mast is available in the list and any overrides for T2 are current. If not create a new provider with "DVB-T frequency finder".

    Q2, Signal finder is nothing to do with ABM. Use "DVB-T frequency finder" to create an ABM provider. The new provider persists through config file and OpenViX updates and is also saved by OpenViX backups.

    Q3, If Burnham-on-Crouch is a repeater of Sudbury there would be no bonus in receiving anything from Sudbury. If Burnham-on-Crouch transmitter is not included in ABM list use "DVB-T frequency finder" to create it. I am not going to repeat how in this thread because it is explained in the ABM sticky.

    Q4, No idea. I don't live in the UK. As far as I know COM7 and COM8 is identical across the 4 nations. Local muxes would have different TSIDs. Use "DVB-T frequency finder" to create a provider. The "home transponder" of the provider will be the strongest DVB-T mux. The only TSIDs used to create the bouquet will be the ones listed in the SI tables on that mux.

    Q5, The frequency with the strongest signal for each TsId found. TerrestrialScan does not create anything for ABM. "DVB-T frequency finder" only creates ABM files.

    Q6, A frequency change will only affect ABM if the home transponder changes frequency or one of the T2 muxes changes frequency. Creating a new provider with "DVB-T frequency finder" will cure this. If channel names ever change they will be automatically updated by enigma (unless this feature has been overridden).

    Q7, LCN values are read from the transport stream of the home transponder. As the LCNs come from the transport stream there is no wait for anything.
    Last edited by Huevos; 12-08-18 at 16:44.

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  12. #9
    ViX Beta Tester birdman's Avatar

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    Quote Originally Posted by Huevos View Post
    Q3, If Burnham-on-Crouch is a repeater of Sudbury there would be no bonus in receiving anything from Sudbury.
    It's not a repeater - it's Freeview Light (the PDBx muxes only). Essentially it's a separate transmitter. The Sudbury one transmits COM[456] too.
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    Quote Originally Posted by birdman View Post
    It's not a repeater
    I've got know idea what that means without seeing the transport streams from both masts. Just because a mast does not carry the full range of muxes does not mean it is not a repeater.

    @EMJB, please supply a full set of transport stream recordings from both masts and I will then be able to give you a comprehensive answer to your question.

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    I fear we are getting hung up on terminology that is confusing rather than helping. My understanding/use is that:

    (1) "Freeview Light" is a "trade name" for stations which only transmit the three PSB muxes.

    (2) I have used "Fill-in" to describe stations that are low power (typically <1% of the main stations) and designed to fill small gaps in the main station coverage, such as caused by a town being in a steep-sided valley.

    (3) While most fill-in stations are Freeview Light, and most Freeview Light stations are fill-in, I am not sure that these terms are 100% correlated.

    (4) Burnham-on-Crouch is both fill-in and Freeview Light.

    I did some experiments with the Sudbury and Burnham signals some 18 months ago, and I am fairly sure that they showed that the TsId's were identical for the common muxes, which is a clear indication that everything else is identical. Unfortunately I had a computer failure shortly after so retrieving the those experimental results from back-up in non-trivial. I have a problem repeating the experiments or providing the data Huevos requested in that they require reconfiguration of my aerial system and interruption of TV viewing for my recently disabled wife - something I only want to do once when I feel all the potential questions to be investigated have come to light. Furthermore the original experiments were performed in winter, and an intervening belt of trees could adversely affect reception of the Burnham signals.

    I am not sure what exactly was meant by a "repeater", nor whether the fill-in stations are fed by fibre optic link or by receiving the main station RF signals, changing the carrier frequency, and re-transmitting them - I would have classified the latter as a repeater, but not the former. Either way transmitting the identical data stream will avoid avoid the need for extra digital hardware to create the amended stream.

    EMJB
    Xtrend Xt10000 with 3 Freeview tuners

  15. #12
    Moderator Huevos's Avatar

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    Forget the method (fibre optic, etc).

    A repeater is a subordinate transmission of a mux that is identical to a mux on the main transmitter. Now think how the SI tables work in that event.

    Here is an example.
    On the main transmitter the SI tables say PSB1 is on 482 MHz. PSB1 is on 482 MHz.
    As the SI tables are identical on the subordinate transmission the SI tables on the subordinate transmission also say PSB1 is on 482 MHz. But the reality is PSB1 is transmitted on a different frequency, e.g. 546 MHz. That means the SI tables are wrong on repeaters and need overrides to be included in the providers.xml.

    "DVB-T frequency finder" makes a best attempt to create a provider file with all the correct setting for the repeater.

    "DVB-T frequency finder" can also be used to create a provides file for a main transmitter where the frequency information is wrong for one reason or another.
    Last edited by Huevos; 13-08-18 at 17:25.

  16. #13
    ViX Beta Tester birdman's Avatar

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    Quote Originally Posted by Huevos View Post
    "DVB-T frequency finder" makes a best attempt to create a provider file with all the correct setting for the repeater.

    "DVB-T frequency finder" can also be used to create a provides file for a main transmitter where the frequency information is wrong for one reason or another.
    Can it be used to pick up the frequencies from the repeater whilst also picking up the weaker signals for the additional frequencies from the main transmitter (assuming you can see both)?
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    Moderator Huevos's Avatar

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    Birdman, as already stated "DVB frequency finder" is a tool to make ABM providers files for terrestrial, nothing more.

    The fetching of muxes is done by ABM following ABM logic.
    Last edited by Huevos; 13-08-18 at 19:40.

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    ViX Beta Tester birdman's Avatar

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    Quote Originally Posted by Huevos View Post
    Birdman, as already stated "DVB frequency finder" is a tool to make ABM providers files for terrestrial, nothing more.
    So I'll rephrase the question.
    If I happen to be able to pick up signals for different muxes from different transmitters, can "DVB frequency finder" be used to create an ABM providers file that includes them all (or all the ones I want)?
    And, in that situation, is there anything that could produce a custom terrestrial.xml file containing just the muxes I can see and wish to use?
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