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Wired TV RF distribution question

Discussion in 'General Electronics' started by TheMekon, Aug 27, 2007.

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  1. TheMekon

    TheMekon Guest

    Not sure if this is the right forum but here goes....


    I need to distribute off-air TV round a client's premises to about 20
    outlets as RF
    Easy, I get my friendly aerial man to do a distribution amplifier etc.

    (I am in the UK and we are talking about PAL system I)

    But...

    Client also needs 6 channels of locally sourced video mixed in with the
    distribution.
    If it was 1 or 2 channels I would just get cheap modulators, choose a
    couple of blank channels and mix it in with the off-air feed.
    But doing 6 channels worries me.
    Do I need to worry about the performance of cheap modulators?
    Do I need to worry about intermodulation problems?
    What else do I need to worry about?

    Thanks!
     
  2. Marky P

    Marky P Guest

    Hmmm. I'm not THE expert on here, but let's see... Where abouts in
    the country will this installation be? You need to find out all the
    frequencies used for analogue & digital TV that cover your clients
    area THEN find out if there a six spare ones. It's possible, but
    sounds like a bit of a sod.

    Marky P.
     
  3. You Haven't a chance in hell of getting that number of channels to work
    well. They'll work after a fashion, though.
     
  4. tony sayer

    tony sayer Guest

    Yes it will work, you just need the right equipment.

    Look up Taylor transmitters in Oldham they do this sort of stuff and
    sell it everyday!. A combination of modulators and channel filters is
    what's required.

    Bill W could no doubt give you chapter and verse on this subject...
     
  5. charles

    charles Guest

    I think you'll have to keep out all stray ones. That means using
    channelised filters on the input. Then you should have reasonably clear
    space to add your 6 new ones. Remember to avoid n+5 and n+9, although the
    latter doesn't affect modern sets. ('n' being wanted channels)
     
  6. Ivor Jones

    Ivor Jones Guest

    [snip]

    : : Yes it will work, you just need the right equipment.
    : :
    : : Look up Taylor transmitters in Oldham they do this
    : : sort of stuff and sell it everyday!. A combination of
    : : modulators and channel filters is what's required.
    : :
    : : Bill W could no doubt give you chapter and verse on
    : : this subject... --
    : : Tony Sayer

    I have 6 "extra" channels distributed around the house (2 x DVD recorders,
    2 x VHS recorders, 2 Freeview boxes) and it works, but there's not a lot
    of space between some of them..!

    I'm in the Midlands and receive from Sutton Coldfield (Lichfield for Ch.5)
    and the channel numbers used are as follows:

    22 - Freeview 1
    26 - Freeview 2
    31 - VCR 1

    37 - Ch 5
    40 - BBC2
    43 - ITV1
    46 - BBC1
    50 - Ch 4

    60 - DVD 1
    65 - DVD 2
    68 - VCR 2


    Ivor
     
  7. I've yet to see one work what I'd consider perfectly. And I've seen plenty
    of RF distribution systems in studio complexes. Where I assume cost
    doesn't matter.
     
  8. Bill Wright

    Bill Wright Guest


    This is what we do. It's our mainstream business.

    See:

    http://www.wrightsaerials.tv/SystemPlan.htm

    http://www.wrightsaerials.tv/Main Services/System Planning/example of working drawing 2.pdf

    http://www.wrightsaerials.tv/410boxesthreeandfour.htm

    Contact me via the website if you think we can do business.

    Bill
     
  9. charles

    charles Guest

    but, if you've seen them in BBC studio complexes, consider how many Studio
    Capital Projects people knew anything about RF. Mike Lyons did - in the
    end.
     
  10. Bill Wright

    Bill Wright Guest

    Some of the worst RF botchery I've ever seen was in studios and news centres
    and such like places.

    Bill
     
  11. Bill Wright

    Bill Wright Guest

    Well, I'm sorry, but you're wrong. There's no great difficulty in getting
    excellent results from multichannel RF systems if you know what you're
    doing. We do it every day. It isn't magic and it isn't rocket science.

    We have customers who demand perfection, and they get it.

    My own household/workshop system carries ten in-house channels, seven
    off-air analogue and six off-air muxes and believe me I won't tolerate
    anything less than perfect reception.

    I know what's made you believe that it can't be done. You just never seen it
    done properly so you've quite reasonably reached a (specious) general
    conclusion.

    Some of the worst systems I've seen have been in studio complexes. I could
    name names . . .

    Bill
     
  12. charles

    charles Guest

    It doesn't surprise me at all. In Manchester you could watch the output of
    the continuity studio in the road outside on a tv set. Talk about 'leaky
    feeders'.
     
  13. Mike J

    Mike J Guest

    Ah a name to remember - re-built London Switching Centre as well!!

    Mike
     
  14. Graham.

    Graham. Guest

    The MDS was reasonably well engineered when it was first installed
    (in-house) in the mid 80s

    Before that there was a Top Rank twisted-pair system (vision carrier
    a little higher than Redifusion IIRC) feeding 22in Doric monitors.
     
  15. Alan White

    Alan White Guest

    Mike was the Project Engineer for the video installation assisted by
    Mike Turner and Keith Sudel. I was the Project Engineer for the audio,
    comms and switching installation assisted by Dave Daborn and Graham (?).

    I think it was the second time that we'd used a
    modular system of desk construction, the first being in Belfast CTA in
    the late 60s. Prior to that, every desk panel was custom made for its
    application. This was expensive and inefficient in terms of
    Engineer/Draughtsman time and effort. Another Engineer, Denis Noble,
    who worked for me on the Belfast CTA project, and I decided to go for
    a set of standard modules which could be fitted into a desk to fulfil
    the operational requirement. We used ISEP frames and modules, decided
    that BBC ED24 grey was not a good colour in subdued lighting so went
    for a dark green (068 in BS2660?) with yellow engraving, round push
    buttons for executive functions, square buttons for non-executive and
    the cabling to every panel had to be long enough to allow that panel
    to be positioned anywhere in the desk. Roger Jephcott, who was the
    Ops. Manager(?) requested a rearrangement one week before the service
    date which was very easily accomplished. That would have been
    impossible using the old construction method.

    I can't remember what we used for the audio matrix but it was probably
    Type 25 miniature relays which were in widespread use by then and had
    replaced the PO 3000 in most applications. The video matrix would have
    been a DD effort. One anomaly, which we had to overcome everywhere
    with a married audio/video matrix, was that DD, in their wisdom had
    wired the control inputs to the video matrix in terms of the
    destinations and our audio matrix was wired in terms of the sources.
    This was sorted out on PO tag blocks with the control cables from the
    audio matrix being wired to the column tags and the control wires to
    the video matrix being wired to the row tags (or the other way round).

    Dave Daborn did a brilliant job on this desk. I think it was the most
    successful desk that we'd installed up to that time and, probably,
    since. Certainly there was a great deal of discussion about the layout
    and the fact that it was built virtually in situ helped a lot.
     
  16. Mike J

    Mike J Guest

    You mean like this Alan?

    http://www.bostonmanor.plus.com/SWC_Main_Desk.jpg

    and stories like this:-

    http://www.bostonmanor.plus.com/ExBHComms/SWC.html

    The previous re-build was after the first DD solid state matrix came in.
    Controlled by 24way yaxley switches with a centre extra concentric
    switch to select 1-24 + 25 (P&B) as no-one made 25way break before make
    switches!!
    That was after the first matrix install which was controlled from the
    25way Ledex switches via the old video switching level as the other
    levels were still in use for audio and 'marking'

    Mike
    (SWC 1969ish and sometime supervisor)
     
  17. Bill Wright

    Bill Wright Guest

    I've told the story on here before of the housing estate that got satellite
    telly from their aerials, thanks to the news facility over the road.

    Bill
     
  18. Alan White

    Alan White Guest

    I remember the Ledex switches, which always struck me as being
    incredibly crude. Didn't they come four to a box (or am I thinking of
    something else) and were very noisy?

    Andy Hame posted this link about eighteen months ago when this topic
    came up,
    www.acdale.plus.com/PeteT/LO_SWC_Desk.html which shows the desk in all
    its glory.

    Thanks very much indeed for your link. It all seems so long ago now but
    then I suppose it was.

    Mike Lyons and I did a lot together including rebuilding Cardiff
    Broadway Switching Centre, my first 'big' job, Belfast Central Technical
    Area, London SWC, and Glasgow Switching Centre. Happy days!

    Thanks again, that was good.
     
  19. tony sayer

    tony sayer Guest

    Suppose they were either SCPD or TCPD ;)...


    There wasn't a RCPD was there?...
     

  20. Not as I recall.


    SCPD = Studio capital projects department, possibly now part of Siemens.

    TCPD = Transmitter capital projects department is now a division in
    the Warwick based company called National Grid Wireless, was at Henry
    Wood house.

    RD = Research Department at Kingswood Warren.
    DD = Designs Department at Western House
    ED = Equipment Department in Chiswick.

    These three merged to form BBC R&D based at Kingswood Warren in Surrey.


    There were other sections such as Transmitter group, Engineering
    information Department, Communications Department ect.

    Much of it merged, such as TCPD and Transmitter group merged to form
    BBC Transmission.

    Jim
     
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