Masthead booster- amp location

Discussion in 'Audio Visual' started by opps, 29 Nov 2021.

  1. opps

    opps

    Joined:
    16 Jun 2006
    Messages:
    5,424
    Thanks Received:
    884
    Location:
    London
    Country:
    United Kingdom
    Hi all. A friend has moved in to a new home.

    I chased and ran three lengths of CT100 up to the loft. I happened to have a spare 4 port splitter (1 in, 3 out and one power bypass output).

    I then noticed that the aerial has a masthead booster (1 in, 1 out). Once I noticed that, I went down to the room with the pre-existing coax (which isn't needed), I then found a 12v amplifier. Prior to finding the amp, I was going to remove that cable. Can I leave that cable and plug it in to the amp? I am guessing (read: hoping) that it will pass the power back up to the masthead booster. The three cables I ran are for wall mounted TVs. I would place the powered amp in the loft but there are no power points up there. I guess, if needed, I could cut the plug off, put it on a fixed fused spur and run it off the lighting circuit.

    With regards to the splitter that I currently have. I put the "powered" old coax on one of the three output ports that isn't the power bypass output. Given the lack of spare ports, I put the nearest (shortest) cable on that one. TBH, I don't know why the splitter has an output that has a bypass in the first place.

    It will be a while until the TVs are installed. Should the above work or do I need to swap out components?

    Thanks in advance
     
  2. Sponsored Links
  3. winston1

    winston1

    Joined:
    11 Jan 2010
    Messages:
    7,343
    Thanks Received:
    572
    Location:
    London
    Country:
    United Kingdom
    CT100 was made by Radex and has been obsolete for many years. Maybe you obtained fake cable.

    What you found is a 12v power supply not an amplifier. Without it the masthead amp won’t work. It must be fed via the power bypass outlet on the splitter. That is what it is there for in answer to your question. You could move the power supply to any TV point as long as you wire that feed through the bypass port. Just ensure any coax outlet plate you use is not an isolated type.
    If you move it to the loft you don’t need a FCU on the lighting circuit. Best feed it via a small plug and socket such as a BS 546 2 or 5amp type.
     
    • Thanks Thanks x 1
  4. Lucid

    Lucid

    Joined:
    10 Sep 2013
    Messages:
    1,811
    Thanks Received:
    1,047
    Location:
    Cheshire
    Country:
    United Kingdom
    The power pass on your 3-way splitter is there precisely for the use with remote power via coax.

    If we presume that the masthead amp is still required, then the 12v power supply needs moving across to one of the new coax cables. That coax then needs to be connected to the power pass socket on your splitter. Once is is, and the power supply I switched on, then the masthead amp should burst in to life as long as the plug end connections have been made up properly. At this point the old coax becomes redundant.

    How old do you believe the aerial to be? Is it still shiny or does it now look a dull grey colour?

    The reason for asking is that the past 30-odd years have seen several step changes in the way TV signals are broadcast, and so depending on when the aerial was installed it could be that any amplification gear that was needed at the time might not be required now. It may even be that with a change to a better-matched aerial that no amp is required at all.

    If you are not an aerial installer then you won't have a proper aerial meter to check the signal levels, so your next best option is to bring a TV to the property and hooking up to the end of the coax in one of the three new TV positions. Test the signal with the system connected with the amp in place. Use the TV manual tuning menu. You need to check strength and quality for each on the muxes being received. Some will be stronger than others, so it's important to find the high and the low values.

    Test the following stations to get all the muxes. Be aware though that some transmitters only broadcast a limited range of muxes referred to as Freeview Lite. Youll notice too that some of tge following are HD channels. The TV you use will need a HD tuner.

    BBC 1 (SD) is on BBC A PSB1
    ITV 1 (SD) is on D3&4 PSB2
    BBC 1 (HD) is on BBC B PSB3
    QVC is on SDN COM4
    Dave is on ARQ A COM5
    QVC Beauty is on ARQ B COM6
    Quest HD is on ARQ C COM7 for the time being until the stations are folded in to the other muxes.

    TV metering falls in to three categories. Tge most useful give a percentage reading for Quality and Strength.

    The middle range give just a bar scale. Use a tape measure to help record the results.

    The least useful just have a basic one-or two-word description something along tge lines of poor, good, excellent or weak, average, strong. In this case if you can muster up a TV with better metering then do so.

    Once you have as many of the readings as possible then repeat the process with the power supply and amp bypassed. This means making a back-to-back connection to the aerial so you'll need a barrel connector.

    If you're still getting maximum for Quality and 60% or more for strength then you can leave the masthead amp disconnected.

    Do the tests and post the results here.
     
  5. opps

    opps

    Joined:
    16 Jun 2006
    Messages:
    5,424
    Thanks Received:
    884
    Location:
    London
    Country:
    United Kingdom
    Thanks for the reply.

    The CT100 was purchased from Toolstation

    https://www.toolstation.com/search?q=ct100

    Loads of firms make and sell it.

    Again, many thanks, after posting my question I did start to wonder if that was the reason for the bypass.


    I thought that the round pin plugs (often used for domestic floor/table lamps) don't have fuses. I haven't checked the power supply to see what it is rated at.
     
  6. opps

    opps

    Joined:
    16 Jun 2006
    Messages:
    5,424
    Thanks Received:
    884
    Location:
    London
    Country:
    United Kingdom
    Thanks for the reply.

    I think the loft aerial and cable are probably 5 to 10 years old (I am guessing though).

    The connectors used were PCT compression fittings.
    The existing cable work was nice and neat. Appropriately clamped, whereas mine is just sitting on the loft insulation. I did use compression fittings though and what is described as CT100.

    I have noticed that some other houses in the area have super high masts. The location is the Brentham estate (Pitshanger Ealing) http://www.brentham.org.uk/

    I am guessing that the power supply is required.

    For clarity- there are now 4 outputs. The original coax and the three that I have fitted. Even though the original coax is not going to be connected to anything, does it degrade the signal just by being connected to the splitter? If yes, I can cut one of the new coax cables in the loft and move the power supply up to the loft.

    It will be another couple of weeks before the TVs go up on the walls so I will report back then. I do have proper tv signal testing equipment but I will test with the power supply on and off.

    Cheers.
     
    • Thanks Thanks x 1
  7. winston1

    winston1

    Joined:
    11 Jan 2010
    Messages:
    7,343
    Thanks Received:
    572
    Location:
    London
    Country:
    United Kingdom
    They are all lying then. CT100, as I said, was made by Radex only. All these firms are selling copies (fakes).
     
  8. opps

    opps

    Joined:
    16 Jun 2006
    Messages:
    5,424
    Thanks Received:
    884
    Location:
    London
    Country:
    United Kingdom
    After looking in to it I did come across other people saying the same thing. I can only imagine that the copyright/patent expired or that it has become a generic term. There are a number of large firms making the stuff.

    To be honest, I do not know enough about the specification to comment further.
     
  9. Lucid

    Lucid

    Joined:
    10 Sep 2013
    Messages:
    1,811
    Thanks Received:
    1,047
    Location:
    Cheshire
    Country:
    United Kingdom
    That extra info is useful.

    London isn't my home turf, so an aerial installer with some local knowledge will always have an advantage over someone looking at online maps, but from the info I can see it looks like your strongest local transmitter is Crystal Palace about 12 miles away. It transmits at up to 200,000 Watts. That's at the top end of transmitter powers for the UK.

    Where you're located appears to be in a region behind the high ground at Hanger Hill Park / Fox Wood / St. Augustine's Abbey. That probably explains part of the reason for some houses having tall aerial masts. Other reasons include local features such as the height of buildings and stands of trees. The current house aerial is inside the loft. That can knock anything from 3 to 6dB off the reception; 3dB is a halving of the received signal level. 6dB means the signal level is down by three quarters.

    Some of these losses can be offset a little with the right choice of aerial. IFAIK, until very recently Crystal Palace has been classed as a transmitter in the group A band. That meant that its RF channels were bunched in the lower half of the old ch21-68 range. For digital TV that meant the Crystal Palace RF channels used to be between ch22 and ch34. Things changed a bit though because of the need to juggle the other overlapping transmitters because of the sell off for 4G and 5G mobile telecoms. If the info from Wikipedia is correct, CP now broadcasts on the following:

    CP.jpg

    I mentioned Group A transmitters. Aerials matched to Group A transmitters have a red end-cap on the boom. Ordinary Wideband aerials have a black end-cap.

    The advantage with a Group aerial is that all the reception power is concentrated in to a narrow band. If you have a look and compare the black line (W) for wideband to the red line (A) for Group A aerials you can see the peak is higher for red whereas it's lower for black. Also, the whole red curve is in the lower half of the graph, so the reception is concentrated there rather than spread all the way across the frequency range.

    Something to bear in mind is that these are graph curves for top performing aerials. A Wideband High Gain purchased from a non-specialist supplier may well sit lower on the graph because the aerial has less gain overall.

    grouped.jpg


    For Group A aerials their reception range is optimised for ch22 to ch37. That matches well with Crystal Palace except for COM7 on RF ch 55. However, this was only ever intended to be a temporary location. The channels on COM7 were to be folded in to the other muxes. That's still the intention. COM7 on RF ch55 will disappear at some point. You see, the long term plan is to have the TV band go from 21 to 49.

    You can get a bit more info on Group aerials and the differences between mediocre and decent aerials at Wideband / grouped TV aerials - A.T.V. Poles, Brackets, Clamps & Aerials (aerialsandtv.com) It's an excellent site and the guys really know what they're doing. The gear they sell isn't available at the usual retail and DIY stores, so it's worth spending some time on their site then purchasing from them if something new is required.

    Where the aerial in the loft is an ordinary wideband then changing to a good Group A aerial might help provide a healthier signal before amplification.

    Regarding the cable, there's a lot of firms selling "an equivalent to CT100" which then gets shortened to CT100. Webro, a firm I have a lot of faith in for cables, even sells a direct CT100. It's not the same spec as their WF100, but if it's already in then there's no point losing sleep over it. https://www.webro.com/tv-satellite/ct100-cable/

    If any of the posts here have helped you, then hit the THANKS button. It's a nice way to show your appreciation for the time and expertise someone has given to help you.
     
    • Thanks Thanks x 1
    • Like Like x 1
  10. Sponsored Links
  11. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    9,762
    Thanks Received:
    1,320
    Country:
    United Kingdom
    Strictly speaking, each unused output or cable end which is plugged in - should be terminated with a 75 Ohm terminator. These are easy to make, by soldering a 75 Ohm resistor between inner and outer of a plug.
     
    • Thanks Thanks x 1
  12. winston1

    winston1

    Joined:
    11 Jan 2010
    Messages:
    7,343
    Thanks Received:
    572
    Location:
    London
    Country:
    United Kingdom
    Like all the other companies claiming to sell CT 100 that Webro stuff is fake. CT 100 cable used copper braid not copper clad aluminium.
     
  13. opps

    opps

    Joined:
    16 Jun 2006
    Messages:
    5,424
    Thanks Received:
    884
    Location:
    London
    Country:
    United Kingdom
    Thank you for the comprehensive reply. I will try to focus on it when it is time to put up the TVs.
     
  14. opps

    opps

    Joined:
    16 Jun 2006
    Messages:
    5,424
    Thanks Received:
    884
    Location:
    London
    Country:
    United Kingdom
  15. Lucid

    Lucid

    Joined:
    10 Sep 2013
    Messages:
    1,811
    Thanks Received:
    1,047
    Location:
    Cheshire
    Country:
    United Kingdom
    Opinions differ on terminators. Some say they're required, others say you only really need to terminate the full power output of an amplified splitter if the unit has one. This latter is my opinion too.

    There's no harm terminating any unused outputs; it won't break anything. I'm just dubious about any significant benefits, so I would question whether it's really necessary. The standard outputs from an aerial amp have enough isolation from each other that any signal reflections from an undermined output won't affect the other outputs.
     
    • Thanks Thanks x 1
  16. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    9,762
    Thanks Received:
    1,320
    Country:
    United Kingdom
    The proper termination is supposed to help prevent the signal bouncing back, in anti-phase to the needed signal. I have an eight way distribution amp, with only five outlets in use, one of the five to the front bedroom uses old coax which I should have replaced with CT100, but never got around to it. It's also the longest run of coax. The signal there was slightly marginal at times - so I thought, for the sake of a few pence, to try adding terminators to the three unused outputs several months ago. Since then the front bedroom signal quality has increased and the TV has not had a problem.

    So I would suggest that in marginal situations, they can help.
     
  17. Lucid

    Lucid

    Joined:
    10 Sep 2013
    Messages:
    1,811
    Thanks Received:
    1,047
    Location:
    Cheshire
    Country:
    United Kingdom
    Thanks, and yes I know what it does. I think it's a bigger problem for signals travelling down a particular line if there's an impedance mismatch; less so for the signals on adjacent outputs. That was the point about mentioning the isolation between the outputs.

    There'll always be a small number of cases where the signal is marginal, and so if 0.5~1.5dB helps lift is just enough to clear the digital cliff then it will look like a cure. Can't argue with that, and like I said before, adding terminators won't break anything. I carry some in the van so I'm not averse to using them if the situation calls for it.

    My approach though would be to fix the low signal level issue properly rather than trying to patch it. Getting a signal to just scrape past the lower signal threshold still leaves it vulnerable to loss, but I'm approaching this from the point of view as an installer rather than as a homeowner just trying to get something to work tolerably.

    As I said before, terminators won't break anything, but I'll add that their efficacy is limited and is also dependent on frequency. To put them in to context, changing from a crappy Pound shop coax fly lead to a bit of decent coax will have a bit more benefit. This is because it will lower the noise floor as well as reducing the resistance.
     
    • Like Like x 3
Loading...

Share This Page