Multi tv points in a nursing home

destix

Standard Member
hi
looking for a little advice
been asked to upgrade tv system in a nursing home, i cover full electrical/fire alarm/nurse call, building maintenance etc etc for alot of nursing homes

they were unable to recieve freeview with the existing grid array aerial , so i changed this to a DAT HD/45 , which upon direct connection to 1 tv gave a very good signal
the problem is that from the aerial it is connected in the loft to a very thick coax , this serves as a back bone and passes in and out of 12 connection boxes throughout the loft
each box has a passive splitter with an in/out for the large coax , and 4 outputs for 4 rooms
this is causing the signal to drop below acceptable level across all 48 points
receiving 3 out of 6 muxes
my plan is to order 12 x 4 way amplifiers with the large coax feeding all the inputs to the amps
anyone think this is a good solution?
my previous experience in these nursing homes has been all cables wired to 1 or 2 locations with 24 way etc amplifiers
but this home has been wired in 12 groups of 4 cables and im not sure about connecting so many amplifiers
thanks for any help :)
 

Rodders53

Distinguished Member
Has DSO happened yet (I guess not)? When will it? Is a wideband aerial correct for the transmitter? NB There will be a 10x (10dB) power increase - usually - at DSO, which needs to be considered in your design.

You really need professional equipment to measure RF signal levels and also do gain/loss calcs for the cabling and splitters present. (They sound more like 'taps' than splitters from your description, though --- any makers or model numbers on them?).

If the system works well for analogue - use Ceefax/Teletext p 284 on receivers in each room to assess if the system is expected to be adequate or not for digital after DSO. Any existing analogue signals might overload amps - or not - measurements would help ..... a 'launch' amp may be all that is needed retaining the passive splitting or tap-off arrangement.
 
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destix

Standard Member
Hi
Yes I think your right , they are probably wolsey tap off units
As when I put my dvb-t Meter onthe in/out it gave full signal , but on the outputs it barely gave 1 light , is the signal being reduced too much by these taps?
I should have mentioned I do have 1 telves amp powering the mrd with a variable gain for the large coax backbone cable
 

Rodders53

Distinguished Member
I've highlighted the most relevant line and you need to measure each of the analogue and digital signals present, separately - that is four/five analogue frequencies and six or seven digital (depending on location) - unless you do all of them simultaneously via a spectrum analyser display.

I don't know how these cheap led signal finder meters work - I suspect they are just some sort of average of all signals received in the 21-68 band? http://www.caravanclub.co.uk/media/4444599/buycomparison.pdf reviewed a few for touring caravanner's use. That article implies to me that most are rather insensitive and only work well in strong signal areas.

My understanding of the design of a tap-off system is that you start with 100 units at the antenna/first tap - you need 70 (say) to each dwelling so the 1st tap drops 30.... at the next tap the signal is 90 so tap2 drops 20 and so on.... only when the input gets near to 70 (due to losses in the cable) do you need to amplify.

Wright's Aerials has some interesting articles.

Knowing where the home is situated and what transmitter is being received might allow us to judge likely relative signal strengths. The local Post Office or Pub postcode is usually adequate.
 
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destix

Standard Member
yes been reading a bit about taps etc , i understand the system now
the problem is , even at the first tap which was a metre from the televes launch amp , the signal on my crude meter was full on the input but flickering on 50dbuv on the 4 outputs
the rating of the taps seem to be a bit heavy handed
would replacing them with variable 4 way amps not work?
turn the amps down to the lowest setting and work from there?
Antiference a240lr for example
i realize i should ideally be working with a spectrum analyzer but that will prove to be next to impossible to get my boss to cough up for :rolleyes:
 

Rodders53

Distinguished Member
i realize i should ideally be working with a spectrum analyzer but that will prove to be next to impossible to get my boss to cough up for :rolleyes:
Hire a meter on analyser? Or get the boss to pay a professional aerial man with one to advise? How's he able to guarantee the work if it's effectively an amateur installation? :lesson:

This HDTM Plus Professional Terrestrial DVBT Meter Free Delivery : Aerial Signal Strength Meters : Maplin might help (and should be cheaper elsewhere) - but it won't do DVB-T2 (HD), of course.

What rating are each of the 12 taps? The nearest will have the most attenuation... and the pass-through to the next will lose a dB or so...

You don't say if the analogue reception is good or poor in all the rooms.

Are there any other boxes - channelised filters for example - in the system that may be affecting the DTT signals?

I need the location/transmitter info to give useful advice on switchover and relative signal levels now / then.

IF you decide to go down a splitter-DA route you'd need to rewire completely (IMHO) to 'lose' the backbone-tap cable. (You'd still need to do design gain/loss calcs). It's never a good idea to cascade amplifiers and 12 in series would be bound to lead to carrier/noise issues. :lesson: Amplifiers are also much less reliable than passive devices, far less 'green' wrt energy consumption, and a potential fire risk.
 

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