Attention TV antenna Gurus... HELP!

[biggeorge]

I am working on a job at the moment where there are 14 tv's wired into a rack full of assorted tv feeding gear in a hotel. Such as DVD players, sat boxes, tv antenna, etc...

I'm pretty savvy with this stuff but never approached anything on this scale.

Anyhow, I am in the process of tracking down a few problems with the setup, and I have most of it sussed out, but I have never come across a splitter with a "TAP" label on it.

There are splits off splits and splits off splits with some taps going here there and everywhere, If I were a tv signal I wouldn't know which way to go, coz it looks to me like the system has just been added to by various "idiots" over the years, and it's come to a point where the whole lot is clashing.

Can someone please explain what a TAP connection does in the circuit, and I need to know how it is used and every which way it can be used. Point me to some examples if you wish.

I am dealing with junk like 1-2 splits that go to 2-1 splits back into 1 cable.
There is a frequency shifter module installed as well, so we're getting channels like 7,9,10 on 7,9,10 as well as 31,35,37 and 42, 46, 48... Stupid shit like that.


Thanks in advance.

[Fernbay]

IF you have a large MATV system, you amp the signal first.
If that signal was sent to a TV, it would overmodulate, causing interferance.
Amping would be nessesary due to the long cable runs and multiple outlets.
The further you go, the more signal loss you will have.
The aim is to have a good signal, of say 65db on all outlets.
After the Distribution Amp (the DA), the signal might be about 95DB
Taps will drop about 2db across them (from in to out) & attenuate the signal on the tap acording to it's specs.
In the case of this example, the first tap would need to be 30db to drop the signal to 65db
At the other end, after 100M of cable & various taps, you may not need to attenuate the much at all, maybe only 6db

Another reason to use taps, is because they isolate the outlet.
If someone shorts the outlet for example, it won't effect the rest of the system.

So, when planing your system, you would meter the signal, then figure out the cable loss acording to it's specs and balance the load around the system useing taps.

Does that make any scence?

[Antennaman]

I'm pretty savvy with this stuff but never approached anything on this scale.

I will compliment you for admitting to that.

Having installed and fixed many sytems like this, it is the ones added to on an ad-hoc basis that are usually the worst as you are finding.

In some cases it may be necessary to completely re-design or re-jig the system, particularly when, as it would seem in your case, frequency translation components and channel filtering are being utilised.

The first thing to do is draw up a plan of the system, unless you are lucky enough to access this information from somewhere else. This will enable calculation of system levels so that your final testing will have some relevance.

Taps are used to ensure that signal levels for all the outlets in the system are within a small tolerance band for all the required channels that can be received at these outlets. In simplest terms they are a type of splitter that has a predetermined loss to achieve this balance.

There are a number of Australian Standards that apply to these types of installations which are relevant and should be referred to. If any of this stuff is Foxtel or Austar, they also have inhouse requirements for installations to adhere to.


I wish you sucess with your endeavours, and remember that in evolution, systems tend to develop up to their limit of adaptive competence.

[biggeorge]

I'll do my best to explain what I remember here.

TV antenna comes in from roof, goes thru an amp and into a IN port on a combiner. Same combiner also has a TAP input which is connected to a 8x rack of RF sat boxes (which are on a 8x multiswitch, all seemingly working correctly). The OUT port of the combiner goes to another amp which then runs out into a freq shift device (apparantly connected back to front!??!?) and into a 2 way split.

1 port off the split runs to a room (Couldn't see the tv due to room being occupied), the other runs to a 3 way TAP.
Port 1 off the TAP runs to a 4 way split and goes to 4 rooms.
Port 2 off the TAP runs to another 2 way split/Tap which runs to a 5 way split and runs to 5 rooms.
Port 3 off the TAP runs to a 4 way split and feeds 4 rooms.

Yes, I committed all that to memory....

I have no idea of the attenuation of the TAPs, it is not marked on them and I did not have signal meter with me, yesterday's task was to have a peek at the mess and try and determine why they were getting interference on EVERY channel.

After sussing around a bit I turned the UHF dial right down on the 2nd amp and cleared up the austar RF feeds to about 90% satisfactory picture but I still have FTA clashing with something, 7 was ghosting bad, 9 was ghosting and had a purple band vertically 1/3 from the left, and ch10 cleared up nicely after I turned the UHF down.

I tried removing amp #2 and bypassing it but lost all FTA, but austar got as good as RF could get.

I am not happy running the combined austar thru amp#2 via the TAP port, it makes no sense to me...

Also this split off tap business seems absurd to me. I'd rather 1x 16 way split, cap 2 off. Or run a 2x split into 2 8x splits to feed the lot the same amount of signal.
Cable runs do not vary THAT much, but I know I lose 0.2dB per metre. Each outlet couldn't be more than 10-15m from the rack.

[aaeon.1]

if the idea of taps seem absurb to you dont start messing with hotels then
as that the only way it should be done
by using taps its more than possible to get more than 100 outlets working in a hotel all at 68db on one dw 40 amplifier

[biggeorge]

I think I worded that wrong aaeon.

The thing that was most absurd was that the rooms with the longest cable runs were the ones at the end of the chain of taps, the shortest runs were closer to the 2nd amp. But since the rooms have a similar cable run then I feel justified calling it absurd when there is one tv hooked up to the first splitter in the chain, and the room next door is hooked up to the last Tap in the chain and has a shit picture.

I didn't have much time to really get into it, but it was done very badly and there were problems that would be quite simple to iron out if I put in the time to suss it all out properly.

Do any of you guys have any examples of such a setup I could take a peek at, even a wiring diagram of a past job you've done or some happy snaps... ?

[trash]

This distribution system doesn't sound so unusal to me, but maybe I'm used to designing and building these sort of logical systems.

There are some very simple rules that will help you understand the network structure.

The first is the signal strength should be THE SAME at every socket.
This might sound impossible, but it is quite simple. It requires the use of taps rather than spliters, or using symetrical network structure which aren't as cheap or efficient.

You may be familiar with splitters and combiners. A splitter with 2 ports is easiest to understand. Signal input on one port, and the same signal on both outputs. The same signal power (half power) appears at the outputs. The inherent signal insertion loss is -3dB.
Expand this to 4 output ports. Each output signal will be one quarter of the input power or -6dB insertion loss.
Expand this to 10 output ports. The insertion loss is now -10dB on each port.
(Ten times less power).

A tap (a directional coupler) does not work like a spliter. In common terms it works a bit more like a bus stop. Some of the passangers get off while most continue on.

A 10dB directional coupler (10dB tap) will have an input, and output and 'the tap'. Most of the input signal will appear at the output 9/10ths, will one tenth of the signal will appear at the tap. (-10db)

Now if we consider a hotel with 100 rooms. In ten block of ten rooms.
If we use one splitters, then either we need to use lots of cable to create a fractal network using spliters. If we use 10 port spliters, then the inherent loss of the splitter network is -20dB and three times the cable is required with three times cable insertion loss.
If we use 2 port splitters, then the inherent loss of the splitter network is -21dB with lots of coax.
These networks need to be symetrical else the end rooms will have up to -300dB insertion loss.

A simpler network is to use a trunk cable with a backbone of direction coupler taps which then feed splitters.

If we run the trunk cable past all ten blocks and have a tap at each, we can then use that tap to feed a 10 way splitter and run a short length of coax to each room. Inherent loss is still -20dB but using a lot less coax.

A good example of these networks is cable TV street cables. The trunk runs down the street and at each power pole is a distribution box which contains a directional coupler with something like a 10 port splitter. Aerial cables are then run out to each house from each power pole. Unused ports are terminated with dummy loads.


The other rule is there will be a point where all signals pass through.
The network takes on a true tree structure. All the outputs are the leaves on the various branches. Or in a network using taps, rather like a grape vine.
There can only ever be one trunk.
The network input may be sourced from multiple devices, like the root system, all these inputs need to be combined to feed the trunk.
If different sources have the same frequency on the trunk, then some of them need to be moved to vacant frequencies or excess channels blocked.


If you're trying to reverse engineer a complex network... apply the rules and draw it out on paper. Number the ports, calculate the insertion loss of the various splitters and directional couplers and you should have a good idea of exactly what is going on and how to manipulate it to do exactly what you need.

[Fernbay]

I was trying to say something like that!
Thats a fantastic summary Trash

[BillyGoat]

Well done Trash, that was easy to understand.
Thanks.

[custom]

Trash - very nicely put, I will forever now use the Busstop analogy. I have read this late and would love to know how you went Bigeorge. The system does sound reasonable,apart from some co-channel interference you may be getting. cheers

[MrElectricity]

The quickest answer is the Clipsal rep in our area, he and his mate that specialises in data and TV are very knowledgeable and would be available to meet on site, sort it and of cause suggest there products, splitters compression fittings etc. PM or call me some time and I will text ya the phone number.

[rickove]

yeh dont be shy bigG,get some local rep help,quick!,save the Headache?as mr Electricity suggest.
Keyboard Junkie solutions arent always the $$$ an time solution.for real time !

[biggeorge]

I haven't been back there yet.

One thing I did omit was that TV antenna was broken, it had a few rods missing off the back end where the largest ones are.

When I go back there I might start by replacing the antenna and go from there.
Thinking about it now though, I really think the problem is that the owner of the place is a stingy coot and keeps getting in amateurs who add bits, swap cables, dick around with stuff they don't understand and probably don't get paid for it or paid very well. Over time there has been so much thrown into the mix and put out of whack that the system is fighting with it'self doubling up on some channels and blasting signals over the top of others.

Not so sure if I want to go back there.....

[MrElectricity]

Clipsal Rep for Western Sydney great guy called Tyson used to be a Sparky in the Navy. Don't know if I can post his contact number here.