Distribution Or Masthead

[rmalpas]

I am a comms cabler who has for over a year now been installing Digital antenna's, I must admit compared to data cabling Digital TV antenna installation and subsequent cabling catering for signal loss and signal quality is a magnitude more complex that data cabling.

I have been wondering about the best way to provide distribution amplification in two situations and would appreciate all help and comment.

Firstly I accept that after exhausting all avenues of improving signal strength through antenna location and selection assuming BER levels are acceptable then a masthead amplifier should be used to correct low signal strength . Also that if the user wants multiple outlets and antenna signal is all ok then generally a distribution amplifier especially if a unit with multiple in biult outlets is useed is a good solution. But what should the preference be when

1/ You need to boost the signal at the masthead, and then provide output to 3-6 walloulets.

AND

2/ when the masthead signal is fine but the customer wants 5 or 6 outlets.

In 1/ Should you simply turn the gain up on the masthead amp and use a splitter or splitters to split the signal ensuring all outlets end up with a final signal within acceptable BER and strength tolerances INSTERAD OF keeping masthead amplification moderate and adding a distribution amp. I would opt for the former as I would expect mutliple amplifiers will simply lead to further BER degredation. Comments???

In 2/ It would seem obvious ( I am often wrong) a suitable distribution amplifier should be used ahead of the splitters, still focussing on achieving balanced signal strength and acceptable BER at each outlet.

I see so many systems where antenna signal is fine but a masthead amp has been used because the customer has 4-6 outlets and its what the installer seems to have at hand and its often cheaper than a decent distribution amplifier.

I appreciate all feedback and technical comment, I am only to happy to learn...

Thanks in advance

Ray

[bellotv]

Hi rmalpas

As you probably are aware ,every install is different in its own way so general rules are hard to apply.

Distribution amps generally require 230Vac to operate and as you said are required prior to splitting which normally is the ceiling cavity of most residences.

This is generally not practical for several reasons .

1) ceilings are stinken hot locations and amps tend to "cook" up there and

2) Its highly unlikely there is a 230v socket up there in an appropriate position

3) The distance from the antenna to the amp is negligible.

My preference is to use a masthead amp where possable. As long as the maximum levels (channel de-ratings) are not exceeded. My logic

Best S/N straight off the antenna

Highest signal in cable to overcome any impulse noise.

Masthead amps have better noise figures than Distribution amps

Mastheads last longer in outside cooling and sparkie not needed to fit power point in ceiling.

I agree that there are a lot of installs out there with TOO HIGH GAIN masthead amps fitted.

I tend to aim for a outlet level of around 60dBuV and calculate back what gain I need to achieve this .If the end result is 70-75dBuV at outlet then I'm happy with that but no more.

But you need to see what else is there as well.Its fine having 70dBuV at the outlet on all digital channels but not if there is 95dBuV of something else that is not needed.

I think there is a need for a low gain masthead 12-16dB SINGLE OUTPUT .There are low gain types with multiple outputs which don't quite fit the bill and there are the MDA series (Kingray) but even these are a bit high in some cases and are relatively expensive.

Having said that I do use distribution amps as well

Edited May 3, 2011 by bellotv

[alanh]

rmalpas,

Kingray Masthead distribution amplifier MDA20H for band 3 - 5 or Kingray MDA20U for band 4-5 only. They use a plug pack and use the antenna cable to conduct the power via the the splitters to the amplifier which is mounted 1 m under the antenna. Remember the plug pack inserter must be in the power pass output of the splitter(s).

Using a digital field strength meter the appropriate gain antenna or an attenuator can be used adjust the signal levels to prevent intermodulation products from being a problem.

AlanH

[I am not a duck]

G'day rmalpas,

I install in a regional area that uses band 4/5 UHF transmissions, utilising masthead amplifiers in about half of these.

My comments relate to domestic situations only.

I prefer masthead amplifiers for reasons bellotv has mentioned, although I note some distribution amplifiers have low noise figures now as well.

I also carry a couple of distribution amplifiers, usually to replace already installed ones that have failed.

The premises may have from 1 to 12 TV points, and as masthead amplifiers are available with gains of from 10dB, to over 40dB, this makes selection of one that will give from 60-75 dbµV at the outlet simple.

I've also cascaded masthead amplifiers (or masthead and a distribution amplifier) to get a combined gain of up to 58dB, to achieve this end.

I generally aim to not have to use the gain adjustment of the amplifier if possible. It means carrying a few different types of mastheads, they don't take up much space.

I also use dc plug paks with transformer/rectifier/capacitor technology, as distinct from the switch mode ones that are getting around now, for reliability purposes.

Splitting is done with (mostly) all port power pass diode controlled splitters, to enable the customer to move the power injector to a more convenient position, should they desire to rearrange their furniture at some time. I do occasionally use drop taps, and generally aim for these to feed points where you wouldn't normally put a plug pak, eg bedrooms, under utilised areas etc.

If the antenna is on a mast, then I place the amplifier at a convenient point to reach, to make future replacement easy.

Antennas are available with pre-amplifiers as an accessory that fit in the balun housing, however, I no longer use these, as I've found reliability issues with them.

bellotv's point about examining the whole spectrum of frequencies in use is important, to ensure high level unwanted signals are not present.

In theory, the C/N ratio of the amplified signal should only deteriorate by the noise figure of the amplifier, so using amplifiers with the lowest noise figure would be the way to go.

Good to see you are learning by doing, experience is the best teacher imo.

Marc.

Edit: context.

Edited May 3, 2011 by M'bozo

[rmalpas]

Many thanks for all that it seems I have been on the right track the fact that the larger dist amps require 230V was one that I had wondered about .

Last question who can supply notched amplifiers to use where one frequency is providing a significantly lower signal strength figure that all others, likewise for a supplier of nocthed attenuators I have asked my usual suppliers (Middys and Radio Parts) and they just give me a strange look and have no idea.

Many thanks to all for the comments.

[mtv]

Many thanks for all that it seems I have been on the right track the fact that the larger dist amps require 230V was one that I had wondered about .

Last question who can supply notched amplifiers to use where one frequency is providing a significantly lower signal strength figure that all others, likewise for a supplier of nocthed attenuators I have asked my usual suppliers (Middys and Radio Parts) and they just give me a strange look and have no idea.

Many thanks to all for the comments.

You can get remotely-powered distribution amps, but as you say, the higher-powered versions are designed to be installed in an enclosure, etc, with mains power available.

For filters, etc... specialist TV distribution equipment suppliers, including Lacey's TV www.laceys.tv

[rmalpas]

You can get remotely-powered distribution amps, but as you say, the higher-powered versions are designed to be installed in an enclosure, etc, with mains power available.

For filters, etc... specialist TV distribution equipment suppliers, including Lacey's TV www.laceys.tv

Manmy bthanks Col appreciate the help, will look thru laceyts web site the name does ring a bell ..cheers again

[beeblebrox]

Manmy bthanks Col appreciate the help, will look thru laceyts web site the name does ring a bell ..cheers again

Kingray used to have notched filters can't remember seeing them for a while and hills also sold a version but the usual electrical wholesalers wouldn't have a hope in knowing what you're talking about.

I tend to agree with the above comments on amps, my preference is to use as little as possible but it is often necessary. I would highly recommend the MDA20 kingray series , as they are very good, with low noise figures and engineered for digital.

Ikusi and laceys/fracarro also have amps that also meet that in certain situations.

Even most better larger distribution amps can be remotely powered nowadays so it's then a matter of ensuring they are enclosed in some weather proof enclosure (ideally not in the roof space).

[alanh]

If you reduce the amplified frequency range to the bands used in the viewers' area will remove most troublesome signals which are not TV related. In general the received signal strength of signals from a single site are usually very similar so notch filters are not required. This is one of the reasons why the Kingray MDA series except (MDA20) are so good.

Wideband amplifiers which are still very common are all vunerable to overload from unwanted signals including strong FM broadcasts and power line interference.

AlanH