Non powered mast head amplifiers.

La Poste · Mar 6, 2012

How do they work?

I mean I have seen amplifiers that are supposed to be connected to mast heads but they have no power supply.

I always thought that to amplify something you would need a separate power supply so that the smaller signal could be boosted to a larger signal by making use of this external power.

If an aerial signal amplifier has no power supply then how does it boost the signal from the aerial.

Does anyone know?

Thanks.

Richard Burns · Mar 7, 2012

Are these the ones powered from a remote power supply that is fed back to the amp via the coax?

La Poste · Mar 7, 2012

I'm not really sure we have a long length of Co-ax cable at work running from a roof top aerial to the TV at the other side of the building.

I was told we have an inline amplifier in this cable but when I looked at it it had no power supply.

It is just a box where the cable goes in one end and out the other.

I am wondering if it is some sort of signal cleaner you know it filters out the bad stuff and leaves the good and then the signal is amplified at the TV end of the cable.

I shall take some pictures at work tomorrow because I really don't know what it is.

Apparently the guy who installed it was using an oscilloscope.

I have just done some reading on mast head amplifiers and they all seem to need a power supply usually 12 Volts.

Richard Burns · Mar 7, 2012

I cannot see how an amplifier could operate without a larger supply to amplify the signal, are you sure that there is not a power supply box by the TV that feeds the amplifier, I cannot really see the point of a filter box unless there is a lot of signal interference from outside

mhar · Mar 8, 2012

A lot of modern tvs and set top boxes have a menu option for antenna power.
The oscilloscope you refer to could well have been a spectrum analyser. I use one all the time.
The box could well be a filter. Digital tv tuners tune as they find signals, in the main. Our main transmitter is high frequency (group cd), therefore all it's relays are going to be lower frequency (historic due to co channel and +-5analogue interference). Therefore if you are trying to tune to the main transmitter you could well be picking up from a relay as well which your tv will come accross first and tune to. This could be problematic if these signals are noisy as they could well pixelate. By fitting a pass filter for the frequencies you require you eliminate this problem. Best way to see if this affects you is to use a spectrum analyser which shows you everything the aerial is seeing.

La Poste · Mar 8, 2012

Fascinating stuff, thanks for posting.

I just thought I would add this, it's slightly off topic but follows the main vein.
This is from a well know stockist.

The specs are:

"In line amplifier
Ideal for extending HDMI cable runs up to 20M, without loss of signal nor strength.
Powered from Digital Satellite Receiver (RF2)
Supports 480p, 720p, 1080i and 1080p video formats.."

And here's a picture of another.

I wonder how effective they are at amplifying the signal.

Does anyone have any experience of these sorts of gadgets?

mhar · Mar 9, 2012

Pic 1 does exactly what it says. It is for distributing the hdmi signals produced by the satellite receiver - internal distribution around the property.
Pic 2 is for massive cable runs from the dish to the receiver. It is placed at least 2/3rds of the way along the cable (dish end so that you are amplifying a clean signal before it has had much of a chance to degrade in the cable). I have only ever used one once many years ago on a 80-100m run from a dish. My ideal solution to this would have been to use upgraded cable (instead of ct100 use 125 or 167) but it was already in place. However the output from modern LNB's is a lot higher than it used to be (I now have to use 26dB of inline attenuators to reduce the level reaching my spectrum so that it can cope!! whereas I never used to have to use any) so these are a lot less common than they used to be. They amplify the satellite if (intermediate frequency - what the LNB knocks down the very high received frequencies to) so are only used in situations which most people on here are very unlikely to encounter (1 dish feeding a housing estate) but, personally, I would not use one preferring to calculate my losses and use a launch amp at the head end. These inline amps are usually tilt compensated so that they amplify the highest frequencies more than the lower ones in order to cope with cable attenuation which is directly related to frequency.