How do old fashioned masthead amps work?

[zikkimalambo]

Managed to get up to my aerials last week and took down a Teleste Masthead Amp (I think they must have become Labgear, as they seemed to have been selling the same 4 way Masthead Distribution Amp in 2005) According to their catalog it gives 12db of gain on all outputs.

Looking inside, it has about 6 coils (inductors?) and about 3 resistors. It needs 12V to power it, thing is, i' m used to multi legged dvices like transistors and valves being needed to apmlify signals. how can you do it with just coils and resistors?

Apart from screening are the modern designs much different?

I need to decide whether to replace it and if so what to replace it with. I am tempted by a variable gain 25db unit, so as I can play around with the settings and hopefully improve DTT reception.

I have what I think is an 18 element contract group A aerial pointing a CP (approx 27 miles distant (i'm in RH13 0SG). This with the masthead amp gave good analogue signals, but there was just a little pixellation with DTT (worse on the COM muxes).

I have replaced all but the top three feet or so of cable with "satellite cable" (aluminium screening rather than copper on copper :=(( (F connectors and self amalgamating tape) and at the moment just have a 6db SLX2B amp splitting the signal for the 2 DTT boxes. Cable currently goes approx 30 foot to TV 1 where the signal is split, then approx 30 foot onto TV2. I do intend to run a second cable from the loft to TV2 so the split can take place there. it would then be approx 10 foot to split/amp and 20 foot to TV1 and 40 foot from the loft split/amp to TV2.

Anyone still with me?

If so, does my proposal to split and amplify in the loft sound good? If so, reuse the Teleste, or move the SLX up there in the hope that amplifiying the signal nearer the source will be good enough? Or go for the 29db sooper dooper variable gain jobby?

[The Natural Philosopher]

You cant/ It must have transitsors in, they might not look like you expect, thats all.

I think variable gain is a waste of money.

All you care about is not overloading the amplifier with a huge aerial signal, and not overloading the TV with a huge boost.

If you have either situation you just use a passive attenuator anyway.

About 12-20dB is nice, if its then split off. It allows you to drive cables at a shade above what a conventional aerial would produce, which is perfect.

[tony sayer]

In article , [e-mail] scribeth thus

There will be an active device in there somewhere, prolly the other side of the board..

There are better ones around..

From the look of it your in a not very good area there!.

Try a post over to uk.tech.digital-tv

There some very knowledgeable people there...

[Andy Hall]

It may also be worth contacting Ofcom. They were pretty helpful a couple of years back when I was implementing a system of two antennas (Hannington and Crystal Palace) plus distribution. I have a somewhat awkward site situation because CP is relatively far away and the land slopes upwards a little in that direction. Hannington should be providing good signals but has a deliberately distorted coverage pattern in order to avoid certain interferences with other channels from other transmitters. Ideally, I would have wanted to pick one of the transmitters for ultimate DTT use but learned that characteristics would be likely to change once analogue signals are removed. In the end, I implemented antennas and filters for both, that can be adjusted later.

Ofcom's site has a selection of technical documents - for example:

may wrap)

I noticed that there are comments that at the OP's location, the two transmitters that might be expected to provide coverage (Midhurst and Heathfield) may do so poorly because of similar bending to that used at Hannington.

Therefore, it may be worth checking to see what the future as well as the present situation is and whether CP is and will remain the best choice.

[Peter Crosland]

Post your question in uk.tech.digital-tv and ask for Bill Wright who will give you chapter and verse. A very knowledgeable and helpful bloke not to mention being a wonderful yarn teller.

Peter Crosland

[e-mail]

[zikkimalambo]

I know him well, and enjoy reading his misives.

[zikkimalambo]

Yup, and the tinyest "magic smoke container" i've ever seen!