I think I need channel filters


Finally got round to starting to sort out the aerial and distribution system in our new place. To recap: there were two aerials - one high gain group A on crystal palace, and a contract group B on sudbury. These were combined (goruped combiner it turns out) onto a single downlead and fed into a labgear 6 way amp / splitter thence sockets around the house.

I decided to abandon the CP aerial altogether (since the digital muxes were almost down in the noise) and concentrate on Sudbury. Looking at the post switchover allocations suggested a group E aerial. However not being able to find a decent one of those, I took Bill Wright's advice and modified a group B to extend the top end.

Anyway that is now fitted and working nicely (took the opportunity to replace the mortar flaunching on the chimney pots at the same time as these were wobbling!).

I fitted a variable gain masthead amp:

http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/461209.xml

Looking at the feed to the distribution amp (with the gain on the masthead set to minimum) we now get:

Channel Signal Mux
(dBuV)
39 52 D4
48 51 D3
49 52 D1
50 50 D6
54 48 D5
56 48 D2

Which seems like a reasonable starting point, with the Terry meter reporting a "pass" for signal to noise on all the muxes. A problem however is the in band the analogue signals:

44 73 BBC2
51 74 BBC1
(similar level for the others)

Which are at least 20 dB stronger than the digital muxes. (if you ramp up the gain on the masthead I can push these to over 99 dBuV - which is where my meter gives up!)

Trying this through the existing splitter amp still did not give adequate performance. I have come to the conclusion that the labgear is crap anyway (poor noise etc) and the house co-ax wiring leaves much to be desired. Tweaking the gain up on the masthead did not really help much either since I expect it was overloading the input on the splitter amp with the high analogue signals.

Ditching the current splitter amp altogether, and running the masthead on full gain, into a passive splitter got reasonable performance on one socket but marginal on others. Adding a lowish gain setback amp before the passive splitter got good performance on at least two sockets and reasonable on others.

So to get robust and reliable digital on all sockets I could do with a little more headroom coming out of the splitter.

Rewiring the house with decent CT100 will happen at some time - but not in a hurry (the loss one some runs is quite startling - not helped by the previous installer deciding to daisy chain two sockets on some of the runs).


Questions
=========

So should I:

Go with a better distribution amp with moderate gain on each output? If so any recommendations for one that is not going to be upset by the disparity in input levels?

Or

Try to level (or for that mater just notch filter) the analogue signals? (I don't care if we lose all analogue reception)

If the latter, what would be an appropriate device, and when can I order one from?

How easy are these to setup?

--
Cheers,

John.

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