Andy Wade wrote:
wrote in message
Yes, so how does that affect my suggestion/comment that 'seeing is
believing'? All I was saying was that for someone who is installing
FreeView (and maybe an aerial) themselves observation of the picture
is a good enough indicator of whether it's working.

A few day's observation under normal conditions isn't necessarily a good
indicator of whether it will continue to work 'as planned' all year round...

No, and *if* problems appear after six months then one can make some
small improvements. As I keep saying it's a non-event to have to do
this if it's a DIY installation and I have also said that a commercial
installer *can't* do it.


If it becomes marginal occasionally due to atmospheric/tropospheric
conditions then one either accepts that it is 'as designed' or one
tries some improvements.

... OK, but how do you know that you're not suffering more loss of service
than necessary? Most people won't have a clue what's happening when the
screen goes blank; at least with analogue you see what's happening and most
can recognise "interference" in a general sort of way.

If the screen 'goes blank' then (from my point of view anyway) that's
worse than acceptable. In reality 'interference' on a digital signal
tends to produce artefacts which are recognised by the viewer as
deterioration in the signal.


Using well screened coax is necessary, but not sufficient. Any gaps
in the screening will allow the interference to get in, and poorly
screened outlet plates and flyleads are the other betes noir. At
the other end of the coax, the lack of a balun on the aerial will
also provide a coupling mechnanism.

I've never seen a balanced feeder aerial input on any domestic TV
(or set top box) here in the UK, are you saying that the internal
bodge (which is probably what it is) can pick up impulse
interference?

Uh? Where did I mention needing a balanced i/p on the receiver? Some
pre-war Band-I 405-line TVs had balanced-twin inputs, OOI, but coax has been
univseral since the late 40's (except for VHF TV in the US).

You said "... end of the coax, the lack of a balun on the aerial ...",
are you then saying that there should be a balun at the aerial end of
the coax? I thought that most aerials have a natural impedance of
around 75 ohms which is why 75 ohm co-ax is used. Are you just saying
that there should be a 75 ohm to 75 ohm (as opposed to imedance
matching) balun at the aerial because the aerial is balanced and the
coax isn't? Will this actually provide much improvement? If so it's
a fairly simple and cheap thing to do.


This is true enough but it's not the sort of thing that most people
are willing to do anything about as it would involve
digging around inside the FreeView box. Or are you saying something
else and I've misundestood?

You've misunderstood. The point was that, ideally, you should have a good
balun on the antenna - otherwise RF interference picked up on the outside of
the coax feeder will find its way into the signal path, even if there are no
'leaks' downstream.

Ah, OK, the above *is* what you mean. Can one get ready made 75ohm to
75ohm baluns?

--
Chris Green