How do profesional riggers "point" an aerial.

In message , wrote


The only problem I found was optimising the aerial position across the
different multiplexes and, unless you have several signal strength
meters, I think that problem would be the same with a 'proper' meter.


Didn't you find the screen that shows all signal strengths and signal to
noise figures for all MUXs on the same screen?
--
Alan

"Phil Cook" wrote in message
...

And you may well get a cowboy ;-(
--
And don't you just.....

The "recommended" outfit that fitted my new " digital" aerial dropped the
lead-in over the roof, over the gutter and down the wall - and about the
only place they used a cable clip was straight into the lead flashing that's
supposed to keep the water out of my single storey extension. Doncha just
love 'em?

Chas

On Mon, 25 Oct 2004 21:18:30 +0100, Alan
wrote:

| In message , wrote
|
|
| The only problem I found was optimising the aerial position across the
| different multiplexes and, unless you have several signal strength
| meters, I think that problem would be the same with a 'proper' meter.
|
|
| Didn't you find the screen that shows all signal strengths and signal to
| noise figures for all MUXs on the same screen?

Non of my three STBs have such a screen. :-(

--
Dave F

Alan wrote:
In message , wrote


The only problem I found was optimising the aerial position across the
different multiplexes and, unless you have several signal strength
meters, I think that problem would be the same with a 'proper' meter.


Didn't you find the screen that shows all signal strengths and signal to
noise figures for all MUXs on the same screen?

Maybe I did, I can't quite remember. There isn't a screen that shows
all three paramters for all MUXes is there though?

--
Chris Green

The only problem I found was optimising the aerial position across the
different multiplexes and, unless you have several signal strength
meters, I think that problem would be the same with a 'proper' meter.


That's just one reason why a spectrum analyser can be handy. It can be
fascinating to watch the various channels as they are affected by, say,
reflections from an aeroplane or propagation anomalies.

Having said that, it is really quite unusual to have different optimum
positions for each channel. When that does happen it normally means that even
the 'optimum' positions are actually a long way from being really good
positions. What I mean is, the 'optimum' positions are probably 15 to 20dB
below what they would be if the aerial wasn't badly screened by buildings,
trees, or hills. You need to be maybe 15dB below the line-of-sight figure for
the effects of screening to start giving significantly odd results, like
different maxima for different channels. This often means that reception will
be unreliable or even permanently poor. Maybe you can't do anything about it,
but maybe you can by spending a bit of time or money. If you are getting
different maxima in the loft, you really should try to get the aerial
outside.Otherwise, accept that you're doing a severely compromised job.

Normally, if you align the aerial for the weakest mux the others will be
optimised as well.

Incidentally, the beamwidth of a yagi is usually a bit narrower if anything
towards the top end of the frequencies it covers, and since the higher channels
also tend to suffer more from screening, if all else is equal use a higher
channel to align the aerial.

Sorry this reply is a bit disjointed, but the cat wants me to groom him and is
nudging my hands as I type. I'll disjoint him if he doesn't behave!

Bill

Bill wrote:

Having said that, it is really quite unusual to have different optimum
positions for each channel. When that does happen it normally means that even
the 'optimum' positions are actually a long way from being really good
positions. What I mean is, the 'optimum' positions are probably 15 to 20dB
below what they would be if the aerial wasn't badly screened by buildings,
trees, or hills. You need to be maybe 15dB below the line-of-sight figure for
the effects of screening to start giving significantly odd results, like
different maxima for different channels. This often means that reception will
be unreliable or even permanently poor. Maybe you can't do anything about it,
but maybe you can by spending a bit of time or money. If you are getting
different maxima in the loft, you really should try to get the aerial
outside.Otherwise, accept that you're doing a severely compromised job.

I know it's a compromise but since it works OK now that's good enough.

Putting the aerial outside (as I have explained in posts quite a while
ago) would be a real pig to do.


Normally, if you align the aerial for the weakest mux the others will be
optimised as well.

Incidentally, the beamwidth of a yagi is usually a bit narrower if anything
towards the top end of the frequencies it covers, and since the higher channels
also tend to suffer more from screening, if all else is equal use a higher
channel to align the aerial.

I think I ended up realising this, one of the MUXs here is a lot
higher in frequency than all the others and if that works OK they
usually all do. The only oddity I have is that there appears to be a
reflection or standing wave or some such which affects the BBC1 MUX
and the best position for all the other MUXs drops BBC1 into a trough.
It just need the aerial dropeed a few inches to sort this though and
that didn't have a big effect on the other signals.


Sorry this reply is a bit disjointed, but the cat wants me to groom him and is
nudging my hands as I type. I'll disjoint him if he doesn't behave!

Strangely our cats don't disturb me when I'm typing here, they sit on
my chest in bed and on my lap at breakfast.

--
Chris Green

On Sun, 24 Oct 2004 21:53:56 GMT, harrogate2
wrote:

It is the CURRENT that hurts - 10mA will hurt, 30mA across the heart
will kill.

Question: So how do 30mA trips save you then?
Answer: Time is a relevant factor as well as current. 30mA for 30ms should
trigger the trip.