In article ,
The Natural Philosopher wrote:
However what is under discussion is nothing more or less than a length
of 75ohm coax, which it is claimed 'will pick up signals in the sheath'

well so it will, but thats why its earthed and a coax.

It's not earthed when connected to the average TV set.

--
*Bills travel through the mail at twice the speed of cheques *

Dave Plowman London SW
To e-mail, change noise into sound.

In article , The Natural
Philosopher scribeth thus
tony sayer wrote:
In article , The Natural
Philosopher scribeth thus
tony sayer wrote:
In article , The Natural
Philosopher scribeth thus
tony sayer wrote:
In article , The Natural
Philosopher scribeth thus
Andy Wade wrote:

We've done this one
often enough Tony, both here and on uk.tech.digital-tv. If you connect
a coax feeder to a symmetrical aerial (such as the centre-fed dipole of
a typical TV aerial) without using any form of balun then the outer of
the feeder becomes part of the aerial. If you're transmitting, the
outer of the coax will be 'RF-hot' and will radiate, quite possibly
causing EMC problems to low-level parts of the transmitting equipment as
well as safety concerns if high RF power is involved. When receiving,
unwanted signals picked up on this hot feeder will find their way into
the receiver, however perfect the screening of the coax itself.
I don't think that is actually correct.
It is as equally valid to say that the coax outer 'grounds' one limb of
the dipole at its feed end, and it becomes a 'reflector' boosting the
signal into the other half. Ie. the 'balanced' nature of the antenna is
a myth. It doesn't care what the potential is of any limb: what it cares
about is the difference. It can be 'earthed' at any pint.

Baluns are generally valid on unscreened unearthed transmission lines.
Like twisted pair.
I think that Andy's explanation, and these not a lot you can tell 'im
about TV aerials and associated equipment's, is quite adequate for the
layman...

In Transmission you just don't in practice have unbalanced aerials made,
just -not the done thing-;!.....
No, thats not the point.
It is the point as subsequent posts will show. The only inaccuracy in
that statement is where you are driving a Marconi quarter wave vertical
where it is an unbalanced system!...
I am not talking driving anything.

I am talking about receive only.


You just don't get the fact the whether transmitting or receiving the
theory and operation are identical!...


Not so.

It's like saying that wiring up a motor is no different from wiring up a
microphone.

And what is so very different apart from the voltages and currents?..


And in fact its perfectly sensible to run a microphone earth down the
same line as that returning current from a large electric motors.

Of course it is..




--
Tony Sayer

Whether transmitting or receiving the aerial is part of a system and
the theory and operation are identical. If they were not identical
it is difficult to see how a signal could be transmitted between the
two.

Of course television transmitting aerials don't generally look like
television receiving aerials. There are several good reasons for
this, which can be simplified to the fact that the transmissions are
generally in many directions while the reception is (generally) in
one direction.

An exception to this are some of the smaller relays. For example
Aberbeeg http://tx.mb21.co.uk/gallery/aberbeeg.php receives
signals on a log periodic aerial and transmits them on log periodic
aerials.


Good site that Logs are used more because they present easy logistics
in that they can be used for any part of the band. They as you state are
used for receiving and transmitting where oddly enough they behave the
same;!..

Of course their only low power devices and have their own interesting
patterns especially when stacked in various ways.

For high power systems array's of Panels are used, needless to say don't
want any misplaced currents floating around in the Third pic from
Bottom...



http://tx.mb21.co.uk/gallery/stockla...dso/shdso5.php



--
Tony Sayer

In article , Ian White
scribeth thus
tony sayer wrote:
In article , The Natural
Philosopher scribeth thus

I am talking about receive only.


You just don't get the fact the whether transmitting or receiving the
theory and operation are identical!...

Well not identical, but "reciprocal":

Same difference;-)...

whatever affects the transmit
situation will affect receiving in a similar manner.

There can be a communication problem here because RF engineers tend to
take this "reciprocity principle" for granted. Even when thinking about
receiving aerials, they often switch to talking about the transmitting
situation because it is easier to describe. That is perfectly valid
between professionals, but it can leave sceptical outsiders such as TNP
believing they aren't keeping to the subject; when actually they are.

Yep those who know the mysterious black arts of RF know.. Dontcha
know..



--
Tony Sayer

NOTHING TO DO WITH A RECEIVING ANTENNA.

With all due respect there is no difference in an aerial system you use
to transmit and to receive there is nothing that sets them apart in
theory at all.

As I said, a little knowledge is a dangerous thing.

I guess you are the sort of person who runs a 20hp electric motor off
bell wire..cos a piece of wire is a piece of wire, irrespective of the
current its carrying..



N.P. ...

Stop digging;!.....
--
Tony Sayer

On Tue, 07 Oct 2008 10:41:12 +0100, The Natural Philosopher
wrote:

Graham. wrote:
"The Natural Philosopher" wrote in message

Anyway, I have probably only ever seen half a dozen episodes of
Start-Wreck, by accident, through the years.

My Freeview has several channels that pop and jump; the majority being
fine. I'm tempted to try Maplin's signal amplifier. Anyone have
experience on this?

Nicholas Finlay wrote:
On Tue, 07 Oct 2008 10:41:12 +0100, The Natural Philosopher
wrote:

Graham. wrote:
"The Natural Philosopher" wrote in message

Anyway, I have probably only ever seen half a dozen episodes of
Start-Wreck, by accident, through the years.

My Freeview has several channels that pop and jump; the majority being
fine. I'm tempted to try Maplin's signal amplifier. Anyone have
experience on this?

Probably not.

On my system the popping and jumping is nt lack of signal, its lack of
signal quality.

Usually due to interference from other TV transmitters, but multipath
and trees is the in laws problem

In article , The Natural
Philosopher scribeth thus
Nicholas Finlay wrote:
On Tue, 07 Oct 2008 10:41:12 +0100, The Natural Philosopher
wrote:

Graham. wrote:
"The Natural Philosopher" wrote in message

Anyway, I have probably only ever seen half a dozen episodes of
Start-Wreck, by accident, through the years.

My Freeview has several channels that pop and jump; the majority being
fine. I'm tempted to try Maplin's signal amplifier. Anyone have
experience on this?

Probably not.

On my system the popping and jumping is nt lack of signal, its lack of
signal quality.

Usually due to interference from other TV transmitters, but multipath
and trees is the in laws problem


That more often than not can be cured with a satellite dish and Freesat
if they can stomach the idea of a dish that is..
--
Tony Sayer

"tony sayer" wrote in message
...
In article , The Natural
Philosopher scribeth thus
Nicholas Finlay wrote:
On Tue, 07 Oct 2008 10:41:12 +0100, The Natural Philosopher
wrote:

Graham. wrote:
"The Natural Philosopher" wrote in message

Anyway, I have probably only ever seen half a dozen episodes of
Start-Wreck, by accident, through the years.

My Freeview has several channels that pop and jump; the majority being
fine. I'm tempted to try Maplin's signal amplifier. Anyone have
experience on this?

Probably not.

On my system the popping and jumping is nt lack of signal, its lack of
signal quality.

Usually due to interference from other TV transmitters, but multipath
and trees is the in laws problem


That more often than not can be cured with a satellite dish and Freesat
if they can stomach the idea of a dish that is..
--
Tony Sayer




I found that a good aerial and a new downlead fixed my problems.

I have noticed that some people seem to 'knock' Freeview. I think it is
excellent and is good value for money (£20 for box). I am in a poor
reception area and went to Cable to get a good picture about 12 years ago.
About 2 years ago I borrowed a set-top-box and found I could get some
stations so decided to splash out on a new aerial and it works fine - I also
have a distribution amplifier to get it into other rooms. £150 the lot.

"tony sayer" wrote in message
...
In article , The Natural
Philosopher scribeth thus
Nicholas Finlay wrote:
On Tue, 07 Oct 2008 10:41:12 +0100, The Natural Philosopher
wrote:

Graham. wrote:
"The Natural Philosopher" wrote in message

Anyway, I have probably only ever seen half a dozen episodes of
Start-Wreck, by accident, through the years.

My Freeview has several channels that pop and jump; the majority being
fine. I'm tempted to try Maplin's signal amplifier. Anyone have
experience on this?

Probably not.

On my system the popping and jumping is nt lack of signal, its lack of
signal quality.

Usually due to interference from other TV transmitters, but multipath
and trees is the in laws problem


That more often than not can be cured with a satellite dish and Freesat
if they can stomach the idea of a dish that is..

I think you can get sky freesat for £75 ATM or at least I think that's what
currys were selling.

In article ,
tony sayer wrote:
Usually due to interference from other TV transmitters, but multipath
and trees is the in laws problem


That more often than not can be cured with a satellite dish and Freesat
if they can stomach the idea of a dish that is..

Trees can be a problem for satellite reception. As can heavy rain and snow.

--
*Don't worry; it only seems kinky the first time.*

Dave Plowman London SW
To e-mail, change noise into sound.

Nicholas Finlay wrote:

On Tue, 07 Oct 2008 10:41:12 +0100, The Natural Philosopher
wrote:


Graham. wrote:

"The Natural Philosopher" wrote in message


Anyway, I have probably only ever seen half a dozen episodes of
Start-Wreck, by accident, through the years.


My Freeview has several channels that pop and jump; the majority being
fine. I'm tempted to try Maplin's signal amplifier. Anyone have
experience on this?

Because we are in a poor position due to some trees that have grown very
tall, we had a new super duper aerial fitted and that improved things on
both terrestrial and free view, until it rained and the leaves got wet,
then the free view started to pixalate. I bought the same amplifier that
you mention and it has been fine this year, though it didn't do too well
last year in the wet, some of the stations pixalated.

On your free view box, you should be able to find a menu that lets you
see the signal quality and strength on screen. I'll go and see how I get
into it.

Current one has no option, but the Sagem I had before it allowed sig.
strength and quality to be viewed.

Dave