Sutton and Lichfield

On Apr 28, 3:39*pm, Ian Jackson
wrote:
I can see that, if the aerials were side-by-side, splayed, and separated
by a foot or so, each would dipole be somewhat further away from one
transmitter or the other. There would be bound to be some phase
cancellation, leading to the production of nulls.

But I don't think that deep nulls will suddenly appear in the main lobe
as splay is progressively increased from zero. Instead, there will come
a point when the ever-broadening main lobe starts to develop a hole in
the middle.
In fact, the positions of the nulls and the shape of the main lobe of
each aerial are not related related in that way.
Consider a pair of 18 element yagi receiving aerials, side by side,
exactly equidistant from the TX. They are as close together as they
can be consistent with not encroaching in each other's reception
aperture. They are combined using equal feeder lengths and a combiner
that has equal loss on both legs. With the aerials both aligned on the
tx the forward lobe will be much the same as for a single aerial, but
the gain should be slightly better. The nulls caused by the phasing of
the two aerials will be outside the forward lobe. Now suppose the two
aerials are, say, 15 wavelengths apart. The first nulls will now be
within the common forward lobe. Since nulls caused by phase
cancellation are theoretically infinitely deep, even in reality they
will be very deep; far deeper than the opposing effects of the
aerials' forward gain will be able to conteract significantly.

The same thing applies if the aerials are pointing in different
directions. Yes, as long as the forward lobes overlap there will be
some broadening, but the positions of the nulls are fixed by the inter-
aerial spacing and the wavelength, and if they co-incide with the
broadened forward lobe they will just dig a big hole in it. With
unfortunate inter-aerial spacing you could well have a null in the
direction of one transmitter.

Presumably you mean that the Scottish self-help aerials
developed nulls close into the edges of the main lobe which, in the case
of the aerial required for SC and Lichfield, might be in the direction
of the two transmitters.
No, they had used two horizontally polarized logs (chosen for their
broad forward lobe) mounted around a metre apart, side by side, (as I
recall) and aligned about 25deg apart. Each aerial had its own main
amplifier and to be honest I don't think anyone had worried about
cable length or anything.

I have also seen one that used a pair of four bay vertically polarized
BB Grids, mounted side by side. So there were 8 radiating dipoles with
no particular phase relationship. Results were, apparently, 'patchy'.

And also one that had two TC18Bs pointing about 120deg apart, and
there seemed to be no problems at all with that.

Bill

On Apr 28, 7:46*pm, phil wrote:
On 28/04/2010 16:35, Ivan wrote:





" wrote in message
....
On Apr 28, 2:11 pm, Ian Jackson
wrote:
I'm sort-of guessing, but I would have thought that you could obtain a
wide beamwidth by adding the polar diagrams of two medium-gain,
identical aerials. These would be co-located, but mounted with the
required angle of 35 degrees between them (each pointing at its required
transmitter).

They would have to have the dipoles in the same vertical axis. One
dipole would have to be exactly above the other, and they would have
to be fairly close together.

This is how some tx aerials achieve the desired polar response.

In Scotland somewhere there used to be a self helf where they'd tried
this technique but had put the aerials side by side. The result was a
series of nulls across the field, each null being 'infinitely' deep.
Basically, as you went down the street every so often there was a
house with zero reception.

It's interesting the way the aerials are configured on this local relay,
I don't pretend to know anything about the transmission side of things,
so why are they passing through one another?
Also the lower two log periodics, which I presume almost certainly to
be, receiving aerials, pointing towards Mendip, appear to be in closer
proximity to one another than I've seen you recommend (because of
interaction) is there a reason why the same rule doesn't apply as for a
domestic installation?
http://tx.mb21.co.uk/gallery/backwell.php

Standard crossed log configuration for relays, with angles of 90, 120
and 150 degrees being the most usual. *IIRC, 120 gives a nearly cardioid
pattern. *The crossing point is where the log is 'active' in the middle
of the channels used. *Backwell is standard Group B, so the crossing is
where channel 25 (approx) is active.

That'll be 45?

Bill

" wrote in message
...
On Apr 28, 7:46 pm, phil wrote:
On 28/04/2010 16:35, Ivan wrote:





" wrote in message
...
On Apr 28, 2:11 pm, Ian Jackson
wrote:
I'm sort-of guessing, but I would have thought that you could obtain
a
wide beamwidth by adding the polar diagrams of two medium-gain,
identical aerials. These would be co-located, but mounted with the
required angle of 35 degrees between them (each pointing at its
required
transmitter).

They would have to have the dipoles in the same vertical axis. One
dipole would have to be exactly above the other, and they would have
to be fairly close together.

This is how some tx aerials achieve the desired polar response.

In Scotland somewhere there used to be a self helf where they'd tried
this technique but had put the aerials side by side. The result was a
series of nulls across the field, each null being 'infinitely' deep.
Basically, as you went down the street every so often there was a
house with zero reception.

It's interesting the way the aerials are configured on this local
relay,
I don't pretend to know anything about the transmission side of things,
so why are they passing through one another?
Also the lower two log periodics, which I presume almost certainly to
be, receiving aerials, pointing towards Mendip, appear to be in closer
proximity to one another than I've seen you recommend (because of
interaction) is there a reason why the same rule doesn't apply as for a
domestic installation?
http://tx.mb21.co.uk/gallery/backwell.php

Standard crossed log configuration for relays, with angles of 90, 120
and 150 degrees being the most usual. IIRC, 120 gives a nearly cardioid
pattern. The crossing point is where the log is 'active' in the middle
of the channels used. Backwell is standard Group B, so the crossing is
where channel 25 (approx) is active.

That'll be 45?



Backwell is a group 'A' transmitter so maybe a typo?

On 28/04/2010 21:04, Ivan wrote:


" wrote in message
...
On Apr 28, 7:46 pm, phil wrote:
On 28/04/2010 16:35, Ivan wrote:





" wrote in message
...

On Apr 28, 2:11 pm, Ian Jackson
wrote:
I'm sort-of guessing, but I would have thought that you could
obtain a
wide beamwidth by adding the polar diagrams of two medium-gain,
identical aerials. These would be co-located, but mounted with the
required angle of 35 degrees between them (each pointing at its
required
transmitter).

They would have to have the dipoles in the same vertical axis. One
dipole would have to be exactly above the other, and they would have
to be fairly close together.

This is how some tx aerials achieve the desired polar response.

In Scotland somewhere there used to be a self helf where they'd tried
this technique but had put the aerials side by side. The result was a
series of nulls across the field, each null being 'infinitely' deep.
Basically, as you went down the street every so often there was a
house with zero reception.

It's interesting the way the aerials are configured on this local
relay,
I don't pretend to know anything about the transmission side of
things,
so why are they passing through one another?
Also the lower two log periodics, which I presume almost certainly to
be, receiving aerials, pointing towards Mendip, appear to be in closer
proximity to one another than I've seen you recommend (because of
interaction) is there a reason why the same rule doesn't apply as
for a
domestic installation?
http://tx.mb21.co.uk/gallery/backwell.php

Standard crossed log configuration for relays, with angles of 90, 120
and 150 degrees being the most usual. IIRC, 120 gives a nearly cardioid
pattern. The crossing point is where the log is 'active' in the middle
of the channels used. Backwell is standard Group B, so the crossing is
where channel 25 (approx) is active.

That'll be 45?



Backwell is a group 'A' transmitter so maybe a typo?



Sorry, I was in service planning mode, where group A is 21, 24, 27, 31
and group B is 22, 25, 28, 32 etc. Usually, but not always, made relay
planning easier.

Phil

On Wed, 28 Apr 2010 12:20:43 -0700 (PDT), "
wrote:

On Apr 28, 3:39=A0pm, Ian Jackson
wrote:
I can see that, if the aerials were side-by-side, splayed, and separated
by a foot or so, each would dipole be somewhat further away from one
transmitter or the other. There would be bound to be some phase
cancellation, leading to the production of nulls.

But I don't think that deep nulls will suddenly appear in the main lobe
as splay is progressively increased from zero. Instead, there will come
a point when the ever-broadening main lobe starts to develop a hole in
the middle.
In fact, the positions of the nulls and the shape of the main lobe of
each aerial are not related related in that way.
Consider a pair of 18 element yagi receiving aerials, side by side,
exactly equidistant from the TX. They are as close together as they
can be consistent with not encroaching in each other's reception
aperture. They are combined using equal feeder lengths and a combiner
that has equal loss on both legs. With the aerials both aligned on the
tx the forward lobe will be much the same as for a single aerial, but
the gain should be slightly better. The nulls caused by the phasing of
the two aerials will be outside the forward lobe. Now suppose the two
aerials are, say, 15 wavelengths apart. The first nulls will now be
within the common forward lobe. Since nulls caused by phase
cancellation are theoretically infinitely deep, even in reality they
will be very deep; far deeper than the opposing effects of the
aerials' forward gain will be able to conteract significantly.

The same thing applies if the aerials are pointing in different
directions. Yes, as long as the forward lobes overlap there will be
some broadening, but the positions of the nulls are fixed by the inter-
aerial spacing and the wavelength, and if they co-incide with the
broadened forward lobe they will just dig a big hole in it. With
unfortunate inter-aerial spacing you could well have a null in the
direction of one transmitter.

This certainly *sounds* very impressive and scientific to the lay
reader, but I'd like to look at the evidence for myself.
Perhaps Bill or another expert would care to provide some.
Hopefully if an expert does contribute, he will not offer as evidence
one of his own articles.


--- news://freenews.netfront.net/ - complaints: ---

Please note that the previous post was NOT written by me.
If in doubt, just compare the headers.

I think we can all guess which poster would attempt such childish
tricks.

On Friday, April 30th, 2010 17:18:06 +0100, Nemo wrote:

If in doubt, just compare the headers.

How can one know which header lines are valid, and which are forged?

The path line indicates that the posting originated from the
news.netfront.net server which is in Hong Kong.

The NNTP posting host indicates a subscriber to B$kyB broadband services
via Easynet.

The message id indicates the machine is on a host affiliated to
a domain registered by somebody in Saltash, Cornwall.

On Fri, 30 Apr 2010 18:44:57 +0200, J G Miller
wrote:

On Friday, April 30th, 2010 17:18:06 +0100, Nemo wrote:

If in doubt, just compare the headers.

How can one know which header lines are valid, and which are forged?


Who cares? Most of the spurious message's header lines are different
from mine, which is enough to demonstrate that it is not genuine.
No doubt with sufficient effort it could be faked up to look exactly
the same as mine. If he wants to waste that much time he's welcome.
I can't be arsed to discuss it further.

On Apr 30, 5:18*pm, wrote:
Please note that the previous post was NOT written by me.
If in doubt, just compare the headers.

I think we can all guess which poster would attempt such childish
tricks. *

You can tell by the style anyway.

Bill

On Fri, 30 Apr 2010 12:57:21 GMT, lid wrote:

This certainly *sounds* very impressive and scientific to the lay
reader, but I'd like to look at the evidence for myself.
Perhaps Bill or another expert would care to provide some.
Hopefully if an expert does contribute, he will not offer as evidence
one of his own articles.

Bill's story does indeed sound very impressive.
Having done well socially, it is time now for him to develop his
scientific and technical skills.
Bill must learn that to achieve truly universal recognition, he must
also 'put his money where his mouth is', by providing the necessary
evidence and detail to back up his stories.
Simply ignoring or insulting others when challenged is not clever and
does not gain him respect. On the contrary, it makes him appear
shallow and self-centered.