Sutton and Lichfield
 

In message
,
" writes
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.

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. 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.

I suppose that even with one aerial above the other, the two dipoles
might still not quite be co-located, so some cancellation would occur.
But (with luck), the null problem should be less.
--
Ian

Sutton and Lichfield
 

In article
,
wrote:
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

met that from Winter Hill once in parts of Bolton/Horwich.

--
From KT24

Using a RISC OS computer running v5.16

Sutton and Lichfield
 

"Brian Gaff" wrote in message
...
If they are only that far away, you almost need a very wide beam width
Arial. I recall, many moons ago achieving this by actually sawing off an
Antiference Arial so there were only two directors left! Brian

snip top post


If you are going to do that you might as well use just a dipole

A pair of small yagis each pointing at their respective transmitters,
matched with a coax phasing harness would probably be the best solution

Steve Terry
--
Get a free Three 3pay Sim with £2 bonus after £10 top up
http://freeagent.three.co.uk/stand/view/id/5276

Sutton and Lichfield
 

" 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

Sutton and Lichfield
 

On Wed, 28 Apr 2010 09:17:33 +0100, Mark Carver
wrote:

On 27/04/2010 22:52, lid wrote:

I fitted a new aerial and combiner for a mate to receive analogue C5 from
Fawley as his Rowridge aerial was only able to provide ghosty mush from
Rowridge OR Fawley. As I recall they were about 45 degrees apart.

That was a very common problem. Many people within the potential
service area of Fawley couldn't get it with their existing aerials on
Rowridge, and didn't want C5 enough to pay for additional aerials.

I actually lived where both Fawley and Rowridge were to within a gnat's
difference on the same bearing. However, that was no good either,
because BBC 1 on E31 came banging in about 20dB above C5 on E34.
Therefore BBC 1 would 'splash' over C5. I faffed about with filters etc
for ages, and finally obtained satisfactory results, however the next
day C5 popped up crystal clear on Astra 19.2, so I needn't have bothered
! I thought at the time, how handy it would be to have the other four
channels on satellite too ;-)

C5 were desperate to have some coverage on the south coast. Due to the
well-known planning restrictions Fawley was about the only available
site and they went for it.
I doubt if it was ever an economic proposition.

Sutton and Lichfield
 

lid wrote:

C5 were desperate to have some coverage on the south coast. Due to the
well-known planning restrictions Fawley was about the only available
site and they went for it.
I doubt if it was ever an economic proposition.

Indeed not, and in fact the C5 Tx there was closed in March 2009, because
Rowridge needed E34 for DTT in a re-shuffle resulting from Stockland Hill's DSO.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Sutton and Lichfield
 

tony sayer wrote:
In article , Java Jive
scribeth thus
It'll be carrying SC's DVB-T2/HD mux at least until DSO. I suspect
that after DSO it will indeed drop out of use, but I'm sure Mark will
be along in a while to confirm or correct.

Umm.. So whys it carrying that instead of SC.?. Aerial space or cost?..

SC is currently being ripped apart and re-built for DSO next September, with
some transmissions coming from a temporary mast. I'm told it was less of a
faff about to simply transmit this special 7th HD mux from Lichfield, which
has plenty of mast space, and is nice and 'quiet'.

Come DSO in Sept 2011, the HD Mux will of course replace SD Mux B, and along
with the other muxes, transmit from SC at high power.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Sutton and Lichfield
 

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.

The receive antenna are probably spaced to give a narrow VRP, though I
don't know why.

Phil

Sutton and Lichfield
 

On Apr 28, 3:54*pm, charles wrote:

met that from Winter Hill once in parts of Bolton/Horwich.

The solution?

Bill

Sutton and Lichfield
 

On Apr 28, 4:35*pm, "Ivan" wrote:
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?

It's to get the 'active zones' in a vertical line so the outputs of
the two stacks keep in phase with each other. There's a BBC paper
about it somewhere.

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?
I don't think they're all that close, looking at it.

I've played around with logs and I'd say you can put them half a
wavelength at the lowest frequency apart (HP one above the other; VP
side by side) before anything seriously wierd happens. I regularly
stack them one wavelength apart.

Bill