Aerial query about dab and fm

Then again, if the phase is out, its going to need a helical aerial
instead!

Brian

It's funny how a "normal mode" helical isn't what I normally think of
as a helical, (it's a rubber duck)

I suppose the problem is similar with CP is similar to what you said about
MP, it's OK if the TX is on the periphery of the service area, but an
omni-directional CP aerial is problematic.

--
Graham.

%Profound_observation%

"Brian Gaff" wrote in message
m...
I should know this, but a bit out of touch.
I understand that most of the signals these days are mixed polarity. if
this is the case, could one get a better signal from a weaker transmitter
by stacking both a vertical and horizontal aerial and feeding them in
phase?

Why bother? The same amont of ironmongery would put the two aerials onto the
same polarisation, which would make it far easier to phase them. I don't
know if any design of mixed polarisation aerial has more gain than a plane
polarised aerial of the same size and weight.

Bill

"Brian Gaff" wrote in message
m...
I should know this, but a bit out of touch.
I understand that most of the signals these days are mixed polarity. if
this is the case, could one get a better signal from a weaker transmitter
by stacking both a vertical and horizontal aerial and feeding them in
phase?

Brian


You don't necessarily have to *stack* both a H-pol and a V-pol aerial.

For simplicity dual polarisation aerials use a common boom with elements in
both the horizontal & vertical planes.

Then you can coaxially phase them together, with a switching box to provide
....

Vertical polarisation, Horizontal polarisation,

and slant polarisation at 45 degrees, 135 degrees, 225 degrees, 315
degrees,

and left-hand and right-hand circular polarisations.

Good luck, David

It would probably have a very odd polar diagram if you had mixed
polarisation aerials phased I'd imagine.
It goes without saying that the perceived gain of two aerials is not double
what it is for one, you do tend to sharpen the beam of course.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Bill Wright" wrote in message
...

"Brian Gaff" wrote in message
m...
I should know this, but a bit out of touch.
I understand that most of the signals these days are mixed polarity. if
this is the case, could one get a better signal from a weaker
transmitter by stacking both a vertical and horizontal aerial and feeding
them in phase?

Why bother? The same amont of ironmongery would put the two aerials onto
the same polarisation, which would make it far easier to phase them. I
don't know if any design of mixed polarisation aerial has more gain than a
plane polarised aerial of the same size and weight.

Bill

Yes, I played with this with an old band one antex aerial back a lot of
years ago. Its actually quite fascinating and time consuming at the same
time!

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"David Butler" wrote in message
...

"Brian Gaff" wrote in message
m...
I should know this, but a bit out of touch.
I understand that most of the signals these days are mixed polarity. if
this is the case, could one get a better signal from a weaker
transmitter by stacking both a vertical and horizontal aerial and feeding
them in phase?

Brian


You don't necessarily have to *stack* both a H-pol and a V-pol aerial.

For simplicity dual polarisation aerials use a common boom with elements
in both the horizontal & vertical planes.

Then you can coaxially phase them together, with a switching box to
provide ...

Vertical polarisation, Horizontal polarisation,

and slant polarisation at 45 degrees, 135 degrees, 225 degrees, 315
degrees,

and left-hand and right-hand circular polarisations.

Good luck, David

In article , Graham.
wrote:


"Jim Lesurf" wrote in message
...
In article , Brian
Gaff wrote:
I should know this, but a bit out of touch. I understand that most of
the signals these days are mixed polarity. if this is the case, could
one get a better signal from a weaker transmitter by stacking both a
vertical and horizontal aerial and feeding them in phase?

In principle, yes. In practice you may find that the phase delay
varies from one station to another, and with the location of the
antenna. 'Mixed' does not guarantee what you get will be 45 deg slant.

Is a 45deg slant what is intended?

Not necessarily, but is what (by implication) you'd be trying to pickup if
you link the H and V 'in phase'. So it is what the RX antenna would be
'intended' to sense.

If so, I must have misunderstood what mixed pol is.

Depends what you mean. The TX may be a defined ellipse. But by the time you
pick it up it could be quite different.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Brian Gaff
wrote:
Then again, if the phase is out, its going to need a helical aerial instead!

That implicitly assumes circular. The problem is that the polarisation that
reaches you antenna location can be almost anything as it can be altered by
the details of the paths to your location. May also vary from one station
to another, even from the same TX.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Brian Gaff
wrote:
Hang on though, if you use a 45 deg slant, the polarisation is only
slant in two directions. So how is the transmitting aerial made? Do we
have a panel of dipoles with alternate vertical and horizontal, all fed
with equal signals, if so then the edge on signal will surely be
vertical.

Depends on the TX antenna arrangement chosen.

For example, consider two dipoles in the H-plane. One aligned E-W the other
N-S. Drive them with a 90 deg phase difference. The result looks like H-pol
in all directions in the horizontal plane.

Now add a vertical dipole. Drive it with any arg choice of relative phase.

The result will be 'mixed' in that either a V or H antenna will pick up
something (ignoring all the propgation problems). But the actual
polarisation state will change around for locations around the horizontal
plane.

You can now put together a variety of combinations of H and V dipoles. Or
use some other base-elements like helix, and get a 'mix' with other
patterns of pol variation as you move around the TX antennas is the
horizontal plane.

All 'mixed' means is 'mixed'. :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Bill Wright
wrote:

"Brian Gaff" wrote in message
m...
I should know this, but a bit out of touch. I understand that most of
the signals these days are mixed polarity. if this is the case, could
one get a better signal from a weaker transmitter by stacking both a
vertical and horizontal aerial and feeding them in phase?

Why bother? The same amont of ironmongery would put the two aerials onto
the same polarisation, which would make it far easier to phase them. I
don't know if any design of mixed polarisation aerial has more gain
than a plane polarised aerial of the same size and weight.

That does depend on how you'd define 'gain' in this context. :-)

The problem is that the antenna may not match the polarisation state of the
fields arriving. By arranging for a match you may get a larger signal level
picked up. This simple because something like a simple plane antenna is
only coupling to part of the field vector.

So in theory you can get more signal. But in practice any gain may be
small, and you have to fiddle about to match the antenna to match the
signal polarisation ellipse. That may also change from one station to
another. So you'd have to be desperate or lucky. Simpler to just go out and
get a bigger array. :-)

Hence this is one of those 'nice in theory' ideas that in practice is
unlikely to be worthwhile for general broadcasting reception.

May be very different for links over defined paths, though. Particularly
where the path is essentially well away from the ground.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html