On 28/10/14 19:04, gareth wrote:
I have stated my view that short antenna are poor radiatiors based
upon a number of physics and electromagnetics text books in
my possession.

Some have chosen to disagree, and repeatedly so, but their
case is weakened because they produce no evidence and seem
to want to rely on aggressive and abusive remarks in order
to win the day. (I have no interest in winning the day, only in
knowing the truth, which for me at the moment is that short
antennae are poor radiators, and I have no need to resort to
abuse to state that viewpoint)

One is reminded of the religions of the world, firstly Christianity
and latterly Islam that rely on violence to put their message across,
but that reliance is surely an indication that their messages are false,
for, if true, the message would stand up for itself.

If you wanted everybody to profess falsehood, such as saying that 1 + 1 = 3,
or that short antennae are as good radiatiors as long antennae, then you
could only hope to get that message across by the propaganda of abuse,
which is regrettably what we are seeing in this NG, by a number of people
who,
although they might now be wearing long trousers, have minds that are
still wearing nappies / diapers.

Maybe I've missed something here, but I would expect a half-wave dipole
to out-perform a full-wave dipole at the same frequency, despite being
half the size.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk
..
Ubuntu 12.04
Thunderbirds are go.

On 29/10/14 16:27, Jeff wrote:

Maybe I've missed something here, but I would expect a half-wave dipole
to out-perform a full-wave dipole at the same frequency, despite being
half the size.

Define what you mean by "out perform"!!!

A 1/2 wave dipole will half a max gain of about 2.14db in free space
broadside to the antenna, a full wave dipole will be a little over 3db.
However, if you examine the pattern of the full wave compared to the 1/2
wave the lobes of the full wave will be narrower. ie although more power
is radiated in a direction normal to the antenna less is radiated in
other directions, or to put is another way all of the power applied to
the antenna structure is radiated in both cases, but the full wave
concentrates to more into the direction normal to the antenna.

Of course this does not take into account any losses associated with
matching the full wave.

Jeff

OK, Jeff, I don't think I worded that too well. I've never bothered to
learn complex mathematical formulae just for the sake of it. I prefer to
try to visualise things as simply as I can make them.
In the case of a half-wave dipole, at the instant the voltage at one end
goes to peak positive the other end will be at peak negative, and
maximum current will flow.
In a full wave dipole the voltage at both ends will always be in phase,
so I would expect to see a very high impedance at the feed point.
As you point out, matching the full-wave could be difficult and very lossy.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk
..
Ubuntu 12.04
Thunderbirds are go.

In message , Frank Turner-Smith G3VKI
writes



In a full wave dipole the voltage at both ends will always be in phase,

Are you sure? Think on't!

so I would expect to see a very high impedance at the feed point.

Correct.

As you point out, matching the full-wave could be difficult and very lossy.

Double zepp?

--
Ian

On 30/10/14 08:47, Ian Jackson wrote:
In message , Frank Turner-Smith G3VKI
writes
In a full wave dipole the voltage at both ends will always be in phase,

Are you sure? Think on't!

so I would expect to see a very high impedance at the feed point.

Correct.

As you point out, matching the full-wave could be difficult and very
lossy.

Double zepp?

OK, what did I miss? In a full wave dipole, at the instant the voltage
at one end is peak positive, the voltage at the other end will also be
peak positive. Similarly, at the feed point, both legs would be at peak
negative and no current would flow in the feeder, hence the high
impedance. There would be a current flowing in each leg of the dipole,
but the currents would be in anti-phase. Where have I got it wrong? Do I
need another drink?

--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk
..
Ubuntu 12.04
Thunderbirds are go.

In message , Frank Turner-Smith G3VKI
writes
On 30/10/14 08:47, Ian Jackson wrote:
In message , Frank Turner-Smith G3VKI
writes
In a full wave dipole the voltage at both ends will always be in phase,

Are you sure? Think on't!

so I would expect to see a very high impedance at the feed point.

Correct.

As you point out, matching the full-wave could be difficult and very
lossy.

Double zepp?

OK, what did I miss? In a full wave dipole, at the instant the voltage
at one end is peak positive, the voltage at the other end will also be
peak positive. Similarly, at the feed point, both legs would be at peak
negative and no current would flow in the feeder, hence the high
impedance. There would be a current flowing in each leg of the dipole,
but the currents would be in anti-phase. Where have I got it wrong? Do
I need another drink?

Maybe I need a drink too. However, all dipoles/doublets have to fed
'push-pull', so when one leg goes +ve, the other leg goes -ve. The
voltage at all points along the antenna that are equidistant from the
feedpoint will be in antiphase, so if the feedpoint is in the centre,
the voltages at the ends will be in antiphase. [Or is my thinking
seriously muddled?]
--
Ian

On 30/10/14 14:04, Ian Jackson wrote:
In message , Frank Turner-Smith G3VKI
writes
On 30/10/14 08:47, Ian Jackson wrote:
In message , Frank Turner-Smith G3VKI
writes
In a full wave dipole the voltage at both ends will always be in phase,

Are you sure? Think on't!

so I would expect to see a very high impedance at the feed point.

Correct.

As you point out, matching the full-wave could be difficult and very
lossy.

Double zepp?

OK, what did I miss? In a full wave dipole, at the instant the voltage
at one end is peak positive, the voltage at the other end will also be
peak positive. Similarly, at the feed point, both legs would be at
peak negative and no current would flow in the feeder, hence the high
impedance. There would be a current flowing in each leg of the dipole,
but the currents would be in anti-phase. Where have I got it wrong? Do
I need another drink?

Maybe I need a drink too. However, all dipoles/doublets have to fed
'push-pull', so when one leg goes +ve, the other leg goes -ve. The
voltage at all points along the antenna that are equidistant from the
feedpoint will be in antiphase, so if the feedpoint is in the centre,
the voltages at the ends will be in antiphase. [Or is my thinking
seriously muddled?]

Looks like I owe you a pint. You've described the situation where a TX
is feeding the dipole. I was trying to visualise the RX conditions, but
it reciprocates. One of us has to be wrong, and I strongly suspect it's
me. Time for a drink.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk
..
Ubuntu 12.04
Thunderbirds are go.

"Frank Turner-Smith G3VKI" wrote in message
...

On 30/10/14 14:04, Ian Jackson wrote:
In message , Frank Turner-Smith G3VKI
writes
On 30/10/14 08:47, Ian Jackson wrote:
In message , Frank Turner-Smith G3VKI
writes
In a full wave dipole the voltage at both ends will always be in phase,

Are you sure? Think on't!

so I would expect to see a very high impedance at the feed point.

Correct.

As you point out, matching the full-wave could be difficult and very
lossy.

Double zepp?

OK, what did I miss? In a full wave dipole, at the instant the voltage
at one end is peak positive, the voltage at the other end will also be
peak positive. Similarly, at the feed point, both legs would be at
peak negative and no current would flow in the feeder, hence the high
impedance. There would be a current flowing in each leg of the dipole,
but the currents would be in anti-phase. Where have I got it wrong? Do
I need another drink?

Maybe I need a drink too. However, all dipoles/doublets have to fed
'push-pull', so when one leg goes +ve, the other leg goes -ve. The
voltage at all points along the antenna that are equidistant from the
feedpoint will be in antiphase, so if the feedpoint is in the centre,
the voltages at the ends will be in antiphase. [Or is my thinking
seriously muddled?]

# Looks like I owe you a pint. You've described the situation where a TX
# is feeding the dipole. I was trying to visualise the RX conditions, but
# it reciprocates. One of us has to be wrong, and I strongly suspect it's
# me. Time for a drink.

With drinking involved, I must throw in my 2 cents.

I'd go with Frank....for full wave assume positive peak at one end, negative
peak in the middle, and positive peak at the other end. (or vice versa)

But, I suppose I should think about it a little more.....Laphroig would help


Wayne
W5GIE/6