In message , Ralph
Mowery writes

"Ian Jackson" wrote in message
...
The original proposal in this thread was that long antennas performed
better than short ones. If that was true you'd get a good 600MHz UHF TV
picture using a 132ft end fed longwire. I've not tried it, but it doesn't
seem very likely.

A 132' endfed will have one hell of a gain on 600MHz - but it will be
almost straight off the ends.
--
Ian
I know the gain will be off the end of the wire, but still wonder if an
antenna that long (in wavelengths) will actually work or will it be too
long and the gain does not meet the expectations or if programs like NEC
will predict it or fall apart.

On that point, you'll have to ask the experts!


--
Ian

On 30/10/14 22:26, Ian Jackson wrote:
In message , Ralph
Mowery writes

"Ian Jackson" wrote in message
...
The original proposal in this thread was that long antennas performed
better than short ones. If that was true you'd get a good 600MHz UHF TV
picture using a 132ft end fed longwire. I've not tried it, but it
doesn't
seem very likely.

A 132' endfed will have one hell of a gain on 600MHz - but it will be
almost straight off the ends.
--
Ian
I know the gain will be off the end of the wire, but still wonder if an
antenna that long (in wavelengths) will actually work or will it be too
long and the gain does not meet the expectations or if programs like NEC
will predict it or fall apart.

On that point, you'll have to ask the experts!


The gain would be at the cost of a very narrow front lobe. You'd need a
big rotator.

--
;-)
..
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 22:26, Ian Jackson wrote:
In message , Ralph
Mowery writes

"Ian Jackson" wrote in message
...
The original proposal in this thread was that long antennas performed
better than short ones. If that was true you'd get a good 600MHz UHF TV
picture using a 132ft end fed longwire. I've not tried it, but it
doesn't
seem very likely.

A 132' endfed will have one hell of a gain on 600MHz - but it will be
almost straight off the ends.
--
Ian
I know the gain will be off the end of the wire, but still wonder if an
antenna that long (in wavelengths) will actually work or will it be too
long and the gain does not meet the expectations or if programs like NEC
will predict it or fall apart.

On that point, you'll have to ask the experts!


The gain would be at the cost of a very narrow front lobe. You'd need a
big rotator.

In the UK, would you be wanting to rotate it for TV? Don't forget that
one type of antenna used in the very early days of BBC TV (Channel 1,
vertical, 45MHz) was a 'sloper. This was an off-centre-fed wire dipole,
with the short leg being a quarterwave, and attached as high as possible
(maybe to a chimney or a gutter). The other leg was an odd number of
quarterwaves, and attached much lower down. As a result, the antenna had
one of its major lobes sort-of off the end (say 30 degrees off the
wire), in a more-or-less horizontal direction, and responding well to
vertically polarized signals.
--
Ian

"Ian Jackson" wrote in message In
the UK, would you be wanting to rotate it for TV? Don't forget that
one type of antenna used in the very early days of BBC TV (Channel 1,
vertical, 45MHz) was a 'sloper. This was an off-centre-fed wire dipole,
with the short leg being a quarterwave, and attached as high as possible
(maybe to a chimney or a gutter). The other leg was an odd number of
quarterwaves, and attached much lower down. As a result, the antenna had
one of its major lobes sort-of off the end (say 30 degrees off the wire),
in a more-or-less horizontal direction, and responding well to vertically
polarized signals.
--
Ian

I have not kept up with TV signals for a long time. In the US they started
off as all horizontal. I think that some may have gone to circular, but not
sure. It might be the FM stations I am thinking about. Not sure what they
are using now on the digital signals.

What are they using in other countries ? Horizontal, vertical ?



---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

In message , Ralph
Mowery writes

"Ian Jackson" wrote in message In
the UK, would you be wanting to rotate it for TV? Don't forget that
one type of antenna used in the very early days of BBC TV (Channel 1,
vertical, 45MHz) was a 'sloper. This was an off-centre-fed wire dipole,
with the short leg being a quarterwave, and attached as high as possible
(maybe to a chimney or a gutter). The other leg was an odd number of
quarterwaves, and attached much lower down. As a result, the antenna had
one of its major lobes sort-of off the end (say 30 degrees off the wire),
in a more-or-less horizontal direction, and responding well to vertically
polarized signals.
--
Ian

I have not kept up with TV signals for a long time. In the US they started
off as all horizontal. I think that some may have gone to circular, but not
sure. It might be the FM stations I am thinking about. Not sure what they
are using now on the digital signals.

What are they using in other countries ? Horizontal, vertical ?

Historically, both. The very first UK TV transmitter (45MHz), launched
in 1936, was vertical. This closed down swiftly on 1 September, 1939,
and WW2 started two days later.

After WW2, TV resumed in 1946. Four more channel frequencies (all BBC
only in those days) were added throughout the country in the Low Band
(Band 1, as we call it), and the split of vertical and horizontal was
around 50/50. In 1954, the independent network (ITV) arrived, all in the
High Band (Band 3) - again with around a 50/50 split.

In 1963 (?) UHF was launched - initially carrying only a second BBC
channel, on 625-lines. Eventually, this expanded to four - and in some
places - five channels, all transmissions being co-sited - or almost
co-sited (so that only one, fixed antenna was required). Without
exception, all high(er) power analogue transmitters were horizontal, and
almost without exception, all the low(er)-power fill-in relay stations
were vertical. Although these days it's all digital, same pertains -
except for (I think) one new fairly high power directional vertical
transmitter.

BTW, the old 405-line VHF network was totally closed down in the 1980s.
Although VHF is no longer used for TV, part of the Band 3 allocation is
now digital radio - all vertical. FM was originally all horizontal, but
gradually the benefits of circular - and the simpler mixed -
polarizations became implemented. Very few are now purely horizontal.

Other European countries have had a somewhat different history, but I'm
pretty sure that very few TV transmitters were/are vertical - except for
local fill-in and low power. For FM, the Irish Republic has always
(sensibly) used vertical.




--
Ian

"Ian Jackson" wrote in message ...

In message , Wayne
writes


"Ian Jackson" wrote in message ...

In message , Wayne
writes


"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

# See:
# http://tinyurl.com/q8nxqep
# ten rows of images down, second from left:

# This shows the amplitude and the polarity of the voltage and current for
# a halfwave dipole. [Lots of diagrams only show the amplitude.] You will
# see that the polarities on each leg are +ve and -ve. For a fullwave,
# just imagine it continuing on for another halfwave each side.

# -- # Ian

Isn't that figure for a full wave?... lambda

# Maybe you're looking at the wrong one. I've had another look, and it's
# now 9 down, far left. It's the one with the thick black dipole, entitled
# "Halfwave Dipole Antenna (Hertz)". Ah, I've found the source, here (Fig
# 1):
# http://www.digikey.com/en/articles/t...standing-anten
# na-specifications-and-operation

# --
# Ian

OK, but I'm losing touch with what the point is.
The figures referenced both times show voltage peaks of opposite phase at
the ends of half wave dipoles, thus voltage peaks of the same phase at the
end of full wave dipoles.

I'm assuming we have agreement on that.

And with that, it currently is time here in CA for Lagavulin 16.

Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
The original proposal in this thread was that long antennas performed
better than short ones. If that was true you'd get a good 600MHz UHF TV
picture using a 132ft end fed longwire. I've not tried it, but it doesn't
seem very likely.

A 132' endfed will have one hell of a gain on 600MHz - but it will be
almost straight off the ends.
--
Ian
I know the gain will be off the end of the wire, but still wonder if an
antenna that long (in wavelengths) will actually work or will it be too
long and the gain does not meet the expectations or if programs like NEC
will predict it or fall apart.

EZNEC handles it just fine.

I modeled a 120' (I had forgotten the exact number posted) long wire
at 6' over real ground at 600 Mhz:

Impedance: 55-j308
Max vertical gain: 21 dBi at 4 degrees
Horizontal gain: two 21 dBi lobes at +/- 4 degrees
Front/back: 9.5 dB

LOTS of little lobes...



--
Jim Pennino

In message , Wayne
writes


"Ian Jackson" wrote in message ...

In message , Wayne
writes


"Ian Jackson" wrote in message ...

In message , Wayne
writes


"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


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

# See:
# http://tinyurl.com/q8nxqep
# ten rows of images down, second from left:

# This shows the amplitude and the polarity of the voltage and current for
# a halfwave dipole. [Lots of diagrams only show the amplitude.] You will
# see that the polarities on each leg are +ve and -ve. For a fullwave,
# just imagine it continuing on for another halfwave each side.

# -- # Ian

Isn't that figure for a full wave?... lambda

# Maybe you're looking at the wrong one. I've had another look, and it's
# now 9 down, far left. It's the one with the thick black dipole, entitled
# "Halfwave Dipole Antenna (Hertz)". Ah, I've found the source, here (Fig
# 1):
# http://www.digikey.com/en/articles/t...standing-anten
# na-specifications-and-operation

# -- # Ian

OK, but I'm losing touch with what the point is.
The figures referenced both times show voltage peaks of opposite phase
at the ends of half wave dipoles, thus voltage peaks of the same phase
at the end of full wave dipoles.

I'm assuming we have agreement on that.

You assume wrongly. A centre-fed fullwave is also fed 'push-pull', ie in
antiphase - except that it's a high voltage feed instead of high
current.

Just draw a diagram similar to the halfwave, - again showing both the
voltage amplitude and polarity. The lines you draw on each side for the
amplitudes are copies of each other - not mirror images.

However, it seems to a different matter if you feed the fullwave
off-centre, a quarterwave from one end. At least on my drawing, the
voltages at the ends ARE in phase - so I guess the radiation pattern
will be different from the centre-fed.

And with that, it currently is time here in CA for Lagavulin 16.

No such luck here. FWIW, it's nearly midday, and I'm having a (rather
late) strong 'coffee-bag' coffee, with two teaspoons of maple syrup and
one teaspoon (heaped) of dark drinking chocolate powder.
--
Ian

On 31/10/14 11:56, Ian Jackson wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , Wayne
writes


"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

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

# See:
# http://tinyurl.com/q8nxqep
# ten rows of images down, second from left:

# This shows the amplitude and the polarity of the voltage and
current for
# a halfwave dipole. [Lots of diagrams only show the amplitude.] You
will
# see that the polarities on each leg are +ve and -ve. For a fullwave,
# just imagine it continuing on for another halfwave each side.

# -- # Ian

Isn't that figure for a full wave?... lambda

# Maybe you're looking at the wrong one. I've had another look, and it's
# now 9 down, far left. It's the one with the thick black dipole,
entitled
# "Halfwave Dipole Antenna (Hertz)". Ah, I've found the source, here (Fig
# 1):
#
http://www.digikey.com/en/articles/t...standing-anten
# na-specifications-and-operation

# -- # Ian

OK, but I'm losing touch with what the point is.
The figures referenced both times show voltage peaks of opposite phase
at the ends of half wave dipoles, thus voltage peaks of the same phase
at the end of full wave dipoles.

I'm assuming we have agreement on that.

You assume wrongly. A centre-fed fullwave is also fed 'push-pull', ie in
antiphase - except that it's a high voltage feed instead of high current.

Just draw a diagram similar to the halfwave, - again showing both the
voltage amplitude and polarity. The lines you draw on each side for the
amplitudes are copies of each other - not mirror images.

However, it seems to a different matter if you feed the fullwave
off-centre, a quarterwave from one end. At least on my drawing, the
voltages at the ends ARE in phase - so I guess the radiation pattern
will be different from the centre-fed.

And with that, it currently is time here in CA for Lagavulin 16.

No such luck here. FWIW, it's nearly midday, and I'm having a (rather
late) strong 'coffee-bag' coffee, with two teaspoons of maple syrup and
one teaspoon (heaped) of dark drinking chocolate powder.

Ian, thanks for your help. There's just one bit of this I can't get my
head around.
I'm happy with the idea of 'push-pull' feeding the antenna. This, as you
say, will cause the amplitudes on each side to be copies and not mirror
images. This in turn causes the currents flowing in the legs to be in
phase, with about 1dB increase in the front lobe and a subsequent
decrease in the lobe's width.
This has to reciprocate, so what happens in RX mode to cause the same
phase inversion at the feed point?

--
;-)
..
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 31/10/14 11:56, Ian Jackson wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , Wayne
writes


"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

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

# See:
# http://tinyurl.com/q8nxqep
# ten rows of images down, second from left:

# This shows the amplitude and the polarity of the voltage and
current for
# a halfwave dipole. [Lots of diagrams only show the amplitude.] You
will
# see that the polarities on each leg are +ve and -ve. For a fullwave,
# just imagine it continuing on for another halfwave each side.

# -- # Ian

Isn't that figure for a full wave?... lambda

# Maybe you're looking at the wrong one. I've had another look, and it's
# now 9 down, far left. It's the one with the thick black dipole,
entitled
# "Halfwave Dipole Antenna (Hertz)". Ah, I've found the source, here (Fig
# 1):
#
http://www.digikey.com/en/articles/t...standing-anten
# na-specifications-and-operation

# -- # Ian

OK, but I'm losing touch with what the point is.
The figures referenced both times show voltage peaks of opposite phase
at the ends of half wave dipoles, thus voltage peaks of the same phase
at the end of full wave dipoles.

I'm assuming we have agreement on that.

You assume wrongly. A centre-fed fullwave is also fed 'push-pull', ie in
antiphase - except that it's a high voltage feed instead of high current.

Just draw a diagram similar to the halfwave, - again showing both the
voltage amplitude and polarity. The lines you draw on each side for the
amplitudes are copies of each other - not mirror images.

However, it seems to a different matter if you feed the fullwave
off-centre, a quarterwave from one end. At least on my drawing, the
voltages at the ends ARE in phase - so I guess the radiation pattern
will be different from the centre-fed.

And with that, it currently is time here in CA for Lagavulin 16.

No such luck here. FWIW, it's nearly midday, and I'm having a (rather
late) strong 'coffee-bag' coffee, with two teaspoons of maple syrup and
one teaspoon (heaped) of dark drinking chocolate powder.

Ian, thanks for your help. There's just one bit of this I can't get my
head around.
I'm happy with the idea of 'push-pull' feeding the antenna. This, as
you say, will cause the amplitudes on each side to be copies and not
mirror images. This in turn causes the currents flowing in the legs to
be in phase, with about 1dB increase in the front lobe and a subsequent
decrease in the lobe's width.
This has to reciprocate, so what happens in RX mode to cause the same
phase inversion at the feed point?

Well..... Errrrrr....... It.... just sort-of does?

As you say, it has to reciprocate, therefore the incoming wavefront(s)
from where the 'radiation' lobes are pointing, induce volts and amps in
the antenna such that they end up being in anti-phase at the feeder
connection points. They then slide, in antiphase, all the way down the
feeder and into the receiver. Or something like that.
--
Ian