"David" nospam@nospam wrote in
:


Which antenna is better: 5/8 wavelength vertical or a J pole?

Better for what? For example, a 5/8 whip would usually be better than a J
Pole for mobile applications on a car roof, but that doesn't make it
better for all applications.


Frequency of operation is 145 MHz = 2 metres.

The 5/8 wavelength vertical has a loading coil. There are losses in
the coil.

It is certainly popular to talk down an antenna with loading coils or
traps because they are "lossy".

Everthing in a real world antenna has loss, the issue is the magnitude of
the loss, and the impact of that on system performance for the intended
application.

You might find it hard to believe that some antenna systems incorporate
loss elements in order to reduce feed line loss by more than that in the
introduced elements.

Whilst you have chosen to raise the loss in the coil, you haven't raised
the issue that a J Pole has currents flowing in lossy conductors,
components of which that do not directly contribute to radiation.


The J pole has a quarterwave matching stub. The matching stub provides
an out of phase current which means that there is a cancelling field
close to the radiating element. Also the J pole is end fed, which

This is not a very good way of analysing the J Pole. The U section can be
thought of as carrying currents that have differential and common mode
components. The common mode components contribute directly to radiation
field. You should also consider common mode current on the supporting
structure and feedline.

The 5/8 wave vertical also has potential for significant common mode
current on the supporting structure and feedline, you need to look at the
effectiveness of the decoupling method employed (usually a radial set).

means the transmitter is not connected directly to a maximum current
point.

What does that matter? BTW, neither is the base fed 5/8.

There is a maxim in ham radio that antennas should always be fed at a
current maximum. You could subscribe to that, but you would limit
yourself by excluding a range of good solutions, and with no guarantee
that a current fed antenna is optimum.


Does the J pole have a disadvantage because of the cancelling field

There is not perfect cancellation at all points on the U section.

from the matching stub and the fact that it is end fed?

"End fed", as opposed to a centre fed dipole perhaps. But isn't the 5/8
"end fed"?


Also consider gain and angle of radiation.

The three dimensional gain distribution is important, but dependent on
the common mode issue mentioned above (amongst other things).

It is fair to say that J Poles are very popular, and that they are overly
represented in problems discussed in online fora.

On the other hand, the 5/8 which was once very popular for mobile work in
this area, is long lost, replaced by two, three and four band antennas
where VSWR is more important than any other performance parameters. I use
a 5/8 vertical on my car, and regularly work repeaters mobile at
distances well over 100km. The antenna is more than thirty years old, and
has never required repair despite hitting low trees, carpark roofs etc
lots of times. The modern multiband antennas are not that robust. I
wouldn't even think of a J Pole in this application.

So, "best" can be a quite complex requirement.

Owen

On Nov 7, 4:18*pm, Owen Duffy wrote:
"David" nospam@nospam wrote :



Which antenna is better: 5/8 wavelength vertical or a J pole?

Better for what? For example, a 5/8 whip would usually be better than a J
Pole for mobile applications on a car roof, but that doesn't make it
better for all applications.



Frequency of operation is 145 MHz *= 2 metres.

The 5/8 wavelength vertical has a loading coil. There are losses in
the coil.

It is certainly popular to talk down an antenna with loading coils or
traps because they are "lossy".

Everthing in a real world antenna has loss, the issue is the magnitude of
the loss, and the impact of that on system performance for the intended
application.

You might find it hard to believe that some antenna systems incorporate
loss elements in order to reduce feed line loss by more than that in the
introduced elements.

Whilst you have chosen to raise the loss in the coil, you haven't raised
the issue that a J Pole has currents flowing in lossy conductors,
components of which that do not directly contribute to radiation.



The J pole has a quarterwave matching stub. The matching stub provides
an out of phase current which means that there is a cancelling field
close to the radiating element. Also the J pole is end fed, which

This is not a very good way of analysing the J Pole. The U section can be
thought of as carrying currents that have differential and common mode
components. The common mode components contribute directly to radiation
field. You should also consider common mode current on the supporting
structure and feedline.

The 5/8 wave vertical also has potential for significant common mode
current on the supporting structure and feedline, you need to look at the
effectiveness of the decoupling method employed (usually a radial set).

means the transmitter is not connected directly to a maximum current
point.

What does that matter? BTW, neither is the base fed 5/8.

There is a maxim in ham radio that antennas should always be fed at a
current maximum. You could subscribe to that, but you would limit
yourself by excluding a range of good solutions, and with no guarantee
that a current fed antenna is optimum.



Does the J pole have a disadvantage because of *the cancelling field

There is not perfect cancellation at all points on the U section.

from the matching stub and the fact that it is end fed?

"End fed", as opposed to a centre fed dipole perhaps. But isn't the 5/8
"end fed"?



Also consider gain and angle of radiation.

The three dimensional gain distribution is important, but dependent on
the common mode issue mentioned above (amongst other things).

It is fair to say that J Poles are very popular, and that they are overly
represented in problems discussed in online fora.

On the other hand, the 5/8 which was once very popular for mobile work in
this area, is long lost, replaced by two, three and four band antennas
where VSWR is more important than any other performance parameters. I use
a 5/8 vertical on my car, and regularly work repeaters mobile at
distances well over 100km. The antenna is more than thirty years old, and
has never required repair despite hitting low trees, carpark roofs etc
lots of times. The modern multiband antennas are not that robust. I
wouldn't even think of a J Pole in this application.

So, "best" can be a quite complex requirement.

Owen

Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has
more gain than a 1/4 wl antenna and is easier to match to 50 ohms than
a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna
than a .5 wl version. From information I have seen the 5/8 often
touted for its low angle of radiation may actually have a
significantly higher angle of radiation than the .5 wl antenna used in
a similar situation. This is not to say either antenna would not be
equally useful.

Jimmie

On Nov 10, 3:46*pm, JIMMIE wrote:
On Nov 7, 4:18*pm, Owen Duffy wrote:



"David" nospam@nospam wrote :

Which antenna is better: 5/8 wavelength vertical or a J pole?

Better for what? For example, a 5/8 whip would usually be better than a J
Pole for mobile applications on a car roof, but that doesn't make it
better for all applications.

Frequency of operation is 145 MHz *= 2 metres.

The 5/8 wavelength vertical has a loading coil. There are losses in
the coil.

It is certainly popular to talk down an antenna with loading coils or
traps because they are "lossy".

Everthing in a real world antenna has loss, the issue is the magnitude of
the loss, and the impact of that on system performance for the intended
application.

You might find it hard to believe that some antenna systems incorporate
loss elements in order to reduce feed line loss by more than that in the
introduced elements.

Whilst you have chosen to raise the loss in the coil, you haven't raised
the issue that a J Pole has currents flowing in lossy conductors,
components of which that do not directly contribute to radiation.

The J pole has a quarterwave matching stub. The matching stub provides
an out of phase current which means that there is a cancelling field
close to the radiating element. Also the J pole is end fed, which

This is not a very good way of analysing the J Pole. The U section can be
thought of as carrying currents that have differential and common mode
components. The common mode components contribute directly to radiation
field. You should also consider common mode current on the supporting
structure and feedline.

The 5/8 wave vertical also has potential for significant common mode
current on the supporting structure and feedline, you need to look at the
effectiveness of the decoupling method employed (usually a radial set).

means the transmitter is not connected directly to a maximum current
point.

What does that matter? BTW, neither is the base fed 5/8.

There is a maxim in ham radio that antennas should always be fed at a
current maximum. You could subscribe to that, but you would limit
yourself by excluding a range of good solutions, and with no guarantee
that a current fed antenna is optimum.

Does the J pole have a disadvantage because of *the cancelling field

There is not perfect cancellation at all points on the U section.

from the matching stub and the fact that it is end fed?

"End fed", as opposed to a centre fed dipole perhaps. But isn't the 5/8
"end fed"?

Also consider gain and angle of radiation.

The three dimensional gain distribution is important, but dependent on
the common mode issue mentioned above (amongst other things).

It is fair to say that J Poles are very popular, and that they are overly
represented in problems discussed in online fora.

On the other hand, the 5/8 which was once very popular for mobile work in
this area, is long lost, replaced by two, three and four band antennas
where VSWR is more important than any other performance parameters. I use
a 5/8 vertical on my car, and regularly work repeaters mobile at
distances well over 100km. The antenna is more than thirty years old, and
has never required repair despite hitting low trees, carpark roofs etc
lots of times. The modern multiband antennas are not that robust. I
wouldn't even think of a J Pole in this application.

So, "best" can be a quite complex requirement.

Owen

Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has
more gain than a 1/4 wl antenna and is easier to match to 50 ohms than
a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna
than a .5 wl version. From information I have seen the 5/8 often
touted for its low angle of radiation may actually have a
significantly higher angle of radiation than the .5 wl antenna used in
a similar situation. This is not to say either antenna would not be
equally useful.

Jimmie

It depends on the vehicle and mount location.
I think often a vehicle provides a better lower section
than the usual ground plane with 1/4 WL elements.
I've seen 5/8 whips do quite well on vehicles if they
are mounted in a good location, the best being the
center of the roof. They beat 1/4 WL whips in comparison
tests, and often showed less "picket fencing".
I imagine a 1/2 wave would work well, but I've never
actually tried a 1/2 wave whip on a vehicle due to
it generally being more complex to build and match.
And in the end, I think the 5/8 would probably beat it
anyway.

But in another comparison on 10m, the elevated
5/8 GP's beat the elevated 1/2 wave's I tried.
And all were decoupled from the feed line.
The comparisons were done locally, using the
space/ground wave which is low angle critical,
and the 5/8's always won to stations that were 30-40
miles away vs the 1/2 wave's.

Anyway, I'm not nearly as negative about 5/8 wave
antennas as many people are.
But like I say, I think the 5/8 over 1/4 wave GP scheme
is perverted and can be greatly improved using more
sane designs. :/

The maximum gain for a single element is .64 wave.
And that gain is usually considered appx 3 db better
than a 1/4 wave. But if I remember right, the dual 5/8
collinear is usually rated at about 3 db better than a
vertical 1/2 wave. "appx 5.1 dbi".
For VHF/UHF use, the old AEA Isopoles were one
of the best commercial verticals built as far as gain
and decoupling of the feed line. Those were dual 5/8
designs with lower decoupling cones.
It was the superior decoupling that really made them
shine at low angles.

On Wed, 10 Nov 2010 13:46:12 -0800 (PST), JIMMIE
wrote:

On Nov 7, 4:18*pm, Owen Duffy wrote:
"David" nospam@nospam wrote :



Which antenna is better: 5/8 wavelength vertical or a J pole?

Better for what? For example, a 5/8 whip would usually be better than a J
snip


Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has
more gain than a 1/4 wl antenna and is easier to match to 50 ohms than
a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna
than a .5 wl version. From information I have seen the 5/8 often
touted for its low angle of radiation may actually have a
significantly higher angle of radiation than the .5 wl antenna used in
a similar situation. This is not to say either antenna would not be
equally useful.

Jimmie
In the late 1970's my work car was a tiny Ford Fiesta (AKA "Fiasco"
It was fitted with a 5/8 wave on a fender mount. The transciever was a
Heath 2036 at 5 watts. The antenna did perform very well as far as
distance was concerned.

However, it was tall enough to ping the light fixtures in the many
parking garages that were essential to my job.

The biggest advantage of a J-Pole is that it is not dependent on a
good ground.

John Ferrell W8CCW

On Nov 11, 11:42*am, John Ferrell wrote:
On Wed, 10 Nov 2010 13:46:12 -0800 (PST), JIMMIE

wrote:
On Nov 7, 4:18*pm, Owen Duffy wrote:
"David" nospam@nospam wrote :

Which antenna is better: 5/8 wavelength vertical or a J pole?

Better for what? For example, a 5/8 whip would usually be better than a J

snip



Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has
more gain than a 1/4 wl antenna and is easier to match to 50 ohms than
a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna
than a .5 wl version. From information I have seen the 5/8 often
touted for its low angle of radiation may actually have a
significantly higher angle of radiation than the .5 wl antenna used in
a similar situation. This is not to say either antenna would not be
equally useful.

Jimmie

In the late 1970's my work car was a tiny Ford Fiesta (AKA "Fiasco"
It was fitted with a 5/8 wave on a fender mount. The transciever was a
Heath 2036 at 5 watts. The antenna did perform very well as far as
distance was concerned.

However, it was tall enough to ping the light fixtures in the many
parking garages that were essential to my job.

The biggest advantage of a J-Pole is that it is not dependent on a
good ground.

John Ferrell W8CCW

I ve had both .5 and .64 wl antennas on my big Chevy Van. I cant tell
any significant difference in performance except for a couple of .5
antennas that were really poor performers, I think this may have been
due to matching network design.. Except for this cause I dont see how
there could be any perceptable difference in the two antennas short of
careful measurements on an antenna range..


Jimmie

On Thu, 11 Nov 2010 14:08:39 -0800 (PST), JIMMIE
wrote:


In the late 1970's my work car was a tiny Ford Fiesta (AKA "Fiasco"
It was fitted with a 5/8 wave on a fender mount. The transciever was a
Heath 2036 at 5 watts. The antenna did perform very well as far as
distance was concerned.

However, it was tall enough to ping the light fixtures in the many
parking garages that were essential to my job.

The biggest advantage of a J-Pole is that it is not dependent on a
good ground.

John Ferrell W8CCW

I ve had both .5 and .64 wl antennas on my big Chevy Van. I cant tell
any significant difference in performance except for a couple of .5
antennas that were really poor performers, I think this may have been
due to matching network design.. Except for this cause I dont see how
there could be any perceptable difference in the two antennas short of
careful measurements on an antenna range..


Jimmie

After I could not stand the Fiesta any longer I ordered a new Cadillac
Cimarron. I did not want to drill any holes in the new Caddy so I
bought one of the thru the glass end fed whips. Its performance was OK
and it did not draw attention to the vehicle so I lived with it.
130,000 miles later it went to our son radio, antenna and all! It only
made sense when he was licensed. If I were doing it again I would have
drilled the appropriated hole in the roof above the dome light and
installed a Larsen 2m & 400 antenna. That was the last time I
hesitated about drilling a hole where I needed it.

Now that I am in a 2008 Chrysler Minivan I have taken the lazy way out
and placed a mag mount quarter wave on the luggage rack (no scratching
there) with the coax ty-wrapped to the rack so there is not enough
slack to allow real damage if it gets knocked off. An itty-bitty Yaesu
FT-90 sits on a sticky pad on the dash and plugs into one of the
vehicles many12v power outlets. The power outlets are not like the
cigarette lighters of the past. They are well installed and fused at
20 amps. As long as you purchase a plug to handle the power and trim
the cable to what is necessary all is well.

The FT-90 gets too hot to handle and shuts down on lengthy rag chews
at full power, but does fine at lower power settings.

You can waste a lot of time and money over killing a mobile antenna
for repeater operation. If you are out in the wide open spaces, maybe
it is worth it!
John Ferrell W8CCW