RadioBanter - j-pole 5/8 wave

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On Oct 5, 11:49 am, K7ITM wrote:
On Oct 5, 6:45 am, wrote:

Higher?? You posted 6.34dBi for the half wave, and 6.58dBi for the
quarter wave GP ... Am I misreading something, or was that a typo
about which has higher gain, or what?

Dang.. I guess I had it backwards in the 2nd post...
Normally, I would think the 1/2 whip would show slightly higher,
but dunno.. Quiver in the force I guess.
I have no real problems with either type. A 1/2 wave whip is fine
if it's decoupled.
But few J pole users seem to add decoupling sections.
Most of the ringos sold for VHF lack decoupling also..
One note.. If I build a 1/2 wave, I usually prefer to feed as a ringo,
vs as a J pole..
But I still mostly use the GP's as they are simple. I've got one up
in the attic hanging from the rafters as an emergency antenna
when T-storms are in the area and I'm chicken to use my outside
antennas.
MK

K7ITM wrote in news:1191602989.414910.321210
@r29g2000hsg.googlegroups.com:

....
results, Mark. And thanks to Roy for pointing out that the GP doesn't
fully isolate the feedline from antenna currents. I should say
"pointing out once again" as I know he's posted it before, now that
I'm reminded about it. I don't have time at the moment, but put it on
the list to play with in simulations when I have some time.

It is an interesting topic for modelling.

I wrote some notes up after modelling an unloaded elevated vertical as a
multi-band HF antenna. I was particularly interested in the effectiveness
of decoupling of the mast / feedline and the loss implications of mast
current flowing to ground. The article is at
http://www.vk1od.net/multibandunload...ical/13mEV.htm . The spikes in
loss in Fig 3 and 4 are mainly due to loss in the simulated resistance of
the earth connection at the lower end of the mast.

So, the issue is not just about pattern distortion, efficiency may be
impacted significantly.

One of the popular antennas amongst our new six hour hams is to use their
StationMaster on 40m and 80m The StationMaster is a half wave vertical
for 27MHz base fed with a parallel tuned circuit and the 50 ohm coax is
tapped onto the coil of the tuned circuit. (A 27MHz version of the once
popular ham ringo... but the coil is multi turn.)

When modelled on a 10m high mast on 40m and 80m, most of the current
moment contribution is from the support mast and the efficiency is low
due to losses in mast current flowing to lossy ground. Additionally,
there a huge transmission line losses. It is a top fed dummy load... but
with the magic of an ATU, it has a VSWR of 1:1!

But, when their investment in ham radio is 6 hours of learning, they
aren't well equipped to appreciate that the StationMaster isn't an
efficient antenna on 40m and 80m.

Owen

On Oct 5, 2:42 pm, Ed Cregger wrote:
wrote:
On Oct 5, 11:49 am, K7ITM wrote:
On Oct 5, 6:45 am, wrote:

Higher?? You posted 6.34dBi for the half wave, and 6.58dBi for the
quarter wave GP ... Am I misreading something, or was that a typo
about which has higher gain, or what?

Dang.. I guess I had it backwards in the 2nd post...
Normally, I would think the 1/2 whip would show slightly higher,
but dunno.. Quiver in the force I guess.
I have no real problems with either type. A 1/2 wave whip is fine
if it's decoupled.
But few J pole users seem to add decoupling sections.
Most of the ringos sold for VHF lack decoupling also..
One note.. If I build a 1/2 wave, I usually prefer to feed as a ringo,
vs as a J pole..
But I still mostly use the GP's as they are simple. I've got one up
in the attic hanging from the rafters as an emergency antenna
when T-storms are in the area and I'm chicken to use my outside
antennas.
MK

Yes, BUT, the 5/8th wave radiator will put more of the signal toward the
horizon, instead of launching it at a 40 degree plus angle away from the
horizon. So while one configuration can have higher dbi ratings, it
doesn't count unless the signal goes where it will be most effective.

Dunno.. You sure you ain't got it backwards? Unless the 5/8 is on a
large
ground plane, etc, it's usually the one with the higher avg launch
angles
vs the 1/2 wave.
The 5/8 with no radials should be pretty bad at that.. Even a set of
1/4 wave radials under a 5/8 will give a fairly poor pattern.
If I were to build a j pole, it would be a 1/2 wave.
If I run a 5/8, I'd have two elements as a collinear, or at least
have 5/8 or 3/4 wave radials. I'd never run just a single 5/8 wave
radiator
on it's own. It's not a "complete" antenna like a 1/2 wave j pole is.
Or to my way of qualifying anyway...
MK

Ed Cregger wrote:

Yes, BUT, the 5/8th wave radiator will put more of the signal toward the
horizon, instead of launching it at a 40 degree plus angle away from the
horizon. So while one configuration can have higher dbi ratings, it
doesn't count unless the signal goes where it will be most effective.

That is born out he

http://www.cebik.com/gp/58.html

I have a friend (engineer) that designs and builds his boats (some
rather large sailboats) with everything quantized mathematically. I
showed up one day with a model sailboat sitting on a carry stand that I
had made. He asked me how I calculated the angles needed to accommodate
the hull accurately. He said that this problem had been bugging him for
a while. I was surprised because this guy is really smart.

I grabbed two rulers and put each one along the side of the boat and
then clamped them at that angle. I then transferred the angle of the two
rulers to a sheet of paper by simply drawing lines along the inside of
the v that was created. His jaw dropped in surprise. He was amazed at
how easy the process was and he realized that the same process would
work with his full size boats. No math required.

While EZNEC is a fantastic program, it is no better than the programmer
that wrote it. No one person can take absolutely every variable into
consideration because many of them are very, very complex and nearly
impossible to quantize.

I suggested a simple 1/2 wave J-pole antenna earlier that was easy to
make, super easy to tune and one that worked very effectively. Yet
everyone is beating their brains out trying to come up with the best
5/8th wave J-pole, even though this design will require lossy matching
devices to get the impedance down to a manageable/acceptable level.
What's up wid dat?

I do realize that figuring out such a design is fun in and of itself and
may be the real purpose of the exercise. Still, I'll betcha no one on
the receiving end of the OP's signal could tell if he was using the
5/8th wavelength J-pole or the 1/2 wavelength J-pole.

W4RNL may have provided the definitive work on the subject.

http://www.cebik.com/vhf/jp4.html

Ed, NM2K

73, ac6xg

wrote:
On Oct 2, 2:06 pm, "Jimmie D" wrote:

The small theroretical gain advantage that a 5/8wl radiator has over a 1/2wl
radiator is dependent on it having a very good counterpoise. However one
may be able to fabricate a 5/8wl antenna with a couterpoise matched to the
feedline with a stub made of metal tubing.

Jimmie
The best "counterpoise" for a 5/8 radiator is a set of 5/8 radials...
But in that case, it's more of a collinear.
Myself, I think a 5/8 radiator should always be used with a 5/8
lower section of you want the full performance. IE: dual 5/8
collinear.
Anything else is a perversion... :/
My 2nd choice would be to use 3/4 wave radials.
1/2 wave radials would be useless.
1/4 wave radials are semi useless, and give a lousy pattern..
MK

I like the 5/8th on VHF because it has noticably more gain than a
1/4wl groundplane and in my opinon is easier to build and match than
an end-fed 1/2wl antenna.

Jimmie

Ed Cregger wrote:

...
I suggested a simple 1/2 wave J-pole antenna earlier that was easy to
make, super easy to tune and one that worked very effectively. Yet
everyone is beating their brains out trying to come up with the best
5/8th wave J-pole, even though this design will require lossy matching
devices to get the impedance down to a manageable/acceptable level.
What's up wid dat?
...
Ed, NM2K

Until recently, I owned an all fiberglass houseboat--beautiful rig.
However, on fresh water it offered no counterpoise properties whatsoever.

A continuously loaded 1/2 wave end fed vertical utilizing a modified
gamma match feed ended up the solution, and one which required a minimal
counterpoise.

Regards,
JS

Ed Cregger wrote:

Yes, BUT, the 5/8th wave radiator will put more of the signal toward the
horizon, instead of launching it at a 40 degree plus angle away from the
horizon. So while one configuration can have higher dbi ratings, it
doesn't count unless the signal goes where it will be most effective.
. . .

When mounted on a perfect ground plane of infinite extent, any ground
mounted vertical monopole higher than 1/2 wavelength will have one or
more high angle lobes. As the height increases above 1/2 wavelength, the
gain at the horizon increases even though a high lobe appears at around
60 degrees above the horizon. The gain at the horizon peaks out at about
5/8 wavelength, where the high lobe is about 9 dB weaker than the main
lobe. As the antenna gets longer than 5/8 wavelength, the power going
into the upper lobe starts reducing the gain at the horizon (and the
lobe's elevation angle slowly drops) until at one wavelength, all the
power goes to the upper lobe and there's no radiation at the horizon at all.

The gain increase of 1/2 or 5/8 wavelength antennas over shorter
monopoles comes about by a narrowing of the lobe pointing toward the
horizon. Unfortunately, though, radiation at the low angles is severely
attenuated by reflection from real ground. And this is just where most
of the power from longer verticals is going. So a 5/8 wave HF vertical
usually won't exhibit the gain over a shorter antenna you see with a
perfect ground simulation. Likewise, a finite ground plane like a car
roof impacts low angle radiation, so it has more of an effect on a 1/2
or 5/8 wave radiator than a shorter one, and once again you often won't
see the gain you might expect.

A few minutes with the demo version of EZNEC or a similar program shows
the effect of finite ground on various antenna heights very clearly. Use
MININEC-type ground to eliminate the separate effect of ground system
resistive loss. The full EZNEC program will let you model an antenna on
a car top (by using a wire grid to simulate the car top).

Roy Lewallen, W7EL

On Sat, 06 Oct 2007 17:22:07 -0700, Roy Lewallen
wrote:

The gain increase of 1/2 or 5/8 wavelength antennas over shorter
monopoles comes about by a narrowing of the lobe pointing toward the
horizon. Unfortunately, though, radiation at the low angles is severely
attenuated by reflection from real ground. And this is just where most
of the power from longer verticals is going. So a 5/8 wave HF vertical
usually won't exhibit the gain over a shorter antenna you see with a
perfect ground simulation. Likewise, a finite ground plane like a car
roof impacts low angle radiation, so it has more of an effect on a 1/2
or 5/8 wave radiator than a shorter one, and once again you often won't
see the gain you might expect.

A few minutes with the demo version of EZNEC or a similar program shows
the effect of finite ground on various antenna heights very clearly. Use
MININEC-type ground to eliminate the separate effect of ground system
resistive loss. The full EZNEC program will let you model an antenna on
a car top (by using a wire grid to simulate the car top).

It more that just the car's roof that impacts the antennas' radiation
patterns. The car's whole body has a significant effect and there will
be variations - sometimes large - between different vehicles.

http://k6mhe.com/files/mobile_vhf_ant.pdf

Danny, K6MHE

On Oct 6, 3:19 pm, "Jimmie D" wrote:

If I remember correctly the oft quoted theorotical gain of a 5/8ths is with
a groundplane that extents to infinity.
5/8ths with sloping 5/8th radials are begining to perform more like a
ceterfed collinear.

Jimmie

Exactly. That is what you want. A 5/8 element is only half an
antenna,
and the other half wants to be a 5/8 too to work properly. All a 5/8
GP
is , is half of an EDZ. You would never want to run only half of an
EDZ,
or use a 1/4 wave leg on one side, etc.. Like I say, it's a
perversion.
The 1/2 wave is the only single element that can be a proper complete
antenna on it's own. Or according to the laws of NM5K anyway... :/
And of course, even that "complete" antenna needs decoupling from
the feedline to live up to it's full potential.
The success of a 5/8 antenna varies a lot across the spectrum.
On 2m, I hate em... Not a good pattern for VHF, unless you use the
collinears, etc..
But... On 10m, it's my favorite vertical.. I've done careful tests
over
the years, and I've never had any other type single element beat it.
But... I was using 3/4 wave radials the last time I did do testing
on all those.
In one test, I started with a 1/4 wave GP with sloping radials.
Worked ok..
Then I built a 1/2 wave whip, and fed as a ringo.
I saw an improvement over the 1/4 GP, even with no decoupling.
So, I then decided to add a decoupling section, using a 1/4 wave
section of the feedline below the feed, and attached to a set of
1/4 radials.
This improved the antenna a good bit. It was really humming
along at that point. I used mainly stable local signals to test
any improvements. When I added the decoupling to the halfwave,
I noticed a bit less bandwidth as far as the antenna, but the
performance was more stable, and I assume would be about the
same no matter what line length I used, etc..
Anyway, I had the half wave working about as well as possible I
think.
Then I built a 5/8 radiator, and used 4 sloping 3/4 wave radials.
Guess what? It beat the decoupled half wave by an easily noticed
margin on the low angle space/ground wave paths I was using to
test. The other stations were spread across town in various
locations, some 30-40 miles away.
If the low angle performance of the 5/8 was crippled, I sure
didn't see it here on 10m. It still had enough gain at low angles
to beat anything else I could try.
BTW, all those antennas were mounted at the same 36 ft height.
I also ran a 5/8 GP on 17m for a while. That antenna beat every
other antenna I had that could be tuned for 17m. IE: wire
dipoles, etc..
I've seen a load of people use the usual "perverted" 5/8 GP
on the CB band. Even with the short 1/4 radials, I never saw
one of those lose to a 1/4 wave GP. On the average CB meter, '
the change from a 1/4 GP to the 5/8 GP was normally good
for about 2 S units on the average CB , if you were talking
across town a ways. I've seen this too many times for it to
be a fluke of nature. This goes back to the early 70's..
Anyway, I like 5/8 verticals on the HF bands. But myself,
I don't use the short 1/4 wave radials.
As far as 5/8 whips on cars, just depends on the path.
Here in Houston, with the flat terrain, a 5/8 will generally
beat a 1/4 wave by a noticable amount, and will usually
have less picket fencing.
But in those cases, the metal under the antenna is fairly
large vs wavelength. IE: a 5/8 at 146 mhz is about 48 inches.
So it doesn't take a huge vehicle to give a decent ground
plane if the antenna is on the roof or trunk.
Myself, I think most mobile 5/8 whips work better than
elevated 5/8 GP's used on the same band.
In some areas, the terrain will favor using the 1/4 wave
though.
Like I say, the usual 5/8 with 1/4 wave straight radials
is generally the pits on 2m, unless some strange quiver
in the force kicks in, like say in phase feedline currents,
etc. And thats fairly rare in the real world. It can happen
though..
A properly decoupled dual 5/8 collinear on 2m is a stout
antenna and will be hard to beat unless you take drastic
measures. Once I get to that point, I switch to a yagi if
I want to do better. A 3 el yagi will pretty much smoke
any practical vertical.
Anyway, the performance of 5/8 antennas varies quite
a bit depending on where you are using them at.
The 5/8 with 3/4 radials I used on 10m was pretty
stout overall. It was the best out of all the usual
lengths.
The real world and the modeling programs don't always
exactly jive..
IE: On Cevics page, he mentions that in his modeling
tests, he seems to think the 5/8 GP was generally
not worth the trouble on the upper HF bands.. IE: 10m
I know from real world use, it is worth it. No doubt
in my mind. But I also know there are much better
radial lengths than the straight 1/4 wave.
BTW, I agree with one thing he mentioned..
Sloping 1/4 radials with the 5/8 is the pits... You want
1/4 wave radials straight out if they are under a 5/8
whip. Sloping them will really whack out the pattern.
But sloping radials are no problem under a 1/4 wave
whip. Now, on the other hand, sloping 3/4 or 5/8
radials under a 5/8 whip are ok.
MK