El 24-06-13 18:14, Wimpie escribió:
El 24-06-13 14:57, Kickin' Ass and Takin' Names escribió:


It's a long story, here's the short version.

Our volunteer rescue squad dispatch operates in the 152 - 154 MHz
range -- transmit on 154.XXX, receive 152.XXX.

Our main antenna barely survived contact with a tree limb and needs to
be replaced.

Our local Motorola sales rep has his head stuck firmly up his ass and
keeps trying to sell us some basic 1/4-wave verticals.

The current antenna is a vertical whip with a loading coil wound
along the length of the antenna.

The dimensions a

-- Overall height: 14.25 inches
-- 4 inches from the base the antenna is wound into a coil, about 3/8
inch diameter, 5 turns
-- the coil is 1.75 inches long
-- above the coil is 8.5 inches of antenna
-- NMO base

I suspect this antenna is an old model 5/8-wave VHF antenna, shortened
by winding a coil in the antenna.

If it is a 5.8-wave, it should be giving us a few dB gain. The
1/4-wave whip he wants me to install would give unity or less gain. In
our rural area, we need all the antenna help we can get. I an
thinking about installing a full-length 5/8-wave whip, but, we go into
a lot of driveways with low tree limbs and I doubt a full-length
antenna would survive very long.


I have Googled every term I can think of to find this antenna,
Motorola sales rep tells me he thinks its a "cellular antenna" . .
.which it clearly is not. My MFJ antenna analyzer shows a resonance
at 154 MHz.

Anyone help me identify this antenna?


- - - - -

Fat, Dumb, and Ugly
is no way to go through life.

But, if you're a
Republican,
you have no choice.


I agree with others. The full size quarter wave with correct size
radials will perform better then the current 14.25' stick, no matter
how you wind it.

Make sure you have some VSWR indication to tune it to your frequency
range, or just to check the complete installation.


I overlooked the mobile operation from a car. Of course, when the
antenna is mounted on a metal surface, you don't need radials..

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

On Mon, 24 Jun 2013 18:46:46 +0200, Wimpie
wrote:

I overlooked the mobile operation from a car. Of course, when the
antenna is mounted on a metal surface, you don't need radials..

If it's a metal car roof, you don't need radials. Unfortunately, I've
had to deal with verhicles that have a fiberglass roof. Aluminum duct
tape ground plane (on the inside) to the rescue.
http://www.homedepot.com/p/Nashua-Tape-322-1-57-64-in-x-50-yds-Aluminum-Foil-Tape-3220020500/100030120#.Uch4_Ng9pjZ

The fiberglass roof problem is also common in marine VHF (156-163Mhz)
installations. Those tend to use 1/2 wave antennas, which do not
require a ground plane. The automobile version of the 1/2 wave:
http://www.theantennafarm.com/catalog/laird-tech-bb1322w-4470.html?zenid=6bc9236b727ed1e483c9037fb2ac52db




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article ,
Jeff Liebermann wrote:

I overlooked the mobile operation from a car. Of course, when the
antenna is mounted on a metal surface, you don't need radials..

If it's a metal car roof, you don't need radials. Unfortunately, I've
had to deal with verhicles that have a fiberglass roof. Aluminum duct
tape ground plane (on the inside) to the rescue.

That will help but not entirely resolve the situation.

What I have heard, is that the theoretical gain advantage of a
5/8-wavelength monopole over a 1/4-wave monopole, is dependent on the
antenna being operated over a fairly large groundplane (one which
reaches out several wavelengths from the feedpoint). A simple set of
ground-radial "tapes" won't be big or extensive enough... and,
actually, neither will be the typical vehicle roof (at VHF wavelengths
at least).

According to these sources, in the absence of a good groundplane, the
5/8-wave monopole tends to "squint" - its highest-gain lobes are not
towards the horizon but aim upwards somewhat. Gain towards the
horizon may be *less* than a quarter-wave monopole on the same vehicle
mount.

So, the theoretical gain advantage of a 5/8-wave vehicle antenna may
not work out in practice. Testing would be required to see if there's
actually an advantage, or whether a "high gain" antenna of this sort
is actually a loss in practice because the gain is aimed in the wrong
directions.

And, I agree that for many vehicle mounting situations, a "ground
independent" antenna such as an end-fed half-wave may be the best bet.
I believe you can get these in a shortened form (with distributed or
lumped inductive loading in the center of the radiator) to keep the
height within reason... but going for a full-length end-fed radiator
would give you somewhat better gain and efficiency, if it's safe to
install on the vehicle.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Mon, 24 Jun 2013 11:04:01 -0700, (Dave Platt)
wrote:

In article ,
Jeff Liebermann wrote:

I overlooked the mobile operation from a car. Of course, when the
antenna is mounted on a metal surface, you don't need radials..

If it's a metal car roof, you don't need radials. Unfortunately, I've
had to deal with verhicles that have a fiberglass roof. Aluminum duct
tape ground plane (on the inside) to the rescue.

That will help but not entirely resolve the situation.

What I have heard, is that the theoretical gain advantage of a
5/8-wavelength monopole over a 1/4-wave monopole, is dependent on the
antenna being operated over a fairly large groundplane (one which
reaches out several wavelengths from the feedpoint). A simple set of
ground-radial "tapes" won't be big or extensive enough... and,
actually, neither will be the typical vehicle roof (at VHF wavelengths
at least).

Umm... if that were true, then 5/8 wave base station antennas, which
all have 1/4 wave ground radials, shouldn't work or require extra long
ground radials. Here's a stacked dual 5/8 wave 6 meter ground plane
antenna:
http://802.11junk.com/jeffl/antennas/gnd-plane-05/index.html
(Note that the characteristic impedance is about 125 ohms and that the
necessary matching xformer is not shown). Plenty more 5/8 wave base
stations antennas with 1/4 wave radials found with Google images:
https://www.google.com/search?q=5/8+wave+base+station+antenna&tbm=isch


However, I will confess that the aluminum duct tape ground plane was
easy. The fiberglass roof had stiffener ridges, projecting lamps,
other antennas, and metal stiffeners. Wiggling the tape around these
was not easy. I finally gave up, dropped the entire headline, removed
all the other hardware, and covered most of the roof with the foil
tape. It wasn't an electrical issue, but rather that we didn't have
time to do much experimenting. There was no reason to minimize the
use of the aluminum duct tape, so I just plastered it onto the
underside wherever possible. I therefore did NOT determine if 1/4
wave radials were adequate. Also, no swept response with an antenna
analyzer... just a VSWR check.

According to these sources, in the absence of a good groundplane, the
5/8-wave monopole tends to "squint" - its highest-gain lobes are not
towards the horizon but aim upwards somewhat. Gain towards the
horizon may be *less* than a quarter-wave monopole on the same vehicle
mount.

I would think it would be the other way around. Large ground planes
are more reflective causing more of the RF to go towards the sky. I'll
need to run an NEC2 model to be sure. However, at VHF, I don't think
it's a problem. The vertical radiation angle of a 5/8 wave antenna is
sufficiently wide that a small change in takeoff angle isn't going to
make much of a difference in coverage.

End fed collinear antennas, with or without a ground plane, usually
have a non-zero takeoff angle. If you want the major lobe to point to
the horizon (i.e. zero takeoff angle), the antenna should be center
fed, which is not going to happen on a mobile antenna. However,
that's not necessarily a good thing, as such a wide vertical radiation
angle antenna, that is so close to the ground, is going to send much
of the RF into the absorbent ground. Better to have some uptilt and
hope that some of it goes in the right direction.

So, the theoretical gain advantage of a 5/8-wave vehicle antenna may
not work out in practice. Testing would be required to see if there's
actually an advantage, or whether a "high gain" antenna of this sort
is actually a loss in practice because the gain is aimed in the wrong
directions.

That doesn't sound like it would be easy to test on a vehicle. I
think a computer model might be easier and probably more interesting.
(No, I'm not volunteering to do one).

And, I agree that for many vehicle mounting situations, a "ground
independent" antenna such as an end-fed half-wave may be the best bet.

Yep. I have quite a bit of experience with 1/2 wave antennas on
fiberglass vessels. They work just fine. However, there's an
additional problem on marine applications which limits antennas to
fairly low gains. If the gain is too high, and the vessel rocks and
rolls with the waves, the narrow radiation angle could easily send the
signal into the sky or into the water, instead of towards the horizon.
There's a similar problem in vehicles going up and down hills, but is
less serious. Fortunately, for VHF, it's not too horrible.

I believe you can get these in a shortened form (with distributed or
lumped inductive loading in the center of the radiator) to keep the
height within reason... but going for a full-length end-fed radiator
would give you somewhat better gain and efficiency, if it's safe to
install on the vehicle.

Yep.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

It would have helped - had the OP posted the model number for the antenna and a description of what he wanted to do with it.

A mobile vertical antenna has no gain - gain is only achieved when you have gain in one direction and rejection in one or more directions.

The only measurable gain would be gain as compared to a dipole or gain over isotropic.

1/4 wave antenna's can sometimes produce a better signal locally, because the radiation pattern is spread out over a larger area.

It will give no distance gain - just local reception.]

Because it is all one radio - the reception length does not matter, just that it is resonant at X mhz - transmit.

Public service here all uses Larsen antenna's - especially the PA State Police, and they have very deep pockets.

Shakespeare also makes a decent mobile antenna.

You need a antenna analyzer or a Dip Meter to set to resonance.

The only thing the SWR meter can do is tell you what is happening in the feed line.

On Wed, 26 Jun 2013 13:16:39 +0100, Channel Jumper
wrote:

A mobile vertical antenna has no gain - gain is only achieved when you
have gain in one direction and rejection in one or more directions.

Wrong. Gain on a mobile antenna can be achieved without
directionality. Just reduce the vertical radiation angle, which puts
more RF towards the horizon, and less RF towards the sky and the
ground.

The only measurable gain would be gain as compared to a dipole or gain
over isotropic.

Yep. That's the way gain is normally measured. dBd or dBi.

1/4 wave antenna's can sometimes produce a better signal locally,
because the radiation pattern is spread out over a larger area.

I've seen that. However, it's usually the result of misusing a "gain"
type antenna, such as a dual band 5/8 ham antenna being used on marine
or commercial frequencies, or a 5/8 commercial antenna, being used on
ham frequencies. Lots of ways to do it wrong. Where a 1/4 wave
antenna really shines is when one needs to cover a wide range of VHF
frequencies, from aircraft to marine.

It will give no distance gain - just local reception.]

Ummm... the range depends more on the terrain than on the antenna.

Because it is all one radio - the reception length does not matter, just
that it is resonant at X mhz - transmit.

VSWR is highly over-rated. The only real reason to keep VSWR low is
that high VSWR will cause the transmitter to protect itself and partly
shut down.

Try this experiment. Take a piece of sheet metal (or aluminum foil
covered cardboard) to act as a ground plane. Insert and SO-239
connector in the middle. Add a length of moderately stiff electrical
wire to the SO-239 that is longer than 1/4 wave at the weather
frequency (162.xxxx). Find a receiver that will measure the actual
receive signal strength. An all mode or AM (not FM) receiver will
work nicely. Extra credit for using a service monitor. Make a
measurement and start cutting the length of the antenna in roughly
1/2" intervals. Measure the receive signal strength.

What I've found when I've done this, is that the antenna gain, which
is what the receive signal level indicates, doesn't change very much
until you get down to about 1/8th wavelength. I modeled this test
using 4NEC2 and found the same thing.

Now, if you believe that the tx and rx performance of an antenna are
identical, this would suggest that you could make the antenna almost
any length, and still have adequate gain and function if you could fix
the VSWR.

Public service here all uses Larsen antenna's - especially the PA State
Police, and they have very deep pockets.

Obviously, the more expensive the antenna, the better it works.

Shakespeare also makes a decent mobile antenna.

They mostly make marine and military antennas. Their commercial
antennas are overpriced versions of the antennas that they sell to the
military. They're very well built, rugged, but not cheap.
http://shakespeare-military.com

You need a antenna analyzer or a Dip Meter to set to resonance.

Have you ever tried to resonate a 1/4 wave antenna with either of
those? You'll find that it's affected by the position and location of
just about everything within about a 20 ft radius. I run a sweep
generator, directional coupler, detector, and scope combination to
test antennas, but no way would I ever use that to tune the antenna.
Just getting near the antenna ruins the display. Incidentally, for
complex antennas, such as a dual band J-pole, minimum VSWR isn't
always at resonance.

The only thing the SWR meter can do is tell you what is happening in the
feed line.

Wrong. A VSWR meter reading is affected by the xmitter output
impedance, feed line impedance to the VSWR meter, characteristic
impedance of the coax cables(s), feed line impedance after the VSWR
meter, and of course, the antenna impedance. That's actually a
problem because a VSWR meter is affected by literally everything.

Drivel: I run mostly 75 ohm systems (because the coax is cheap and
easy and has less loss). I had to build my own 75 ohm directional
coupler in order to get accurate VSWR measurements. (Yes, Bird makes
a 75 ohm wattmeter 4307, but I don't want to spend the money).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

And so Jeff speaks.

Jeff - the radiation pattern of a 1/4 wave antenna pancakes compared to a longer antenna, but you cannot use weather radio as a barometer to measure how efficient a antenna works.

Weather radio is broadcast in such a way that a signal is available to most people within a 40 mile radius circle from each transmitter - at least in Western Pennsylvania. The signals here - about 350 watts at the transmitter - is enough that a simple table top radio or a cheap bubble pack GMRS radio will usually receive it - even with a 4 inch antenna.

However - when working any type of DX - you best better bring your A game or go home. You are not going to net much with a simple 1/4 wave antenna on VHF frequencies when the bands are not wide open.

This man wants to replace his mobile antenna with something better, but does not want to take the advice of his radio technician - because he thinks the guy is ripping him off.

The bottom line is - most people involved in communications doesn't just start selling radios without any type of formal education.
Even if the only education the person received was from the Military, it is usually based on sound practices and principals.

I don't usually deal with anyone that carries their money in a snapper purse.

If someone wants to tell me how to do something that I have been doing for 40 years - I just walk away.
I laugh at these so called roadside CB radio shops that sells all this garbage to these CB radio guys, including their peek n tunes - which does nothing except reduce the life of the radio.

Good Catch Jeff, and thanks for straightening thins out -- it's amazing
some of the things we think we know about antennas and antenna measurement
until someone corrects us!
Furthermore, it's difficult for someone who does not fully understand the
concepts to receive
misinformation!

Irv VE6BP

"Jeff Liebermann" wrote in message
...
On Wed, 26 Jun 2013 13:16:39 +0100, Channel Jumper
wrote:

A mobile vertical antenna has no gain - gain is only achieved when you
have gain in one direction and rejection in one or more directions.

Wrong. Gain on a mobile antenna can be achieved without
directionality. Just reduce the vertical radiation angle, which puts
more RF towards the horizon, and less RF towards the sky and the
ground.

The only measurable gain would be gain as compared to a dipole or gain
over isotropic.

Yep. That's the way gain is normally measured. dBd or dBi.

1/4 wave antenna's can sometimes produce a better signal locally,
because the radiation pattern is spread out over a larger area.

I've seen that. However, it's usually the result of misusing a "gain"
type antenna, such as a dual band 5/8 ham antenna being used on marine
or commercial frequencies, or a 5/8 commercial antenna, being used on
ham frequencies. Lots of ways to do it wrong. Where a 1/4 wave
antenna really shines is when one needs to cover a wide range of VHF
frequencies, from aircraft to marine.

It will give no distance gain - just local reception.]

Ummm... the range depends more on the terrain than on the antenna.

Because it is all one radio - the reception length does not matter, just
that it is resonant at X mhz - transmit.

VSWR is highly over-rated. The only real reason to keep VSWR low is
that high VSWR will cause the transmitter to protect itself and partly
shut down.

Try this experiment. Take a piece of sheet metal (or aluminum foil
covered cardboard) to act as a ground plane. Insert and SO-239
connector in the middle. Add a length of moderately stiff electrical
wire to the SO-239 that is longer than 1/4 wave at the weather
frequency (162.xxxx). Find a receiver that will measure the actual
receive signal strength. An all mode or AM (not FM) receiver will
work nicely. Extra credit for using a service monitor. Make a
measurement and start cutting the length of the antenna in roughly
1/2" intervals. Measure the receive signal strength.

What I've found when I've done this, is that the antenna gain, which
is what the receive signal level indicates, doesn't change very much
until you get down to about 1/8th wavelength. I modeled this test
using 4NEC2 and found the same thing.

Now, if you believe that the tx and rx performance of an antenna are
identical, this would suggest that you could make the antenna almost
any length, and still have adequate gain and function if you could fix
the VSWR.

Public service here all uses Larsen antenna's - especially the PA State
Police, and they have very deep pockets.

Obviously, the more expensive the antenna, the better it works.

Shakespeare also makes a decent mobile antenna.

They mostly make marine and military antennas. Their commercial
antennas are overpriced versions of the antennas that they sell to the
military. They're very well built, rugged, but not cheap.
http://shakespeare-military.com

You need a antenna analyzer or a Dip Meter to set to resonance.

Have you ever tried to resonate a 1/4 wave antenna with either of
those? You'll find that it's affected by the position and location of
just about everything within about a 20 ft radius. I run a sweep
generator, directional coupler, detector, and scope combination to
test antennas, but no way would I ever use that to tune the antenna.
Just getting near the antenna ruins the display. Incidentally, for
complex antennas, such as a dual band J-pole, minimum VSWR isn't
always at resonance.

The only thing the SWR meter can do is tell you what is happening in the
feed line.

Wrong. A VSWR meter reading is affected by the xmitter output
impedance, feed line impedance to the VSWR meter, characteristic
impedance of the coax cables(s), feed line impedance after the VSWR
meter, and of course, the antenna impedance. That's actually a
problem because a VSWR meter is affected by literally everything.

Drivel: I run mostly 75 ohm systems (because the coax is cheap and
easy and has less loss). I had to build my own 75 ohm directional
coupler in order to get accurate VSWR measurements. (Yes, Bird makes
a 75 ohm wattmeter 4307, but I don't want to spend the money).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 6/26/2013 10:17 AM, Jeff Liebermann wrote:
On Wed, 26 Jun 2013 13:16:39 +0100, Channel Jumper
wrote:

A mobile vertical antenna has no gain - gain is only achieved when you
have gain in one direction and rejection in one or more directions.

Wrong. Gain on a mobile antenna can be achieved without
directionality. Just reduce the vertical radiation angle, which puts
more RF towards the horizon, and less RF towards the sky and the
ground.

The only measurable gain would be gain as compared to a dipole or gain
over isotropic.

Yep. That's the way gain is normally measured. dBd or dBi.

1/4 wave antenna's can sometimes produce a better signal locally,
because the radiation pattern is spread out over a larger area.

I've seen that. However, it's usually the result of misusing a "gain"
type antenna, such as a dual band 5/8 ham antenna being used on marine
or commercial frequencies, or a 5/8 commercial antenna, being used on
ham frequencies. Lots of ways to do it wrong. Where a 1/4 wave
antenna really shines is when one needs to cover a wide range of VHF
frequencies, from aircraft to marine.

It will give no distance gain - just local reception.]

Ummm... the range depends more on the terrain than on the antenna.

Because it is all one radio - the reception length does not matter, just
that it is resonant at X mhz - transmit.

VSWR is highly over-rated. The only real reason to keep VSWR low is
that high VSWR will cause the transmitter to protect itself and partly
shut down.

Try this experiment. Take a piece of sheet metal (or aluminum foil
covered cardboard) to act as a ground plane. Insert and SO-239
connector in the middle. Add a length of moderately stiff electrical
wire to the SO-239 that is longer than 1/4 wave at the weather
frequency (162.xxxx). Find a receiver that will measure the actual
receive signal strength. An all mode or AM (not FM) receiver will
work nicely. Extra credit for using a service monitor. Make a
measurement and start cutting the length of the antenna in roughly
1/2" intervals. Measure the receive signal strength.

What I've found when I've done this, is that the antenna gain, which
is what the receive signal level indicates, doesn't change very much
until you get down to about 1/8th wavelength. I modeled this test
using 4NEC2 and found the same thing.

Now, if you believe that the tx and rx performance of an antenna are
identical, this would suggest that you could make the antenna almost
any length, and still have adequate gain and function if you could fix
the VSWR.



I do not doubt your information here. However, it seems to conflict with
my experiences working 75 meters. I work 75 each day using a 75 meter
horizontal loop. I hear the same characters on each day. Often a newbie
pops up with a poor signal. He is in the same area as "the gang" and yet
his signal stinks. Almost invariably we ask him about his G5RV. "Gee
guys how did you know I was using a G5RV?" Poor signals shows up every
time. He is using a dipole that is way too short to resonate on 75
meters. I think they are 82 feet long. It seems to me if VSWR made
little difference, then his 82 foot long dipole on 75 meters should work
just fine. Not trying for a fight, just want an opinion about why we are
hearing this effect. Of course they are using tuners to make a match to
their transceivers.


My own loop is carefully cut for 3.9 mhz. I need a tuner because it is
feed with 600 ohm open wire line and has a nasty VSWR because of
mismatch between the lead-in and antenna. The online calculator for loss
using my antenna system comes out to be 1/2 db. I can live with that.
However, if I put up a loop that was 1/2 the size I need, and then
matched it with a tuner, it would hardly work at all. I know. I tried
loading mine on 160 meters. I could make a match with the tuner. But it
was a bust.

Public service here all uses Larsen antenna's - especially the PA State
Police, and they have very deep pockets.

Obviously, the more expensive the antenna, the better it works.

Shakespeare also makes a decent mobile antenna.

They mostly make marine and military antennas. Their commercial
antennas are overpriced versions of the antennas that they sell to the
military. They're very well built, rugged, but not cheap.
http://shakespeare-military.com

You need a antenna analyzer or a Dip Meter to set to resonance.

Have you ever tried to resonate a 1/4 wave antenna with either of
those? You'll find that it's affected by the position and location of
just about everything within about a 20 ft radius. I run a sweep
generator, directional coupler, detector, and scope combination to
test antennas, but no way would I ever use that to tune the antenna.
Just getting near the antenna ruins the display. Incidentally, for
complex antennas, such as a dual band J-pole, minimum VSWR isn't
always at resonance.

The only thing the SWR meter can do is tell you what is happening in the
feed line.

Wrong. A VSWR meter reading is affected by the xmitter output
impedance, feed line impedance to the VSWR meter, characteristic
impedance of the coax cables(s), feed line impedance after the VSWR
meter, and of course, the antenna impedance. That's actually a
problem because a VSWR meter is affected by literally everything.

Drivel: I run mostly 75 ohm systems (because the coax is cheap and
easy and has less loss). I had to build my own 75 ohm directional
coupler in order to get accurate VSWR measurements. (Yes, Bird makes
a 75 ohm wattmeter 4307, but I don't want to spend the money).

El lunes, 24 de junio de 2013 20:04:01 UTC+2, Dave Platt escribió:
In article ,

Jeff Liebermann wrote:



I overlooked the mobile operation from a car. Of course, when the

antenna is mounted on a metal surface, you don't need radials..



If it's a metal car roof, you don't need radials. Unfortunately, I've

had to deal with verhicles that have a fiberglass roof. Aluminum duct

tape ground plane (on the inside) to the rescue.



That will help but not entirely resolve the situation.



What I have heard, is that the theoretical gain advantage of a

5/8-wavelength monopole over a 1/4-wave monopole, is dependent on the

antenna being operated over a fairly large groundplane (one which

reaches out several wavelengths from the feedpoint). A simple set of

ground-radial "tapes" won't be big or extensive enough... and,

actually, neither will be the typical vehicle roof (at VHF wavelengths

at least).



According to these sources, in the absence of a good groundplane, the

5/8-wave monopole tends to "squint" - its highest-gain lobes are not

towards the horizon but aim upwards somewhat. Gain towards the

horizon may be *less* than a quarter-wave monopole on the same vehicle

mount.



So, the theoretical gain advantage of a 5/8-wave vehicle antenna may

not work out in practice. Testing would be required to see if there's

actually an advantage, or whether a "high gain" antenna of this sort

is actually a loss in practice because the gain is aimed in the wrong

directions.



And, I agree that for many vehicle mounting situations, a "ground

independent" antenna such as an end-fed half-wave may be the best bet.

I believe you can get these in a shortened form (with distributed or

lumped inductive loading in the center of the radiator) to keep the

height within reason... but going for a full-length end-fed radiator

would give you somewhat better gain and efficiency, if it's safe to

install on the vehicle.



--

Dave Platt AE6EO

Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior

I do _not_ wish to receive unsolicited commercial email, and I will

boycott any company which has the gall to send me such ads!

To Jeff and Dave,

I agree on the end-fed half-wave. I like them but you need to take care of matching and good capacitors (high voltage breakdown).

The myth of the gain advantage of the 5/8lambda is from the AM broadcast antenna patterns where we have a large ground plane (mother earth, I am sure you both know).

I fully agree; the half-wave, and even the quarter-wave will win with real world ground planes/radials on HF/VHF/UHF terrestrial links. As long as people think "longer = better", the myth will continue and peoople keep buying 5/8 lambda verticals with radials (the pigeons like them!).

To avoid long discussion with others: I know stacking with good phasing does help to increase gain.

Wim
PA3DJS
please instruct your racing pigeon to skip abc.