Because the reports about this antenna, and antennas like these, are
classic
examples of the 'miracle miniature' syndrome that plagues antenna
manufacturers
in their fierce competition. Unlike other industries, they don't have to
back up
their claims of gain figures, which is why you see ads for rubber duckies
with
+126 dB gain.

Entirely reasonable, provided they tell you what the reference is.
A claim of "5 dB gain" is meaningless. In ham circles, when I see this, I
automatically assume they mean dBi, but given the level of snake oil in CB
circles, I think in terms of dBdummyload.

An interesting test would be to measure two of the same antenna, against
each other, on the same vehicle, then measure the first one again. Of
course the readings should be identical, but differences would indicate
problems in mounting most likely, or variations in local conditions, like
reflected signal from vehicles and people moving around. It would give a
good idea of the size of the inherent error in the measurements made.

In order to truly show what's going on, you also need to pattern the
antenna, measuring the signal at regular points around the compass. While an
onmi antenna mounted on a vehicle may show gain in one direction, there will
be a corresponding notch somewhere else. The pattern, when mounted on a
vehicle, can be surprisingly "lumpy".

In order to do a reasonably accurate test, you'll need a nice RF quiet area
to test in, and a whole lot of open space. Ideally, you'd put the vehicle
on a turntable, but that's normally not practical.
I'd settle for very slowly driving in as tight a circle as possible, to
minimize effects from the antenna waving around.


- Probably the biggest problem with Tnom's "test" was that there was no
impedance matching from the coax to the antenna. Loaded antennas usually
have a
lower feedpoint impedance, resulting in a larger mismatch (higher SWR).

Another variable to consider, is wether they were tuned at all, and if so,
were they tuned for resonance, or lowest SWR. I tune for resonance, and
match for SWR.

The problem here is that if the radio and antenna are not properly grounded
(and a
mag-mount is -not- a proper ground), the SWR meter isn't going to show
that
mismatch unless the meter is connected at the antenna feedpoint, which was
not
the case (and wouldn't have mattered anyway because the antenna was not
properly
grounded). He might have caught the problem had he measured and compared
the
forward power of all the antennas, but he didn't because he felt is was
"not
needed".

A 1 wavelength feedline, of something reasonably efficient like FSJ1-50
would suffice.
The reactive component will be roated back around to the same point, and
it's way more convenient than measuring at the base of the antenna.

- Bandwidth was never measured. The coils on that antenna should have a
very
high Q, which means a very narrow bandwidth. If the test showed that the
antenna
actually has a wide bandwidth, then there is some power being dumped
somewhere
as heat and not RF, probably from a resistor hidden somewhere in the
shaft, and
most likely the shaft inside the coil, shunting the coil and lowering it's
Q.

Important, and easy to do. Impedance measurements at Ch1 and CH40 would
tell the story.

- The concept of center-loading an antenna has been around for a very long
time.
If it were at all possible to shorten a 1/4 wave vertical and get better
performance, the design would have been implemented into AM broadcast
towers
decades ago. Drive around and look at some of the towers in your area. How
many
of them look like the X-terminator? None.

To be fair, fabricating the coils for such an antenna would be an
interesting challenge.


I run a cobra 6000, which seems a reasonable design. It's mounted in the
center of the roof of my Expedition, and just slightly taller than the
Diamond SG-7900 in front of it. Overall height is somewhat of a concern.
It tunes to resonance nicely, and ends up at a 2/1 SWR, which isn't far
enough off to bother matching.. If I had a 2-1 un-un handy, I'd probably use
it. I'm not too surprised at the high impedance (100 ohms) at resonance, I
think they are designed to be used in a co-phased arraingement on trucks.

There's another typical sight, a pair of antennas, often not the same type,
running "co-phased" on a very small car, placed much too close together,
like 2' separation. The resulting pattern is rather amusing.


I run into the same BS on the other end of the spectrum.

I recently had to look into antennas for a bluetooth transciever, and was
rather dissapointed to find the equivalent of "rubber ducks" at 2.4 GHz,
selling for $12. (in production quantities!) These are so called "chip
antennas" that are roughly the size of this letter "W" on your screen, being
marketed as "high gain" antennas. When I finally was able to get a plot out
of them, it turned out that the highest gain was -10dBi, and as low
as -20dBi...
High gain compared to a 50 ohm resistor the same size, I suppose.

We ended up using a simple monopole, just a track on the PCB. Cost,
essentially zero.
Gain, roughly 1-2dBi. I didn't bother patterning, simple emperical tests
show it's overkill for our intended application. It's giving measurably
less operating distance than a reference dipole, but the dipole is
inconveniently large.

Now if you still want to buy the antenna, it's your money to waste. But
who
knows... it might have some collector value in a hundred years or so, just
like
all those quack medical devices.

My favorite CB gimmick was the "zing ring". You were supposed to clamp this
little halo around the bottom of your antenna to improve the ground. The
thing had a radius of about 6 inches or so.
It wouldn't even have had that effect up on VHF, where it's dimensions
become a significant fraction of a wavelength. Lately the Zing Ring is
gone, replaced with three little stubby wound whips that connect to the base
of the antenna electrically.. The new version looks better anyway.. I'm
sure it's just as effective as the old one.

You have to laugh at the concept of a "15,000 Watt" antenna, on a mag-mount,
fed with cheap RG-58 sized coax.

These antenna gimmicks are all 100% effective in meeting their design goals.
They look good enough to separate suckers and their money.
Any benefit to your radiation efficiency or pattern is totally coincidental.

In , "Dave VanHorn"
wrote:


Because the reports about this antenna, and antennas like these, are
classic
examples of the 'miracle miniature' syndrome that plagues antenna
manufacturers
in their fierce competition. Unlike other industries, they don't have to
back up
their claims of gain figures, which is why you see ads for rubber duckies
with
+126 dB gain.

Entirely reasonable, provided they tell you what the reference is.
A claim of "5 dB gain" is meaningless. In ham circles, when I see this, I
automatically assume they mean dBi, but given the level of snake oil in CB
circles, I think in terms of dBdummyload.

.....or dB over the transmission line.

An interesting test would be to measure two of the same antenna, against
each other, on the same vehicle, then measure the first one again. Of
course the readings should be identical, but differences would indicate
problems in mounting most likely, or variations in local conditions, like
reflected signal from vehicles and people moving around. It would give a
good idea of the size of the inherent error in the measurements made.

I agree. In order to exclude such confounds the control or reference antenna
should be measured several times and any variation noted, even any variation
during a single transmission.

In order to truly show what's going on, you also need to pattern the
antenna, measuring the signal at regular points around the compass. While an
onmi antenna mounted on a vehicle may show gain in one direction, there will
be a corresponding notch somewhere else. The pattern, when mounted on a
vehicle, can be surprisingly "lumpy".

That's called "mapping the contour". It's not difficult to do, and is a basic
procedure for any antenna testing. In fact, it's a procedure that is required
before any broadcast station can get it's license, as the map is used to
calculate the ERP of the transmitter.

In order to do a reasonably accurate test, you'll need a nice RF quiet area
to test in, and a whole lot of open space. Ideally, you'd put the vehicle
on a turntable, but that's normally not practical.
I'd settle for very slowly driving in as tight a circle as possible, to
minimize effects from the antenna waving around.

The salt flats in Utah come to mind, but we have some pretty flat desert areas
just west of here.

- Probably the biggest problem with Tnom's "test" was that there was no
impedance matching from the coax to the antenna. Loaded antennas usually
have a
lower feedpoint impedance, resulting in a larger mismatch (higher SWR).

Another variable to consider, is wether they were tuned at all, and if so,
were they tuned for resonance, or lowest SWR. I tune for resonance, and
match for SWR.

That's fine and practical for one antenna, but when comparing several where
different input impedances will be encountered, the method of tuning should be
independant of input Z. About the only way to do that is with an FSM. After all,
a 50 ohm dummy load will show a 1:1 SWR.....

The problem here is that if the radio and antenna are not properly grounded
(and a
mag-mount is -not- a proper ground), the SWR meter isn't going to show
that
mismatch unless the meter is connected at the antenna feedpoint, which was
not
the case (and wouldn't have mattered anyway because the antenna was not
properly
grounded). He might have caught the problem had he measured and compared
the
forward power of all the antennas, but he didn't because he felt is was
"not
needed".

A 1 wavelength feedline, of something reasonably efficient like FSJ1-50
would suffice.
The reactive component will be roated back around to the same point, and
it's way more convenient than measuring at the base of the antenna.

The problem there is that the feedline may be radiating when there is a mismatch
at the antenna. Regardless, he never indicated the length of the coax -or- if
the coax was tested for RF on the shield.

- Bandwidth was never measured. The coils on that antenna should have a
very
high Q, which means a very narrow bandwidth. If the test showed that the
antenna
actually has a wide bandwidth, then there is some power being dumped
somewhere
as heat and not RF, probably from a resistor hidden somewhere in the
shaft, and
most likely the shaft inside the coil, shunting the coil and lowering it's
Q.

Important, and easy to do. Impedance measurements at Ch1 and CH40 would
tell the story.

Three points (freqs) would be better, as it will verify that the frequency
response is curved and not flat (resistive).

- The concept of center-loading an antenna has been around for a very long
time.
If it were at all possible to shorten a 1/4 wave vertical and get better
performance, the design would have been implemented into AM broadcast
towers
decades ago. Drive around and look at some of the towers in your area. How
many
of them look like the X-terminator? None.

To be fair, fabricating the coils for such an antenna would be an
interesting challenge.

True. But in broadcasting, efficiency is everything. If that antenna design
worked better than the basic tower, the justification would be the long-term
power savings to the station. And with all the stations that are operating these
days, don't you think at least one station would have built such an antenna?

I run a cobra 6000, which seems a reasonable design. It's mounted in the
center of the roof of my Expedition, and just slightly taller than the
Diamond SG-7900 in front of it. Overall height is somewhat of a concern.
It tunes to resonance nicely, and ends up at a 2/1 SWR, which isn't far
enough off to bother matching.. If I had a 2-1 un-un handy, I'd probably use
it. I'm not too surprised at the high impedance (100 ohms) at resonance, I
think they are designed to be used in a co-phased arraingement on trucks.

You may be getting reflection from the other antenna. Try tuning without the
other stick.

There's another typical sight, a pair of antennas, often not the same type,
running "co-phased" on a very small car, placed much too close together,
like 2' separation. The resulting pattern is rather amusing.

I saw a Penetrator on a Geo once.....

I run into the same BS on the other end of the spectrum.

I recently had to look into antennas for a bluetooth transciever, and was
rather dissapointed to find the equivalent of "rubber ducks" at 2.4 GHz,
selling for $12. (in production quantities!) These are so called "chip
antennas" that are roughly the size of this letter "W" on your screen, being
marketed as "high gain" antennas. When I finally was able to get a plot out
of them, it turned out that the highest gain was -10dBi, and as low
as -20dBi...
High gain compared to a 50 ohm resistor the same size, I suppose.

Didn't someone come out with some sort of quack antenna for cell phones? I
thought I saw that on a TV commercial or something....

We ended up using a simple monopole, just a track on the PCB. Cost,
essentially zero.
Gain, roughly 1-2dBi. I didn't bother patterning, simple emperical tests
show it's overkill for our intended application. It's giving measurably
less operating distance than a reference dipole, but the dipole is
inconveniently large.

Now if you still want to buy the antenna, it's your money to waste. But
who
knows... it might have some collector value in a hundred years or so, just
like
all those quack medical devices.

My favorite CB gimmick was the "zing ring". You were supposed to clamp this
little halo around the bottom of your antenna to improve the ground. The
thing had a radius of about 6 inches or so.
It wouldn't even have had that effect up on VHF, where it's dimensions
become a significant fraction of a wavelength. Lately the Zing Ring is
gone, replaced with three little stubby wound whips that connect to the base
of the antenna electrically.. The new version looks better anyway.. I'm
sure it's just as effective as the old one.

Sounds like these "tuning rings" on some current antennas.

You have to laugh at the concept of a "15,000 Watt" antenna, on a mag-mount,
fed with cheap RG-58 sized coax.

These antenna gimmicks are all 100% effective in meeting their design goals.
They look good enough to separate suckers and their money.
Any benefit to your radiation efficiency or pattern is totally coincidental.

The thought of 15 KW on a vehicle makes me shudder -- knowing that the vehicle
itself is carrying the same voltage and current as the antenna, but terminated
with a gas tank!!!!








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Entirely reasonable, provided they tell you what the reference is.
A claim of "5 dB gain" is meaningless. In ham circles, when I see this,
I
automatically assume they mean dBi, but given the level of snake oil in
CB
circles, I think in terms of dBdummyload.

....or dB over the transmission line.

dBradiax?




The problem there is that the feedline may be radiating when there is a
mismatch
at the antenna. Regardless, he never indicated the length of the coax -or-
if
the coax was tested for RF on the shield.

This is why I pay $2000/Day to my FCC testing guys. It's not as simple as
it looks!


You may be getting reflection from the other antenna. Try tuning without
the other stick.

That's my primary radio. I use the CB for road conditions, but if one of
them has to compromise..


Didn't someone come out with some sort of quack antenna for cell phones? I
thought I saw that on a TV commercial or something....

Yeah, the "patch" to get your yangtenna up.
I got one free in a parts order once. It's worth at least twice what I paid
for it.
I did give it a fair trial. No noticable effect one way or the other.



Sounds like these "tuning rings" on some current antennas.

The tuning ring on an Astron 99 or similar at least does something.
I use one of those as my HF vertical.

The zing ring was the "cell phone antenna sticker" of it's day.


The thought of 15 KW on a vehicle makes me shudder

Figuring a generous 60% efficiency at the amp, that's 1800A from your
battery, more or less.

You know, I've always known that power dosen't count for much on these
bands, and as I was driving back from Georgia again this weekend, I remarked
to the wife that listening to the truckers fade in and out going the other
direction, I can't tell much difference between the guy that claims he's
running the 150W or 500W amplifier, and the ones that claim not to be..

I certainly don't hear them 20-50 miles away..

-- knowing that the vehicle
itself is carrying the same voltage and current as the antenna, but
terminated
with a gas tank!!!!

Back an August, I was sitting at a gas station fueling up the Expedition,
which does take a while..
I was sitting there, with my 50W aprs transmitter running periodically (on
the glassmount antenna right above the gas tank), the other two VHF
transcievers were shut down. I was making a call on my cell phone, when I
noticed that the truck parked in the next bay was idling, and dripping
something that was spattering on the concrete... The truck was labeled
"liquid oxygen", and "no smoking within 50 feet".. As the cold liquid
oxygen vapor mixed with the gasoline vapor hugging the ground, I was
thinking "and they are worried about my cell phone?"

You make valid points on testing antennas, It would be great to have
actual tests that were run with all variables being accounted for.
Looking
at the way he did his tests, is more real world. That is, the way a
typical person would do when the purchased an antenna and put it on their
vehicle. His tests show which one worked best for the testing he was
doing. Which would probably have different results on someone elses
installation.

The trick is to get a feel for the magnitude of the variables that are hard
to control, and take that into account when evaluating any measured or
perceived differences.

The audiophile guys are buying $7500 AC line cords because they think that
it makes a difference in how the sound comes out. (ignoring the same old 50'
of crappy 12 ga wire in the wall back to the box, and the rest of how the
power gets to the house)

"Landshark" wrote:

"(Scott Unit 69)" wrote in message
...

You are wrong.

"Landshark" wrote:
Forge

"(Scott Unit 69)" wrote in message
...


Nope, you're not Scott. Try all you want,
but you are forging his name, posting from
AOL through put, using Ghostsearchers website.

Landshark

Well I am sorry but you are wrong. Since I got my ham license I use Ghostsearchers
on Usenet so I don't crap up my regular ISP with spam and trash from rrcb.

I think the only thing proven with his experiment is that a good antenna
can
work just as crappy as a crappy antenna -- the only difference is in the
installation. Radio requires attention to several factors, such as knowing
the
difference between an RF ground and a DC ground, how SWR and
field-strength
meters really work and how to use them, using the right equipment for the
right
job, location of the antenna on the vehicle, etc, etc. And BTW, these are
things
that should be learned and put into practice by anyone serious about the
hobby.

You wouldn't believe (maybe you would, at that) how many hams I know, that
think a 6' wire to a ground stake is an RF ground for their VHF/UHF
station..

On Tue, 28 Oct 2003 15:40:01 -0500, "Dave VanHorn"
wrote:


I think the only thing proven with his experiment is that a good antenna
can
work just as crappy as a crappy antenna -- the only difference is in the
installation. Radio requires attention to several factors, such as knowing
the
difference between an RF ground and a DC ground, how SWR and
field-strength
meters really work and how to use them, using the right equipment for the
right
job, location of the antenna on the vehicle, etc, etc. And BTW, these are
things
that should be learned and put into practice by anyone serious about the
hobby.

You wouldn't believe (maybe you would, at that) how many hams I know, that
think a 6' wire to a ground stake is an RF ground for their VHF/UHF
station..


I believe quite a few would believe that on HF, but VHF/UHF. What do
you think would make a good RF ground for VHF/UHF?

I believe quite a few would believe that on HF, but VHF/UHF. What do
you think would make a good RF ground for VHF/UHF?

A tub of mercury?

Nothing really.
I ground my antennas to a stake, but only for lightning protection.