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sk
 
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Default Antenna Ratings

Know anywhere I can find ratings to help decide which antenna?? I have a 23
foot center console. Generally range 10-15 miles offshore and plan to mount
the antenna on my


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Larry W4CSC
 
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Default Antenna Ratings

On Mon, 29 Dec 2003 03:00:38 GMT, "sk" wrote:

Know anywhere I can find ratings to help decide which antenna?? I have a 23
foot center console. Generally range 10-15 miles offshore and plan to mount
the antenna on my


I don't recommend the very high gain fiberglass antennas for VHF on
small boats that roll so much in swell.

High gain antennas get their high gain from squeezing the vertical
antenna's donut-shaped radiation pattern into one that looks like you
stepped on the donut. As long as the antenna is vertical, this is
fine and steps up the gain very nicely. But, as the antenna is TILTED
in any direction, this flattened-out pattern also tilts,
simultaneously, radiating all that power into the sea on one side and
into the clouds on the other, putting the receiving station in an area
of its radiation pattern that is more of a null, than it would be if
you had used a simpler 1/2 wave vertical whip with the fat donut
pattern. The effect on the signal at the receiver when the super
antenna is rolling around is a signal that's fading in and out as the
high gain pattern plays over the receiving station on its way to
skyward or seaward as the boat rolls.

The best small boat antenna is an end-fed, half wave as high up as you
can mount it. I've used Metz antennas since they started making
home-brew ham antennas in the 70's. Metz antennas have a no-nonsense
LIFETIME warranty! Who could ask for more?
http://www.metzcommunication.com/
I think the Manta 6 is the finest small boat antenna made.
http://www.metzcommunication.com/manta6.htm
It is a simple 1/2 wave, no ground plane, end-fed VHF antenna and will
work anywhere you can put it, plastic, metal, ground or not. The
connector on the bottom of it is the standard SO-239 "CB" connector.
If you break the coil, they'll send you a new one. The whip is fine
stainless steel and the only way you can break it is by FORCE. I have
LOST a couple of them overboard over the years when the little clamp
on top of the coil wasn't tight, though.....

Shakespeare also makes an end-fed halfwave, but it sucks because the
COAX IS PERMANENTLY MOUNTED IN IT so you can't FIX IT when it breaks!
You also can't simply replace a lost whip with a piece of coat hangar
wire, like you can on the Metz, out in the boondocks to get the radio
working again......

Metz has lots of different crazy mounts for it.....


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Chuck Tribolet
 
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Default Antenna Ratings

Larry: please define "very high gain"? 9db? 6db?

FWiW, I have have a 6db 8' Shake Galaxy on my 17' whaler. Works fine
even when it's rock and roll.

--
Chuck Tribolet

http://www.almaden.ibm.com/cs/people/triblet

Silicon Valley: STILL the best day job in the world.


"Larry W4CSC" wrote in message ...
On Mon, 29 Dec 2003 03:00:38 GMT, "sk" wrote:

Know anywhere I can find ratings to help decide which antenna?? I have a 23
foot center console. Generally range 10-15 miles offshore and plan to mount
the antenna on my


I don't recommend the very high gain fiberglass antennas for VHF on
small boats that roll so much in swell.

High gain antennas get their high gain from squeezing the vertical
antenna's donut-shaped radiation pattern into one that looks like you
stepped on the donut. As long as the antenna is vertical, this is
fine and steps up the gain very nicely. But, as the antenna is TILTED
in any direction, this flattened-out pattern also tilts,
simultaneously, radiating all that power into the sea on one side and
into the clouds on the other, putting the receiving station in an area
of its radiation pattern that is more of a null, than it would be if
you had used a simpler 1/2 wave vertical whip with the fat donut
pattern. The effect on the signal at the receiver when the super
antenna is rolling around is a signal that's fading in and out as the
high gain pattern plays over the receiving station on its way to
skyward or seaward as the boat rolls.

The best small boat antenna is an end-fed, half wave as high up as you
can mount it. I've used Metz antennas since they started making
home-brew ham antennas in the 70's. Metz antennas have a no-nonsense
LIFETIME warranty! Who could ask for more?
http://www.metzcommunication.com/
I think the Manta 6 is the finest small boat antenna made.
http://www.metzcommunication.com/manta6.htm
It is a simple 1/2 wave, no ground plane, end-fed VHF antenna and will
work anywhere you can put it, plastic, metal, ground or not. The
connector on the bottom of it is the standard SO-239 "CB" connector.
If you break the coil, they'll send you a new one. The whip is fine
stainless steel and the only way you can break it is by FORCE. I have
LOST a couple of them overboard over the years when the little clamp
on top of the coil wasn't tight, though.....

Shakespeare also makes an end-fed halfwave, but it sucks because the
COAX IS PERMANENTLY MOUNTED IN IT so you can't FIX IT when it breaks!
You also can't simply replace a lost whip with a piece of coat hangar
wire, like you can on the Metz, out in the boondocks to get the radio
working again......

Metz has lots of different crazy mounts for it.....




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Harry Krause
 
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Default Antenna Ratings

Chuck Tribolet wrote:

Larry: please define "very high gain"? 9db? 6db?

FWiW, I have have a 6db 8' Shake Galaxy on my 17' whaler. Works fine
even when it's rock and roll.


I have an 8' "Digital" brand antenna hooked up to my VHF on my 25'
Parker pilothouse. Works fine in the rock and roll of the Atlantic Ocean.

Visit the boat at:

http://photos.yahoo.com/hakrause



--
Email sent to is never read.
  #5   Report Post  
Larry W4CSC
 
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Default Antenna Ratings

On Sun, 28 Dec 2003 21:49:17 -0800, "Chuck Tribolet"
wrote:

Larry: please define "very high gain"? 9db? 6db?


The higher the "gain" of the antenna, the flatter and less "thick" its
radiation pattern. The 9db antenna has a much flatter radiation
pattern than the 6db.

FWiW, I have have a 6db 8' Shake Galaxy on my 17' whaler. Works fine
even when it's rock and roll.

"In range" you'll really not see the difference on FM, which signal
strength has less effect on until it's near the fringe.

I just don't like the big, long fiberglass whips on small boats.
Neither does USCG. They got fed up with them breaking off and all use
the Metz, now. Metz brags about it on their webpage.

If jumping waves with the SeaRayder jetboat can't break it, your boat
won't, either. Mine is even mounted way up in the bow and has
survived even submarining the bow at speed.....drowning us all in the
process...(c;

A fiberglass tube filled with hookup wire antenna elements would never
make it....hee hee.




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Larry W4CSC
 
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Default Antenna Ratings

On Wed, 31 Dec 2003 11:30:07 GMT, Jack Burton
wrote:

On Tue, 30 Dec 2003 04:01:15 GMT, (Larry W4CSC) wrote:

On Sun, 28 Dec 2003 21:49:17 -0800, "Chuck Tribolet"
wrote:

Larry: please define "very high gain"? 9db? 6db?


The higher the "gain" of the antenna, the flatter and less "thick" its
radiation pattern. The 9db antenna has a much flatter radiation
pattern than the 6db.


So, how does the horizon work into the gain equation?


Picture the vertical antenna standing vertically. It's a high-gain
fiberglass type with many phased elements imbedded into it. Its
radiation pattern is perpendicular to the antenna in a flattened donut
shape. When you step on a donut, its outer edge moves outward as its
thickness is squeezed. That's exactly what's happening to get more
radiation to the horizon where the receiving station is located. The
phased array squeezes the fat round donut of the 1/2 wave, which
bulges out in the middle making a bigger signal perpendicular to the
antenna. This pattern moves with the antenna, always perpendicular to
it.

Now, tilt the antenna towards the receiving station. (Boat pitched?)
The flattened donut is now pointing into the water on the side towards
the receiving station. The signal level at the receiving station
drops, drastically, because this pattern is so flattened. On an FM
receiver, you hear no difference in signal "loudness" as signal
varies, UNTIL that signal drops below the receiver's noise floor,
usually a few hundredths of a microvolt, at which point the receiver
"hiss" of its FM detector gets louder and louder. As the signal
increases, again, the FM receiver "quiets", the hissing drops. This
is the only time the effect of the high gain antenna's flattened
pattern will cause communications problems. If the antenna's received
signal drops from 800 uV to 40 uV, you won't notice it. 40 uV will
keep the receiver hiss quiet. But, if we are talking about adding
this pattern tilting effect to the boat riding down into the trough of
those 30' rollers in a "worst case scenario" where it really counts,
THEN we are talking about disrupted comms. The best antenna for this
situation is NOT the 9dB fiberglass beast mounted on the side of the
helm console.....but the 1/2 wave Metz stainless whip mounted as high
up as you can get it.....with its fat pattern less effected by tilting
that's still sticking up above the waves on top of the sailboat
mast....like a beacon from the lighthouse.


FWiW, I have have a 6db 8' Shake Galaxy on my 17' whaler. Works fine
even when it's rock and roll.

"In range" you'll really not see the difference on FM, which signal
strength has less effect on until it's near the fringe.

I just don't like the big, long fiberglass whips on small boats.
Neither does USCG. They got fed up with them breaking off and all use
the Metz, now. Metz brags about it on their webpage.


Interesting - all the USCG small boats around these parts use the
Shakespeare 396-1 which is a center-fed 1/2 wave.

I use one and it's been great antenna.

That's the best antenna mounted as high as you can get it. It's
end-fed by a transformer in that cylinder base. It requires no
groundplane. I just don't like the way I can't replace the broken
cable permanently mounted to it up inside.....or the screwed-on whip
because I can't slip a 34" piece of coat hanger into the end when the
whip gets busted off by that little pitchpole we did sideways to that
Perfect Strom roller in the night. The Metz whip is mounted in a
gripping ferrule. Coat hanger wire slips right in where the broken
whip comes out.


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Shortwave Sportfishing
 
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On Thu, 01 Jan 2004 16:11:49 GMT, (Larry W4CSC) wrote:

On Wed, 31 Dec 2003 11:30:07 GMT, Jack Burton
wrote:


~~ major snippage ~~

But, if we are talking about adding
this pattern tilting effect to the boat riding down into the trough of
those 30' rollers in a "worst case scenario" where it really counts,
THEN we are talking about disrupted comms. The best antenna for this
situation is NOT the 9dB fiberglass beast mounted on the side of the
helm console.....but the 1/2 wave Metz stainless whip mounted as high
up as you can get it.....with its fat pattern less effected by tilting
that's still sticking up above the waves on top of the sailboat
mast....like a beacon from the lighthouse.


Yes, that is true enough on a sail boat because you are talking about
height in that case which can conquer a multitude of conditions nine
foot antenna or three foot base loaded (end fed) stainless steel.

I'm speaking about a small boat as in, oh say, a 23 foot CC Ranger
with a T-top or a 32 foot Contender with a T-top. I would think that
even in your scenario, the angle of the signal to the horizon when it
leaves the antenna would work the same base load or center fed and
cause signal capture problems at the receiving end regardless.

By the way, neither of those boats would ever be in a situation with
30 foot rollers - if they show up, I'm long gone. :)

FWiW, I have have a 6db 8' Shake Galaxy on my 17' whaler. Works fine
even when it's rock and roll.

"In range" you'll really not see the difference on FM, which signal
strength has less effect on until it's near the fringe.

I just don't like the big, long fiberglass whips on small boats.
Neither does USCG. They got fed up with them breaking off and all use
the Metz, now. Metz brags about it on their webpage.


Interesting - all the USCG small boats around these parts use the
Shakespeare 396-1 which is a center-fed 1/2 wave.

I use one and it's been great antenna.

That's the best antenna mounted as high as you can get it. It's
end-fed by a transformer in that cylinder base. It requires no
groundplane.


How can an antenna work without a ground plane? At the frequencies
we're discussing, the ground effect in FM is about the same as it is
in AM if I understood your discussion points (deleted from this post)
correctly.

I just don't like the way I can't replace the broken
cable permanently mounted to it up inside.....or the screwed-on whip
because I can't slip a 34" piece of coat hanger into the end when the
whip gets busted off by that little pitchpole we did sideways to that
Perfect Strom roller in the night. The Metz whip is mounted in a
gripping ferrule. Coat hanger wire slips right in where the broken
whip comes out.


Wellm to each their own I guess. :)

Later,

Tom
S. Woodstock, CT
----------
"I object to fishing tournaments less for
what they do to fish than what they do to
fishermen." Ted Williams - 1964
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Larry W4CSC
 
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On Thu, 01 Jan 2004 18:06:55 GMT, Shortwave Sportfishing
wrote:


How can an antenna work without a ground plane? At the frequencies
we're discussing, the ground effect in FM is about the same as it is
in AM if I understood your discussion points (deleted from this post)
correctly.


Modulation has no effect on antenna physics. The object is to fit at
least 1/2 wavelength onto a conductor. Where it is fed is of no
consequence to radiation, but does effect the feedpoint impedance.

As to the "ground plane".....

In an HF antenna, we are always dealing with an antenna where the
practical length is far shorter than the ideal length. At 7 Mhz, a
1/2 wave antenna is about 65' long. Any 1/2 wave dipole antenna is
complete and there is no ground plane. A ground plane is only
required if your antenna design includes an image antenna. Case in
point:

Look at 90% of the AM broadcast antennas in your area. Some AM
stations actually DO have 1/2 wavelength antennas, but a 1000 Khz this
is 468' long and is expensive to erect and keep erected, so they only
do it when they have no other choice. A 1/2 wavelength AM tower
requires no extensive ground radial system, either, so it would be
located in a dense city where you cannot lay out long radials to bury.
Most AM transmit antennas are near 1/4 wavelength in length (a 108" CB
stainless whip on Bubba's pickup is a 1/4 wavelength antenna on 27
Mhz). To get this 1/4 wavelength to "tune" (resonate), we have to
bend the other half wavelength and lay it out sideways in an L
pattern. However, erecting just an L 1/2 wave antenna fed at the
corner of the L creates a radiation pattern in the direction of the
horizontal of the L. To counter this effect, more horizontal elements
are laid out around the base of the 1/4 wave vertical part to make the
pattern omnidirectional, like the 1/2 wave resonant antenna. The end
result is like a CB "ground plane" antenna for 27 Mhz. A 1/4 wave
vertical over a set of "ground plane" radials, which don't have to be
buried to work.

On VHF marine at 160 Mhz, a whole half-wave antenna needs only be 34"
long, so there is no need to resort to shortened whips working against
"ground plane". The Metz antenna is a 34" stainless whip with an
autotransformer on the end of it that raises the feedpoint from 52
ohms, the cable impedance to the transmitter, up to several hundred
ohms, which excites the already-resonant element. No ground of any
kind is required, or desired.

Like you say, to each his own.

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Shortwave Sportfishing
 
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On Fri, 02 Jan 2004 05:12:36 GMT, (Larry W4CSC) wrote:

On Thu, 01 Jan 2004 18:06:55 GMT, Shortwave Sportfishing
wrote:


How can an antenna work without a ground plane? At the frequencies
we're discussing, the ground effect in FM is about the same as it is
in AM if I understood your discussion points (deleted from this post)
correctly.


Modulation has no effect on antenna physics. The object is to fit at
least 1/2 wavelength onto a conductor. Where it is fed is of no
consequence to radiation, but does effect the feedpoint impedance.

As to the "ground plane".....


~~ snippage ~~

Well, you kind of danced around the answer, but I'd still like to know
how the ground plane effects the radiation angle which logically would
also have an effect on reception of a signal. On page 3-9 of the ARRL
Antenna Handbook (16th addition - sorry, it's the latest I have at
hand at the moment) states:

"The total current in the antenna consists of two components. The
amplitude of the first is determined by the power supplied by the
transmitter and the free-space radiation resistance of the antenna.
The second component is induced in the antenna by the wave reflected
by the ground. This second component, while considerably smaller than
the first at most usefull antenna heights, is by no means
insignificant."

So it would seem that the "ground plane/wave" is not an umimportant
consideration when considering antennas.

Further on that same page, is the following:

"Changing the height of the antenna above the ground will change the
current flow assuming that the power to the antenna is constant."

Again, it would appear that the "ground plane/wave" is not
insignificant.

Now, as I understand it, at VHF frequencies, the methodology of
providing energy to the antenna (loading/feed) is not as important to
the generation/reception of the signal as is height. In fact, if I
read the pattern charts correctly, the height of the antenna has more
to do with the lobe pattern (the donut you were discussing) than the
method of feeding the antenna.

Yes/No?

Later,

Tom
S. Woodstock, CT
----------
"I object to fishing tournaments less for
what they do to fish than what they do to
fishermen." Ted Williams - 1964
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