In article , rickman
wrote:

On 4/25/2017 12:07 PM, Fred McKenzie wrote:
In article , rickman
wrote:

On 4/24/2017 3:39 PM, Michael Black wrote:
On Sun, 23 Apr 2017, highlandham wrote:

On 23/04/17 04:03, Jeff Liebermann wrote:
quote =====
When you're on the water line, antenna height does make a big
difference. Prepare a roll of coax cable setup as an RF extension
cable. Attach connectors and adapters so that they fit the radio and
the antenna. If in trouble at sea, lash the antenna to the top of a
pole or oar to gain altitude. A separate antenna, such as a common
ground plane or coax sleeve antenna at the end of the coax cable would
make a better antenna than a rubber ducky.
unquote =====

A simple alternative to the J-Pole antenna would be a ground plane
antenna made of welding rod material on an SO-239 socket with a 4 hole
square flange with a vertical quarter wave radiator and 4 hinged
radial elements,the latter under 45 degrees when in use .
The SO-239 socket would be connected to a PL-259 connector and a
suitable length of coax.

But on a kayak? It won't do much good lying on the kayak, and unless
you get it high enough (which has problems in itself), you'll poke your
eye out.

Why not go for something that doesn't need horizontal radials.

Actually I gave this antenna some thought. If the radials were attached
by some sort of hinge for example a heavy braid, they could fold up
while still being electrically attached. The antenna could slide into a
tube when not in use. It might be a bit complex to rig up, but this is
the sort of thing I can give some thought to and maybe come up with
something workable.

Back to the J-Pole! You can make a light, flexible J-Pole out of 300
Ohm twinlead. Feed it with RG-174 cable. Use some kind of oar or pole
to raise it when needed.

I wouldn't know where to begin in sizing the components.

I did a quick search for 300 ohm j-pole. The first result was:
http://www.lowra.com/antenna/flexjpole/twinlead.pdf

Fred

In article , rickman wrote:

Yesterday I couldn't think of the term for the antenna style they use in
the commercial marine VHF antennas, but I believe it is called
"co-linear" or something like that. It is a bunch of coax sections
connected inner to outer at specific lengths. I have never seen a Ham
recommend using that type. But I guess Hams go more for permanent
installations with ground planes of some type. The co-linear needs no
ground plane I believe.

"Colinear" or "collinear", depending on whom you read. They're
basically a vertically-stacked array of individual radiating sections.

http://www.rason.org/Projects/collant/collant.htm

There are quite a few commercial ham antennas which use this approach
(the "Stationmaster" probably being the best known). They're fairly
popular for use on the 70 cm ham band, and some repeaters and base
stations use them on 2 meters.

This design is generally used when you want a substantial amount of
directional gain, and are willing to pay the price (length) for it.

I don't think this design would be a great choice for a kayak antenna,
because the individual coax sections in the "stack" are a
half-wavelength long (at the coax's velocity factor) and there are
usually quarter-wave sections at the top and bottom. The shortest
2-meter collinear (one half-wave section and two quarter-wave) would
be 2 meters in length - over six feet - and a marine VHF antenna
wouldn't be much shorter.

With a collinear of the type shown in the above link, you'd need to
mast-mount it up some distance - the bottom quarter-wave tube is
RF-hot, and if its bottom end is near water (or anything grounded) it
would tend to de-tune the antenna.

As others have noted, the OP really doesn't need a high-gain antenna.

On 4/25/2017 3:01 PM, Fred McKenzie wrote:
In article , rickman
wrote:

On 4/25/2017 12:07 PM, Fred McKenzie wrote:
In article , rickman
wrote:

On 4/24/2017 3:39 PM, Michael Black wrote:
On Sun, 23 Apr 2017, highlandham wrote:

On 23/04/17 04:03, Jeff Liebermann wrote:
quote =====
When you're on the water line, antenna height does make a big
difference. Prepare a roll of coax cable setup as an RF extension
cable. Attach connectors and adapters so that they fit the radio and
the antenna. If in trouble at sea, lash the antenna to the top of a
pole or oar to gain altitude. A separate antenna, such as a common
ground plane or coax sleeve antenna at the end of the coax cable would
make a better antenna than a rubber ducky.
unquote =====

A simple alternative to the J-Pole antenna would be a ground plane
antenna made of welding rod material on an SO-239 socket with a 4 hole
square flange with a vertical quarter wave radiator and 4 hinged
radial elements,the latter under 45 degrees when in use .
The SO-239 socket would be connected to a PL-259 connector and a
suitable length of coax.

But on a kayak? It won't do much good lying on the kayak, and unless
you get it high enough (which has problems in itself), you'll poke your
eye out.

Why not go for something that doesn't need horizontal radials.

Actually I gave this antenna some thought. If the radials were attached
by some sort of hinge for example a heavy braid, they could fold up
while still being electrically attached. The antenna could slide into a
tube when not in use. It might be a bit complex to rig up, but this is
the sort of thing I can give some thought to and maybe come up with
something workable.

Back to the J-Pole! You can make a light, flexible J-Pole out of 300
Ohm twinlead. Feed it with RG-174 cable. Use some kind of oar or pole
to raise it when needed.

I wouldn't know where to begin in sizing the components.

I did a quick search for 300 ohm j-pole. The first result was:
http://www.lowra.com/antenna/flexjpole/twinlead.pdf

Thanks.

--

Rick C

On 4/25/2017 3:19 PM, Dave Platt wrote:
In article , rickman wrote:

Yesterday I couldn't think of the term for the antenna style they use in
the commercial marine VHF antennas, but I believe it is called
"co-linear" or something like that. It is a bunch of coax sections
connected inner to outer at specific lengths. I have never seen a Ham
recommend using that type. But I guess Hams go more for permanent
installations with ground planes of some type. The co-linear needs no
ground plane I believe.

"Colinear" or "collinear", depending on whom you read. They're
basically a vertically-stacked array of individual radiating sections.

http://www.rason.org/Projects/collant/collant.htm

There are quite a few commercial ham antennas which use this approach
(the "Stationmaster" probably being the best known). They're fairly
popular for use on the 70 cm ham band, and some repeaters and base
stations use them on 2 meters.

This design is generally used when you want a substantial amount of
directional gain, and are willing to pay the price (length) for it.

I don't think this design would be a great choice for a kayak antenna,
because the individual coax sections in the "stack" are a
half-wavelength long (at the coax's velocity factor) and there are
usually quarter-wave sections at the top and bottom. The shortest
2-meter collinear (one half-wave section and two quarter-wave) would
be 2 meters in length - over six feet - and a marine VHF antenna
wouldn't be much shorter.

With a collinear of the type shown in the above link, you'd need to
mast-mount it up some distance - the bottom quarter-wave tube is
RF-hot, and if its bottom end is near water (or anything grounded) it
would tend to de-tune the antenna.

As others have noted, the OP really doesn't need a high-gain antenna.

I think the real problem is this antenna for 2 meter operation is 20
feet long! For marine VHF it can't be used on shore, so hanging it from
a tree would not work. When you say using a single half wave section
wouldn't be much different from a marine VHF antenna, what type of
antenna would a marine VHF antenna be? I thought they used a colinear
design.

--

Rick C

rickman wrote:
I don't think this design would be a great choice for a kayak antenna,
because the individual coax sections in the "stack" are a
half-wavelength long (at the coax's velocity factor) and there are
usually quarter-wave sections at the top and bottom. The shortest
2-meter collinear (one half-wave section and two quarter-wave) would
be 2 meters in length - over six feet - and a marine VHF antenna
wouldn't be much shorter.

With a collinear of the type shown in the above link, you'd need to
mast-mount it up some distance - the bottom quarter-wave tube is
RF-hot, and if its bottom end is near water (or anything grounded) it
would tend to de-tune the antenna.

As others have noted, the OP really doesn't need a high-gain antenna.

I think the real problem is this antenna for 2 meter operation is 20
feet long! For marine VHF it can't be used on shore, so hanging it from
a tree would not work. When you say using a single half wave section
wouldn't be much different from a marine VHF antenna, what type of
antenna would a marine VHF antenna be? I thought they used a colinear
design.

I wonder, why is the "2 meter band" not called the "6 1/2 feet band"
in the USA? This alternating between meters and feet is getting a
bit funny.

On 4/25/2017 4:24 PM, Rob wrote:
rickman wrote:
I don't think this design would be a great choice for a kayak antenna,
because the individual coax sections in the "stack" are a
half-wavelength long (at the coax's velocity factor) and there are
usually quarter-wave sections at the top and bottom. The shortest
2-meter collinear (one half-wave section and two quarter-wave) would
be 2 meters in length - over six feet - and a marine VHF antenna
wouldn't be much shorter.

With a collinear of the type shown in the above link, you'd need to
mast-mount it up some distance - the bottom quarter-wave tube is
RF-hot, and if its bottom end is near water (or anything grounded) it
would tend to de-tune the antenna.

As others have noted, the OP really doesn't need a high-gain antenna.

I think the real problem is this antenna for 2 meter operation is 20
feet long! For marine VHF it can't be used on shore, so hanging it from
a tree would not work. When you say using a single half wave section
wouldn't be much different from a marine VHF antenna, what type of
antenna would a marine VHF antenna be? I thought they used a colinear
design.

I wonder, why is the "2 meter band" not called the "6 1/2 feet band"
in the USA? This alternating between meters and feet is getting a
bit funny.

Why is the 70 cm band not the 700 mm band or the 0.07 meter band? Not
sure what issue you have with feet other than it not being familiar
perhaps. As much as I use metric, feet and inches are still ingrained
in my soul. When I look at a flag pole I don't think, geeze, that's 10
meters high! I think 30 feet. It's that simple.

--

Rick C

In article , rickman wrote:

I think the real problem is this antenna for 2 meter operation is 20
feet long!

Yup. Great for side-mounting on a tower, so-so for top-mounting on a
tower or mast (it'll sway in the breeze and this can wear out the
solder junctions), not so great for vehicle mounting, and downright
impractical for a hand-held :-)

For marine VHF it can't be used on shore, so hanging it from
a tree would not work. When you say using a single half wave section
wouldn't be much different from a marine VHF antenna, what type of
antenna would a marine VHF antenna be? I thought they used a colinear
design.

For "shortened" antennas, what you'll often find is that they're
"loaded" antennas. You can significantly shorten a radiating element,
and still have resonance, by adding an inductor of some sort - the
shortened element has capacitive reactance, and the inductor's
reactance (equal magnitude, opposite sign) cancels it out.

One way to do this is to wind the element itself into a spiral... this
adds inductance and lets you use a longer piece of wire
(i.e. something close to a quarter-wave).

Most "rubber duck" antennas are of this sort - they often have an
inductor in the base (right by the radio), and the whip consists of a
wire wound spiral-fashion around some sort of insulating core. If you
buy a hand-held marine-VHF radio, that's very likely what you'll get.

An example:

http://www.gandermountain.com/modper...ntenna&i=91538

Note they call it "Heliflex" - probably shorthand for "helically wound
flexible". It's only 1' long.

http://www.gandermountain.com/modper...ntenna&i=91513

This one is 6', or almost 2 meters. It might contain some sort of
center-fed dipole (fed up through the center of the lower element), or
it might be sort of the equivalent of a J-pole (half-wave or 5/8-wave
radiator with a matching stub or coil at the bottom).

In article ,
Rob wrote:

I wonder, why is the "2 meter band" not called the "6 1/2 feet band"
in the USA? This alternating between meters and feet is getting a
bit funny.

Fewer syllables? :-)

The ham bands have always been described in terms of meters, I
believe. Since amateur radio use is defined to a significant extent
by international treaty, and since the U.S. is very definitely in the
minority in terms of measurement units, it's just easier for all of
the hams to use the same (metric) terminology.

Also, wavelength and frequency convert back and forth a bit more
conveniently in metric, at least in terms of rough numbers (divide 300
by one, to get the other). Hence, "2-meter" is around 150 MHz.

On 4/25/2017 5:43 PM, Dave Platt wrote:
In article , rickman wrote:

I think the real problem is this antenna for 2 meter operation is 20
feet long!

Yup. Great for side-mounting on a tower, so-so for top-mounting on a
tower or mast (it'll sway in the breeze and this can wear out the
solder junctions), not so great for vehicle mounting, and downright
impractical for a hand-held :-)

For marine VHF it can't be used on shore, so hanging it from
a tree would not work. When you say using a single half wave section
wouldn't be much different from a marine VHF antenna, what type of
antenna would a marine VHF antenna be? I thought they used a colinear
design.

For "shortened" antennas, what you'll often find is that they're
"loaded" antennas. You can significantly shorten a radiating element,
and still have resonance, by adding an inductor of some sort - the
shortened element has capacitive reactance, and the inductor's
reactance (equal magnitude, opposite sign) cancels it out.

One way to do this is to wind the element itself into a spiral... this
adds inductance and lets you use a longer piece of wire
(i.e. something close to a quarter-wave).

Most "rubber duck" antennas are of this sort - they often have an
inductor in the base (right by the radio), and the whip consists of a
wire wound spiral-fashion around some sort of insulating core. If you
buy a hand-held marine-VHF radio, that's very likely what you'll get.

An example:

http://www.gandermountain.com/modper...ntenna&i=91538

Note they call it "Heliflex" - probably shorthand for "helically wound
flexible". It's only 1' long.

http://www.gandermountain.com/modper...ntenna&i=91513

This one is 6', or almost 2 meters. It might contain some sort of
center-fed dipole (fed up through the center of the lower element), or
it might be sort of the equivalent of a J-pole (half-wave or 5/8-wave
radiator with a matching stub or coil at the bottom).

Interesting. Any idea what the specs mean?

Gain 3dBi
"Marine Gain" 6dB

I know what dBi is, but what is Marine Gain? Is there some reference
antenna they use such as the rubber ducky?

--

Rick C

In article , rickman wrote:

Interesting. Any idea what the specs mean?

Gain 3dBi
"Marine Gain" 6dB

I know what dBi is, but what is Marine Gain? Is there some reference
antenna they use such as the rubber ducky?

That's probably taking into account an assumed 3 dB of additional
gain, due to the fact that the antenna is located a short distance
above the water surface. Salt water is an excellent reflector of RF
energy. At certain angles and distances, the primary wave from the
antenna and the reflected wave from the water surface will be in-phase
with one another, and will reinforce, doubling the strength of the
received signal.

In other places the two signals will largely or entirely cancel out.
There Ain't No Such Thing As A Free Lunch.