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Old April 22nd 17, 05:25 PM posted to rec.radio.amateur.antenna
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Default Antenna for Marine VHF

In article , rickman
wrote:

Can you explain what would be preferable about the J-pole antenna? One
big disadvantage is that it appears to be more like 6 foot long for 2
meter use. That could be rather heavy and clumsy on a kayak.


Rick-

You are correct about the size. On the other hand, any separate antenna
for the VHF Marine band will be a bit clumsy on a kayak.

The "J" end of a J-pole is used to match a cable to the high impedance
of the end of a half wave element. One advantage of a vertical half
wave entenna is that it directs more energy towards the horizon,
compared to a quarter wave ground plane antenna.

Jeff Liebermann's analysis sounds like the best approach to VHF on a
kayak. But no matter which way you go, you are transmitting from a
point close to the water. You are limited to line-of-sight to another
kayak. Range to a base station will be mostly determined by the height
of the base station antenna.

Fred
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Old April 22nd 17, 05:43 PM posted to rec.radio.amateur.antenna
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Default Antenna for Marine VHF

On 4/22/2017 12:25 PM, Fred McKenzie wrote:
In article , rickman
wrote:

Can you explain what would be preferable about the J-pole antenna? One
big disadvantage is that it appears to be more like 6 foot long for 2
meter use. That could be rather heavy and clumsy on a kayak.


Rick-

You are correct about the size. On the other hand, any separate antenna
for the VHF Marine band will be a bit clumsy on a kayak.

The "J" end of a J-pole is used to match a cable to the high impedance
of the end of a half wave element. One advantage of a vertical half
wave entenna is that it directs more energy towards the horizon,
compared to a quarter wave ground plane antenna.

Jeff Liebermann's analysis sounds like the best approach to VHF on a
kayak. But no matter which way you go, you are transmitting from a
point close to the water. You are limited to line-of-sight to another
kayak. Range to a base station will be mostly determined by the height
of the base station antenna.


That is an issue I have already explored. There is not much hard
information available, but it would appear that the rubber ducky antenna
is adequate for use from one kayak to another for the most part. BTW,
that range is twice the distance to the horizon which is about two
nautical miles.

Communications to a land station such as the Coast Guard would be much
longer given the height of their antennas, unless your transmitted power
level is too low to reach them. You might be able to receive their
transmissions which are at a higher power, but they might not be able to
hear your transmissions. In that case a better antenna might make the
difference between rescue and not.

I've also considered the possibility of a higher powered unit built into
the boat with a small remote control. A cordless remote would be the
best option I believe and I expect they are available. A power boost
from 5W to 25W would easily beat the performance of a larger antenna.
Not sure how much this would weigh with a battery, but I don't think the
battery would need to be so large. It's not like 25W has to be used for
every transmission.

--

Rick C
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Old April 23rd 17, 12:38 AM posted to rec.radio.amateur.antenna
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Default Antenna for Marine VHF

On Sat, 22 Apr 2017, Fred McKenzie wrote:

In article , rickman
wrote:

Can you explain what would be preferable about the J-pole antenna? One
big disadvantage is that it appears to be more like 6 foot long for 2
meter use. That could be rather heavy and clumsy on a kayak.


Rick-

You are correct about the size. On the other hand, any separate antenna
for the VHF Marine band will be a bit clumsy on a kayak.

The "J" end of a J-pole is used to match a cable to the high impedance
of the end of a half wave element. One advantage of a vertical half
wave entenna is that it directs more energy towards the horizon,
compared to a quarter wave ground plane antenna.

Jeff Liebermann's analysis sounds like the best approach to VHF on a
kayak. But no matter which way you go, you are transmitting from a
point close to the water. You are limited to line-of-sight to another
kayak. Range to a base station will be mostly determined by the height
of the base station antenna.

And with a kayak, the issue is less about "antenna gain" than that there's
nothing with height on a kayak, and it's very low in the water.

Figure out some sort of "mast" and the problem is close to solved. Once
you have height, the actual antenna type matters less. I seem to recall
George Dyson put sails on some of his really big kayaks, so that's an
option, and the mast would provide some height for the antenna.

Michael

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Old April 23rd 17, 04:03 AM posted to rec.radio.amateur.antenna
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Default Antenna for Marine VHF

On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote:


... it would appear that the rubber ducky antenna
is adequate for use from one kayak to another for the most part. BTW,
that range is twice the distance to the horizon which is about two
nautical miles.


Conservative radio range on VHF is:
Nautical_Miles = 1.225 * sqrt(antenna_ht_feet)
Statute_Miles = 1.415 * sqrt(antenna_ht_feet)
km = 4.124 * sqrt(antenna_ht_feet)
Mo
http://www.qsl.net/kd4sai/distance.html

Communications to a land station such as the Coast Guard would be much
longer given the height of their antennas, unless your transmitted power
level is too low to reach them. You might be able to receive their
transmissions which are at a higher power, but they might not be able to
hear your transmissions. In that case a better antenna might make the
difference between rescue and not.


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.

I've also considered the possibility of a higher powered unit built into
the boat with a small remote control.


A higher power transmitter will help the Coast Guard hear you but will
do nothing for you hearing the Coast Guard. More antenna gain, and a
higher antenna are better solutions.

A cordless remote would be the
best option I believe and I expect they are available. A power boost
from 5W to 25W would easily beat the performance of a larger antenna.
Not sure how much this would weigh with a battery, but I don't think the
battery would need to be so large. It's not like 25W has to be used for
every transmission.


The biggest headache with using a 25 watt radio on battery power is
that the receive current drain is rather high thanks to the display
backlighting. For example:
http://www.standardhorizon.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=83&encPr odID=1BFCB309CEE0FEE9385740D0F23313FA&DivisionID=3 &isArchived=0
0.45A very low audio
0.8A full audio
5.0A 25 w transmit
1.0A 1 w transmit
So, let's say you start off with a 12V 7A-hr SLA battery commonly
found in a UPS. You don't want to kill the battery so let's only
drain it down to 40% capacity. That would give you:
12V * 7A-hr * 0.6 = 50.4 watt-hrs
In 25 watt transmit, that give you:
50.4 watt-hrs / (12v * 5A) = 0.84 hrs * 60 min/hr
= 50.4 minutes talk time
That's actually quite a long time for a fairly small battery.

However, if you leave it running in receive, you get:
50.4 watt-hrs / (12v * 0.45A) = 6.22 hrs listen time
That's at low audio. If you wanted to hear something or transmit, it
would be much lower.

You could do better with a LiIon battery pack. The problem is that
most such packs either 3 cells, which yields about 10.8V which is
insufficient, or 4 cells, which could be as high as:
4.1v * 4 = 16.4v
which might be over the maximum voltage rating for the radio. The
Standard GX1600 is rated for 11 to 16.5V operating voltage, so you
should be ok with 4 cells.

Yep, a 25 watt radio might work.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old April 23rd 17, 12:10 PM posted to rec.radio.amateur.antenna
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On Sat, 22 Apr 2017 20:03:49 -0700, Jeff Liebermann
wrote:


Conservative radio range on VHF is:
Nautical_Miles = 1.225 * sqrt(antenna_ht_feet)
Statute_Miles = 1.415 * sqrt(antenna_ht_feet)
km = 4.124 * sqrt(antenna_ht_feet)


Something is wrong with the km line above. Perhaps the antenna height
should be in meters? Or, the constant should be 2.278.


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Old April 23rd 17, 06:22 PM posted to rec.radio.amateur.antenna
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rickman wrote:
On 4/23/2017 10:17 AM, Ralph Mowery wrote:
In article ,
says...

On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote:


I've also considered the possibility of a higher powered unit built into
the boat with a small remote control.

A higher power transmitter will help the Coast Guard hear you but will
do nothing for you hearing the Coast Guard. More antenna gain, and a
higher antenna are better solutions.


Going from 5 to 25 watts of FM will gain almost nothing. Raising the
antenna several feet from the sitting down position will gain a lot.


Are you saying that a hand held 5 watt transceiver with a rubber ducky
antenna will reach all receivers because of the line of sight
limitation? Is that true even for contacting a land station with a 200
foot high antenna? A 3 foot high antenna and a 200 foot high antenna
give nearly 20 statute miles of range. Will 5 watts be heard that far
away?


Radio amateurs have launched satellites which usually have about 1 to 5 W
of power on VHF and UHF. Those can be clearly heard on a portable
with a very small antenna even when 2000-3000km away.

The loss of signal on line of sight is easy to overcome with narrow
band modulation and this kind of power. It is the "beyond line of sight"
attennuation that is the problem. Everything you can do to remove that
will help a lot more than power.

Today I was working at the repeater in our local radio/tv tower. We
were at 220m above ground level and it was easy to work over a repeater
about 80km away from us using only a handy with 1W of output. Only
because at that height this is (almost) line of sight.
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Old April 23rd 17, 06:27 PM posted to rec.radio.amateur.antenna
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In article , rickman
wrote:

A 3 foot high antenna and a 200 foot high antenna
give nearly 20 statute miles of range. Will 5 watts be heard that far
away?


Rick-

I have not done the calculations, but think your limit is line-of-sight
rather than power. I once talked 50 miles to an aircraft on Two Meters,
using a 1 watt handheld with rubber ducky antenna.

This assumes the Coast Guard does not have their squelch set too tight.

Fred
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