A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna.

http://www.amateurradio.bz/2m-70cm_v...e_antenna.html

I guess my first question is what would this be dual band? Is it
because it works over a range from 2 meters to 70 cm? Or is it somehow
tuned for both bands at the same time but not a lot in between?

This antenna would need to be vertically mounted, so would be a little
clumsy sticking three foot up from a kayak. Light weight would be
better than heavier. The construction plans call for stainless steel
material. Any reason to not use aluminum? Is diameter important? To
use aluminum I would want to use something thicker than 1/8 inch and
likely hollow. I believe TV antennas are usually made from 1/4 inch
tubing with maybe 1/16 inch thick walls. I guess that might make it
harder to bend without kinking. Would it be ok to make it with some
sort of couplers for the bends?

--

Rick C

On 4/21/2017 12:28 AM, rickman wrote:
A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna.

http://www.amateurradio.bz/2m-70cm_v...e_antenna.html

I guess my first question is what would this be dual band? Is it
because it works over a range from 2 meters to 70 cm? Or is it somehow
tuned for both bands at the same time but not a lot in between?

This antenna would need to be vertically mounted, so would be a little
clumsy sticking three foot up from a kayak. Light weight would be
better than heavier. The construction plans call for stainless steel
material. Any reason to not use aluminum? Is diameter important? To
use aluminum I would want to use something thicker than 1/8 inch and
likely hollow. I believe TV antennas are usually made from 1/4 inch
tubing with maybe 1/16 inch thick walls. I guess that might make it
harder to bend without kinking. Would it be ok to make it with some
sort of couplers for the bends?

I guess I should ask if the above antenna has much advantage over a
commercial VHF antenna about the same length like this one or maybe
longer. If the antenna can be lowered when not in use a *much* longer
antenna could be used as kayaks are quite long.

--

Rick C

rickman wrote:
A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna.

http://www.amateurradio.bz/2m-70cm_v...e_antenna.html

I guess my first question is what would this be dual band? Is it

This is an amateur radio antenna.
For marine VHF, get a marine VHF antenna. Duh.

On Fri, 21 Apr 2017 00:28:47 -0400, rickman wrote:

A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna.

http://www.amateurradio.bz/2m-70cm_v...e_antenna.html

No. The above antenna is tuned for 144 to 148MHz. Marine band
transmit is from 156.0 to 157.5Mhz transmit, and 161.975 to 162.6Mhz
for AIS and weather. You might be able to retune the Jpole antenna in
the above article, but my guess(tm) is that VWSR at the band edges is
too high. Another reason you don't see Jpole antennas in marine use
is that vertical radiation angle. Jpoles radiate most of their RF at
the horizon and above, not down. With fairly low gain, that's not a
problem with an antenna on the water line as the boat pitches and
rolls. It's a major problem with mast mounted antennas. It would be
better if the vertical radiation pattern was roughly symmetrical as in
this dual Jpole antenna. It would be interesting to see what a model
of this antenna looked like in 4NEC2.

I guess my first question is what would this be dual band? Is it
because it works over a range from 2 meters to 70 cm? Or is it somehow
tuned for both bands at the same time but not a lot in between?

Nope. It relys on the 3rd harmonic of 146Mhz being roughly on 440MHz.
There's usually a complex matching network on dual band antennas to
help keep the VSWR down, but this one apparently lacks even a balun.
For example, this is part of the guts of a Diamond X-50 dual band ham
antenna (after a friend backed his car into it breaking it in half).
http://802.11junk.com/jeffl/antennas/Misc/slides/x50-01.html

This antenna would need to be vertically mounted, so would be a little
clumsy sticking three foot up from a kayak. Light weight would be
better than heavier. The construction plans call for stainless steel
material. Any reason to not use aluminum?

Aluminum is fine. Anodizing might be a problem. Alodyne 1200 is
fine. Most paints are ok. Coat hangers suck. Watch out for
dissimilar metals in contact.

Is diameter important?

Larger outer diameter means wider bandwidth. You can use tubing in
order to get light weight.

To
use aluminum I would want to use something thicker than 1/8 inch and
likely hollow. I believe TV antennas are usually made from 1/4 inch
tubing with maybe 1/16 inch thick walls.

I'm too lazy to measure mine, but I would guess(tm) 0.5" diameter and
a very thin 0.031 wall diameter. TV needs all the bandwidth it can
get, so fat pipes are needed. The antenna also needs to be light and
cheap, so thin wall with seams is standard for TV.

I guess that might make it
harder to bend without kinking.

We used 6061-T6 for antennas. You can bend it in a tight turn if you
seal the ends and fill the tubing with sand:
http://www.wikihow.com/Bend-Aluminum-Pipe

Would it be ok to make it with some
sort of couplers for the bends?

Sure. The bend does not need to be contiguous. A bar with two holes
drilled in it for the two elements should work (and be adjustable).

Suggestion: Look at various commercial VHF antennas and build
something similar. You'll be amazed at how crude they are inside. One
common antenna (I forgot the maker and model) used a fiberglass radome
with a length of 1/4" wide copper tape stuck to the inside of the tube
for driven elements.

--
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 Fri, 21 Apr 2017 18:28:32 +0100, Jeff wrote:

No. The above antenna is tuned for 144 to 148MHz. Marine band
transmit is from 156.0 to 157.5Mhz transmit, and 161.975 to 162.6Mhz
for AIS and weather. You might be able to retune the Jpole antenna in
the above article, but my guess(tm) is that VWSR at the band edges is
too high.

I think you are misinterpreting what this antenna is. It is not a J-pole.
It is basically 2 closely coupled dipoles one on 2m and the other on 70cms.
The drawing that looks like a j-pole is one half of the antenna ie an
element cut to 2m and the other 70cms.
Jeff

Oops. Y'er right. It's not a Jpole, although it looks like one. More
like a "fan dipole":
https://www.google.com/search?q=fan+dipole&tbm=isch
The 18.63" is 1/4 wave at 2m and 6.25" is 1/4 wave at 440Mhz. Thanks.

Incidentally, I forgot to mumble that one doesn't need two dipoles to
operate on just the marine band. Also, I can get similar performance
out of an 18" bow tie dipole antenna (and balun), or a biconical
porcupine:
http://802.11junk.com/jeffl/antennas/biconical/index.html

--
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 , rickman
wrote:

A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna.

http://www.amateurradio.bz/2m-70cm_v...e_antenna.html

I guess my first question is what would this be dual band? Is it
because it works over a range from 2 meters to 70 cm? Or is it somehow
tuned for both bands at the same time but not a lot in between?

This antenna would need to be vertically mounted, so would be a little
clumsy sticking three foot up from a kayak. Light weight would be
better than heavier. The construction plans call for stainless steel
material. Any reason to not use aluminum? Is diameter important? To
use aluminum I would want to use something thicker than 1/8 inch and
likely hollow. I believe TV antennas are usually made from 1/4 inch
tubing with maybe 1/16 inch thick walls. I guess that might make it
harder to bend without kinking. Would it be ok to make it with some
sort of couplers for the bends?

Rick-

I did not watch the video. I believe the antenna is "dual band" because
it happens to also work on a frequency band that is three times the
basic frequency. In other words, 146 and 440. That does not appear to
make any difference with regard to the Marine VHF band. You would
simply scale the dimensions by the ratio of the Two Meter frequency to
the Marine band frequency, 146/156.

That said, the antenna in the article does not appear to be the best
choice for your application. The "J-Pole" antenna Jeff suggested would
be my choice. Do some research on the J-Pole, but remember to design it
for 156 instead of 146 MHz.

Fred
K4DII

On 4/21/2017 1:51 PM, Fred McKenzie wrote:
In article , rickman
wrote:

A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna.

http://www.amateurradio.bz/2m-70cm_v...e_antenna.html

I guess my first question is what would this be dual band? Is it
because it works over a range from 2 meters to 70 cm? Or is it somehow
tuned for both bands at the same time but not a lot in between?

This antenna would need to be vertically mounted, so would be a little
clumsy sticking three foot up from a kayak. Light weight would be
better than heavier. The construction plans call for stainless steel
material. Any reason to not use aluminum? Is diameter important? To
use aluminum I would want to use something thicker than 1/8 inch and
likely hollow. I believe TV antennas are usually made from 1/4 inch
tubing with maybe 1/16 inch thick walls. I guess that might make it
harder to bend without kinking. Would it be ok to make it with some
sort of couplers for the bends?

Rick-

I did not watch the video. I believe the antenna is "dual band" because
it happens to also work on a frequency band that is three times the
basic frequency. In other words, 146 and 440. That does not appear to
make any difference with regard to the Marine VHF band. You would
simply scale the dimensions by the ratio of the Two Meter frequency to
the Marine band frequency, 146/156.

The link is not a video. I appreciate the speculation, but I am
researching this and am looking for facts. As others have pointed out,
the design is basically a dipole but with J shaped elements 47.3 and
15.9 cm lengths. Someone else has suggested this is essentially a pair
of dipoles of the two lengths.

Usually a theoretical analysis can be found for any given antenna
design, but I have not found anything other than construction projects
for this design. They don't seem to cover theoretical aspects.

That said, the antenna in the article does not appear to be the best
choice for your application. The "J-Pole" antenna Jeff suggested would
be my choice. Do some research on the J-Pole, but remember to design it
for 156 instead of 146 MHz.

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 C

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

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

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