I've seen quite a few rigged this way. Must be worth something.

Doug
s/v Callista

"David Swindon" wrote in message
...

"Bruce in Alaska" wrote in message
...

So your preformance below 4 Mhz will be drastically
reduced with antennas of less than 50 ft of electrical length.
If your using MF Frequencies for comms of less than 400 miles,
which is what they are there for, you will need a longer
antenna.

Bruce in alaska
--
add a 2 before @

Theres been some really good discussion here. In my experiance cruising we
used a whole range of frequencies as sometimes we were communicating with
boats in the same area, and other times with boats back in home port. With
regard to the need for a longer antenna for short range (definatly
required)
what are your thoughts on tying the triatic into the backstay as part of
the
antenna system (the triatic is 14' long - although as the mizzen is
shorter
than the main mast, the angle between the triatic and backstay is only
about
30 degrees).

A 50' or 75' whip would be a bit ungainly

Doug
s/v CAllista

"Bruce Gordon" wrote in message
...
In article ,
Gary Schafer wrote:

As Bruce says, "tuners get very lossy with short antennas". But that
is not the only problem with short antennas. The antenna and ground
system become very lossy with short antennas. Below 1/4 wavelength the
radiation resistance of the antenna drops drastically. It can be less
than an ohm. That equates to very high losses. The antenna system in
those cases may be only a few percent efficient.

It is far better to have a longer antenna that gives a much higher
radiation resistance even if it may not be the optimum length as far
as radiation pattern is concerned. If you can't get the power to the
antenna the radiation pattern doesn't much matter. You still won't get
out very well.

On a typical boat the radiation pattern is going to be far from ideal
with whatever length antenna you have due to all the surrounding
objects on the boat.

The difference in radiation patterns between a 1/2 wavelength and 5/8
wavelength antennas are minimal. About the only real difference is the
feed point impedance they present.

As far as antennas greater in length than a quarter wavelength, they
start to produce multiple lobes in the pattern. Which on a boat may
not be a bad thing. As you mention, sometimes higher angles are
desired depending on the distance trying to be covered.

A longer antenna on a typical boat is most always going to be more
efficient than a short antenna even if the longer antenna produces
multiple pattern lobes.

Regards
Gary

Exactly, Doug says he does fairly well on 80 and 40 Meters with
a 23' whip and an autotuner. We take him at his word, but if he
would figure out how to increase that to 50' or 75', there is a GOOD
chance that he would do better, and even in poorer band conditions.
It doesn't take much power or antenna to communicate if the band is
open, to where you want to talk, on the frequency that your using.
Try that if the bands isn't so hot and the time of day is against
you, with a Very Marginal antenna system. Yea, I know most pleasure
boaters have never heard of Marine Frequencies below 4Mhz, but up
here in Alaska we have been using 1.6Mhz and 2.0Mhz - 4Mhz Marine
frequencies for years, and very suscessfully, even on Poor Band Years.
I have used 3261Khz for Maritime Comms for 35 years, and worked my
Fleet Vessels, with 65% completion of Comms, rate on a daily basis.
You will not get that kind of connectitvity, with a 23' antenna,
on your Maritime Mobile Stations. In the "Good Old Days", the previous
generation of Alaskan RadioMen used to work 1630Khz consistantly
every night for intercompany Comms.

Just because SGC says their tuner only needs 23ft of wire, doesn't mean
that you can actually talk to anyone with that type of system. By the
way SGC didn't do the design of that autotuner, themselves, they stole
it from SEA, and didn't even change the "CopyWrite Statement" in the
firmware code. All autotuners on the market today, come from the
original design work of Bill Schillb, an engineer for Motorola MF/HF
Systems, at the time. He worked out the basics of the tuning code and
the hardware design. When he left Motorola and came out west to
Seattle, he landed at Northern Radio for s short while, and while there
passed on the basic technology to Bill Forgey, who was Chief Engineer at
Nothern at the time. Both Bill's left Northern Radio just before it
went under, with Forgey taking the whole Design Team with him, and with
Dick Stephens started SEA. (Stephens Engineering Asscoiates) Dick was
the Chief Engineer at Northern before Bill, and his mentor. Bill Forgey
along with Mark Johnson (an ex Northern Tech) designed the first truely
Marine Radio Autotuner which was the SEA1600, using the basics that Bill
Schillb had imparted, and on which, they improved and expanded. The
first autotuner that had Frequency Memory and Instant Band Switching was
the SEA1612, and the B version is what SGC copied for their 23x series
tuners. Icom, Kenwood, Furuno, and the rest are "Johnnie Come Latelys"
in the world of Marine Autotuner design, and basically they reverse
engineered the SEA design and firmware, for their systems.

I was closely associated with these folks as a Traveling Radio Tech for
Northern Radio, before leaving to become Comm Supt. for the largest
Salmon Canner in Alaska. I count all these folks a close friends, even
after all these years, and also while working the Dark Side (I was a
Field Agent for the FCC for five years) of the industry. I also did a
pile of beta testing over the years for SEA, that included most of their
designs for autotuners. Some of the prototypes are still in use today,
in various places in alaska. I designed and installed the first Marine
Autotuner feeding a Dipole Antenna, and that system is still in use
today. Bill, Mark and I designed and built a 1Kw Maritime Mobile Coast
Station that has 8 Control Points, and uses a SEA1612B Autotuner, and
one of a kind Dipole Antenna for MF/HF Frequencies from 1630Khz
thru 30Mhz at the 150W PEP level, and 1Kw on 4Mhz, 6Mhz, 8Mhz, 12Mhz
16Mhz, 22Mhz Marine Frequencies, using another special Dipole Antenna,
from Morad Electronics. This system is still in use today as well, and
has been around for more than 10 years.

I don't usually "Toot my own horn", but I do have considerable practical
experience in this field, as well as a long history in the industry.



Bruce in alaska onetime Fed, and long time Radioman..........

--
Bruce (semiretired powderman & exFCC Field Inspector for Southeastern
Alaska)
add a 2 before @
Bruce Gordon * Debora Gordon R.N. Bruce's Trading Post
P.O. Box EXI Excursion Inlet South
Juneau, Alaska 99850 Excursion Inlet, Alaska 99850
www.btpost.net www.99850.net

Hello Gary:

Seems I've simply lost the ability to communicate any more. My point was
that seeking the most efficient antenna (as defined by maximum power
transfer into space) ought not to be the guiding principle. We want
maximum power delivered to the other station. All other things the same,
a higher radiation resistance would mean lower ohmic losses. But all
other things are not the same when antenna length is increased.

Yes, radiation patterns on real boats will differ from radiation
patterns in space. But even on a real boat, a high percentage of energy
is radiated at quite high angles when the antenna is a half-wavelength.
Yes, the half-wave will be more "efficient" in getting energy off the
boat because the radiation resistance is higher than with a shorter
antenna. But if it doesn't get the signal to the other station because
the radiation angle is too high, then it's not really optimal. Look at
some numbers on vertical radiation patterns. You can easily lose 6 db at
useful, low radiation angles by going from a quarter-wave to a
hslf-wave. There is no way you'll ever recover that through the
half-wave's higher radiation resistance, although that high-angle stuff
could actually be a good thing if you're not in the middle of the
Pacific trying to work Europe. And we have not even addressed the
consequences of a sloping antenna on both horizontal and vertical patterns.

No quarrel, of course, with your observation that as the length of an
antenna falls below a quarter-wave, the radiation resistance (and thus
radiated efficiency) falls. Those losses are one of the parameters that
one needs to weigh against other considerations. At the same time, a
reduction of length to say, .2 wavelengths would probably not even be
detectable (i.e., 1 dB). Also, even as the length decreases, the
radiation pattern remains basically that of a quarter-wave antenna.

I probably need to repeat that I have not advocated "shorter" antennas,
"longer" antennas, quarter-wave antennas, half-wave antennas, vertical
antennas, horizontal antennas or much of anthing other than an analysis
of the desired signal paths and the basing of an antenna design and
frequency combination on that analysis. Well, I have also cautioned
against blindly increasing antenna length. Sort of struck me as a
motherhood kind of thing.

Onward . . .

Chuck



Gary Schafer wrote:
As Bruce says, "tuners get very lossy with short antennas". But that
is not the only problem with short antennas. The antenna and ground
system become very lossy with short antennas. Below 1/4 wavelength the
radiation resistance of the antenna drops drastically. It can be less
than an ohm. That equates to very high losses. The antenna system in
those cases may be only a few percent efficient.

It is far better to have a longer antenna that gives a much higher
radiation resistance even if it may not be the optimum length as far
as radiation pattern is concerned. If you can't get the power to the
antenna the radiation pattern doesn't much matter. You still won't get
out very well.

On a typical boat the radiation pattern is going to be far from ideal
with whatever length antenna you have due to all the surrounding
objects on the boat.

The difference in radiation patterns between a 1/2 wavelength and 5/8
wavelength antennas are minimal. About the only real difference is the
feed point impedance they present.

As far as antennas greater in length than a quarter wavelength, they
start to produce multiple lobes in the pattern. Which on a boat may
not be a bad thing. As you mention, sometimes higher angles are
desired depending on the distance trying to be covered.

A longer antenna on a typical boat is most always going to be more
efficient than a short antenna even if the longer antenna produces
multiple pattern lobes.

Regards
Gary



On Tue, 09 Nov 2004 00:29:53 GMT, Chuck wrote:


Antennas are really a lot like boats: No
boat will do everything well and no
antenna will either. Boats and antennas
that try to do everything usually fail
across the board.

FWIW, SGC-237, -230, and -231 tuners
need 23 feet only to tune from 1.6 MHz
to 3.3 MHz. Above 3.3 MHz, these SGC
tuners require only eight (8) feet.

The Icom AH-4, for example, needs 23
feet only to tune down to 3.5 MHz, but
will tune from 7 MHz up with Icom's
AH-2b whip (8.2 feet long).

But it doesn't matter what lengths the
tuners require if there is no desire to
operate in that frequency range, and
chances are excellent that recreational
boaters will not be found at the very
low frequencies.

As has been pointed out, some antenna
lengths will be more taxing for an
autotuner than other lengths. Your
objective is not to make life easier for
your tuner, especially when doing so may
move you farther from your real needs.
You may not even need a tuner! Your
objective is to achieve your
communication goals.

You might give some thought to posting
on one of the cruising newsgroups to ask
experienced cruisers for their thoughts
on things like "if you had only one
frequency to operate on, what would it
be? Among other things, that might be
the basis for an antenna you can stow
for emergencies. But tell them where and
how you'll be cruising and what you want
the ssb for (email, emergencies,
boat-to-boat communication, etc.) Then
return to the antenna design questions.

Keep to it!

Chuck

Well do I have egg on my face!

Gary, you are correct, of course, in stating that there is not a lot of
difference between the vertical radiation patterns of half-wave and
quarter-wave antennas. Surely not the differences I was alluding to.

And so my statements to the contrary were just plain wrong.

While I was writing half-wave, I was thinking of something longer, like
3/4 wave. I should have been more careful and I do apologize.

My point, however, is just as valid. Many sailboats sport 45' backstay
antennas and that is close to 3/4 wavelength in the 15 MHz range. A 3/4
wave antenna has maximum vertical radiation at 45 degrees! I would say a
16- or even an 8-foot whip would be very competitive with such a
backstay antenna at the lower radiation angles needed for transoceanic
communication.

At higher marine frequencies, 3/4 wavelength is obviously even less than
45 feet.

Of course, the 3/4 wave will be efficient and easy on the autotuner.

I'll try to keep my brain in synch with my typing, henceforth.

Chuck

"Bruce in Alaska" wrote in message
...



Is that the rigging that goes between the mizzenmast and the mainmast
near their tops?

Bruce in alaska
--
add a 2 before @

Yes, thats the one

On Wed, 10 Nov 2004 03:16:47 GMT, Chuck wrote:

Well do I have egg on my face!

Gary, you are correct, of course, in stating that there is not a lot of
difference between the vertical radiation patterns of half-wave and
quarter-wave antennas. Surely not the differences I was alluding to.

And so my statements to the contrary were just plain wrong.

While I was writing half-wave, I was thinking of something longer, like
3/4 wave. I should have been more careful and I do apologize.

My point, however, is just as valid. Many sailboats sport 45' backstay
antennas and that is close to 3/4 wavelength in the 15 MHz range. A 3/4
wave antenna has maximum vertical radiation at 45 degrees! I would say a
16- or even an 8-foot whip would be very competitive with such a
backstay antenna at the lower radiation angles needed for transoceanic
communication.

At higher marine frequencies, 3/4 wavelength is obviously even less than
45 feet.

Of course, the 3/4 wave will be efficient and easy on the autotuner.

I'll try to keep my brain in synch with my typing, henceforth.

Chuck


Hi Chuck,

That 3/4 wavelength antenna pattern you are looking at I will bet is
for a horizontal antenna 3/4 wave high. The pattern for a vertical
antenna is different. Also when you see antenna patterns that show
main lobe radiation angles you need to look closely at them to see how
many db down the signal really is at the desired angle. It does not
disappear entirely at any angle. Although there sharp notches in the
pattern at times where the signal is highly attenuated it is rare that
the signal is completely eliminated at that small angle.
Also with longer antennas, multiple lobes are created rather than a
single lobe as seen with a shorter antenna. Many times those multiple
lobes can be a help in filling in angles that may be otherwise missed.
Sometimes the nulls can work against you too.

With a sloping antenna such as a backstay, while the radiation angle
may be raised in one direction because of a long antenna it also is
lowered in the opposite direction because of the higher angle lobe.

On a boat you usually have little control of where the antenna goes
and the angle at which it runs.

The lowest radiation angle may not always be the best for the path you
are trying to work either. For very long distances low angles are
usually better but medium and shorter distances may be better with a
little higher radiation angle.

A note about the low frequencies:
If you are working surface wave communications below 3 mhz a vertical
antenna is essential. Only vertical polarization works in that mode
and is very reliable night and day over the given range.
Horizontally polarized signals cancel out and you get no surface wave
with them. AM broadcast stations are an example of this type of
propagation. Surface waves follow close to the earth on the low
frequencies. On higher frequencies they are quickly attenuated. I am
sure that Bruce can attest to the reliable communication on the low
band.

Doug's 23 foot whip may work very well on the higher bands as it is
more vertical than a backstay and probably more in the clear. But it
will not be a good performer on the lower bands.

Another note on short antennas: That 23 foot whip that Doug uses is
less than an 1/8 wavelength on 4 mhz.
A quarter wavelength vertical has a radiation resistance of around 36
ohms. Shorten it to an 1/8 wavelength and the radiation resistance
does not drop in half but goes down to around 6 ohms! That antenna
radiation resistance is in series with the ground system resistance
which is usually quite high. It may be in the order of 20 to 30 ohms
in many cases. Guess where most of the power goes.

Regards
Gary

Hello again, Gary. Thanks for your reply.

There are a few points still not settled. But first we need to separate
the objective importance of radiation at various vertical angles from
the objective reality of how much energy different antennas radiate at
these angles. There seems to be a reluctance among some in the group to
acknowledge that vertical radiation angles are important enough to
warrant an influence on antenna design decisions. I'm going to leave
that alone and just talk about how various antenna designs radiate.

My first "exhibit" is figures 54, 59, and 60 from the ARRL Antenna Book
(20th edition), Chapter 16. Vertical radiation patterns for a
quarter-wave, transom-mounted whip are compared with those for a typical
backstay antenna at 20 meters.

Figure 60 shows the backstay at 15 meters but there is no corresponding
quarter-wave whip figure for that frequency. Fortunately, however, we
are on fairly solid ground by assuming the vertical pattern of a
quarter-wave 15 meter whip will be quite similar to that of a
quarter-wave 20 meter whip. Thus, we can compare figure 54 to figure 60.

I believe that the ARRL patterns show the whip to be an unambiguously
better low-angle radiator than the backstay. From these patterns, I can
easily imagine situations in which the backstay would nonetheless be a
better choice. I can just as easily imagine situations in which the
quarter-wave whip would be a better choice. Just based on the vertical
radiation patterns alone.

But that's not all! The versatility of the backstay antenna at other
frequencies and the attendant complication of a tuner could be compared
to the simplicity of the whip, its physical independence from the mast,
and its lack of need for a tuner. These are other considerations that
might affect one's choice. Heck, they're not even mutually exclusive!
Just measurably different.

Regarding the alleged necessity of a vertical antenna for "surface wave
type communications," please consider the US Marine Corps' take on this
in their Antenna Handbook (MC RP 3-40.3C, page 4-40):

"NVIS propagation is simply sky wave propagation that uses antennas
with high-angle radiation and low operating frequencies. Just as
the proper selection of antennas can increase the reliability of a
long- range circuit, short-range communications also require proper
antenna selection. NVIS propagation is one more weapon in the
communicator’s arsenal.

To communicate over the horizon to an amphibious ship on the
move, or to a station 100 to 300 kilometers away, the operators
should use NVIS propagation. The ship’s low take-off angle
antenna is designed for medium and long-range communications.
When the ship’s antenna is used, a skip zone is formed. This skip
zone is the area between the maximum ground wave distance and
the shortest sky wave distance where no communications are possible.
Depending on operating frequencies, antennas, and propagation
conditions, this skip zone can start at roughly 20 to 30 kilometers
and extend out to several hundred kilometers, preventing communications
with the desired station.

NVIS propagation uses high take-off angle (60° to 90°) antennas to
radiate the signal almost straight up. The signal is then reflected
from the ionosphere and returns to Earth in a circular pattern all
around the transmitter. Because of the near-vertical radiation angle,
there is no skip zone. Communications are continuous out to several
hundred kilometers from the transmitter. The nearly vertical angle
of radiation also means that lower frequencies must be used. Generally,
NVIS propagation uses frequencies up to 8 MHz."

Sorry for the poor formatting. NVIS is what you get with a horizontal
dipole on the deck of a non-metal hull that I had mentioned. I really
doubt that you can get reliable daytime 3 MHz communication using 150
watt transmitters and antennas connected to 50 foot masts and at
distances of hundreds of kilometers. But with NVIS, it is routine.

The other point has to do with the vertical radiation pattern of a
3/4-wave vertical. You will agree, I believe, that the VERTICAL pattern
of the 3/4-wave vertical over perfect ground is "one-half" of the
HORIZONTAL pattern of a 1.5 wavelength dipole in free space. (Split the
dipole with a plane perpendicular to the wire's axis and then rotate the
plane through 90 degrees so the wire is vertical. You can throw away the
image beneath the plane to make it look like the usual patterns.) It
follows, then, that the lobe of the 3/4 wave antenna in the vertical
plane will peak at 45 degrees. Of course, over real ground the pattern
will be different. I doubt though that real ground will LOWER the
vertical radiation pattern. In any case, my statement has nothing to do
with the the height of a horizontal dipole above ground.

As an "exhibit" on this point, I offer a meager quote from Low Band
DXing (3rd edition), page 9-51:

Note that going from a 1/4 wave vertical to a
1/2 wave vertical drops the radiation angle from
26 degrees to 21 degrees. More important, however,
is that the 3-dB vertical beamwidth drops from 42
degrees to 29 degrees. Going to a 5/8 vertical drops
the radiation angle to 15 degrees with a 3-dB beamwidth
of only 23 degrees. But notice the high-angle lobe
showing up with the 5/8 wave vertical. If we make the
vertical still longer, the low-angle lobe will disappear
and be replaced by a high-angle lobe. A 3/4 wave vertical
has a radiation angle of 45 degrees.

So the humble contribution I've been trying to make is that longer
antennas are not always better than shorter ones. They are sometimes
better and sometimes worse. But they are always different. Whether the
difference is worth considering pretty much depends on the nature of the
difference.

Time to move on, I think.

Regards,

Chuck



















Gary Schafer wrote:
On Wed, 10 Nov 2004 03:16:47 GMT, Chuck wrote:


Well do I have egg on my face!

Gary, you are correct, of course, in stating that there is not a lot of
difference between the vertical radiation patterns of half-wave and
quarter-wave antennas. Surely not the differences I was alluding to.

And so my statements to the contrary were just plain wrong.

While I was writing half-wave, I was thinking of something longer, like
3/4 wave. I should have been more careful and I do apologize.

My point, however, is just as valid. Many sailboats sport 45' backstay
antennas and that is close to 3/4 wavelength in the 15 MHz range. A 3/4
wave antenna has maximum vertical radiation at 45 degrees! I would say a
16- or even an 8-foot whip would be very competitive with such a
backstay antenna at the lower radiation angles needed for transoceanic
communication.

At higher marine frequencies, 3/4 wavelength is obviously even less than
45 feet.

Of course, the 3/4 wave will be efficient and easy on the autotuner.

I'll try to keep my brain in synch with my typing, henceforth.

Chuck



Hi Chuck,

That 3/4 wavelength antenna pattern you are looking at I will bet is
for a horizontal antenna 3/4 wave high. The pattern for a vertical
antenna is different. Also when you see antenna patterns that show
main lobe radiation angles you need to look closely at them to see how
many db down the signal really is at the desired angle. It does not
disappear entirely at any angle. Although there sharp notches in the
pattern at times where the signal is highly attenuated it is rare that
the signal is completely eliminated at that small angle.
Also with longer antennas, multiple lobes are created rather than a
single lobe as seen with a shorter antenna. Many times those multiple
lobes can be a help in filling in angles that may be otherwise missed.
Sometimes the nulls can work against you too.

With a sloping antenna such as a backstay, while the radiation angle
may be raised in one direction because of a long antenna it also is
lowered in the opposite direction because of the higher angle lobe.

On a boat you usually have little control of where the antenna goes
and the angle at which it runs.

The lowest radiation angle may not always be the best for the path you
are trying to work either. For very long distances low angles are
usually better but medium and shorter distances may be better with a
little higher radiation angle.

A note about the low frequencies:
If you are working surface wave communications below 3 mhz a vertical
antenna is essential. Only vertical polarization works in that mode
and is very reliable night and day over the given range.
Horizontally polarized signals cancel out and you get no surface wave
with them. AM broadcast stations are an example of this type of
propagation. Surface waves follow close to the earth on the low
frequencies. On higher frequencies they are quickly attenuated. I am
sure that Bruce can attest to the reliable communication on the low
band.

Doug's 23 foot whip may work very well on the higher bands as it is
more vertical than a backstay and probably more in the clear. But it
will not be a good performer on the lower bands.

Another note on short antennas: That 23 foot whip that Doug uses is
less than an 1/8 wavelength on 4 mhz.
A quarter wavelength vertical has a radiation resistance of around 36
ohms. Shorten it to an 1/8 wavelength and the radiation resistance
does not drop in half but goes down to around 6 ohms! That antenna
radiation resistance is in series with the ground system resistance
which is usually quite high. It may be in the order of 20 to 30 ohms
in many cases. Guess where most of the power goes.

Regards
Gary

I believe that the ARRL patterns show the whip to be an unambiguously
better low-angle radiator than the backstay.

This might explain why I have had such good luck with a whip compared to
the backstay antenna I had on my previous boat.

But that's not all! The versatility of the backstay antenna at other
frequencies and the attendant complication of a tuner could be compared to
the simplicity of the whip, its physical independence from the mast, and
its lack of need for a tuner.

How do you get away without a tuner?

Doug
s/v Callista

On Wed, 10 Nov 2004 19:07:19 GMT, Chuck wrote:

Hello again, Gary. Thanks for your reply.

There are a few points still not settled. But first we need to separate
the objective importance of radiation at various vertical angles from
the objective reality of how much energy different antennas radiate at
these angles. There seems to be a reluctance among some in the group to
acknowledge that vertical radiation angles are important enough to
warrant an influence on antenna design decisions. I'm going to leave
that alone and just talk about how various antenna designs radiate.

They may be important but there is usually little you can do about it
on a boat.


My first "exhibit" is figures 54, 59, and 60 from the ARRL Antenna Book
(20th edition), Chapter 16. Vertical radiation patterns for a
quarter-wave, transom-mounted whip are compared with those for a typical
backstay antenna at 20 meters.

Figure 60 shows the backstay at 15 meters but there is no corresponding
quarter-wave whip figure for that frequency. Fortunately, however, we
are on fairly solid ground by assuming the vertical pattern of a
quarter-wave 15 meter whip will be quite similar to that of a
quarter-wave 20 meter whip. Thus, we can compare figure 54 to figure 60.

I believe that the ARRL patterns show the whip to be an unambiguously
better low-angle radiator than the backstay. From these patterns, I can
easily imagine situations in which the backstay would nonetheless be a
better choice. I can just as easily imagine situations in which the
quarter-wave whip would be a better choice. Just based on the vertical
radiation patterns alone.

They only show the vertical angle at an azmuth of 90 degrees. Don't
know if that is the best or worse direction for the vertical angle.

If you look closely at those patterns you willl see that the backstay
vertical pattern is much broader than the whip. That is an advantage
when working various distances that require different take off angles.

Very low angles are usually only good for very long haul
communications. Want to talk to China or Japan?
Shorter range, around the US, usually require higher angles to do the
job.

Talk to some of the hams that have stacked beams on tall towers. Often
the lower antenna, with it's higher take off angle is superior to the
higher antenna on shorter paths.

Also remember that just because the maximum of the lobe may be at 30
degrees, dosn't mean that it is dead at 15 or even 10 degrees. It may
only be down a couple of db at lower angles.



But that's not all! The versatility of the backstay antenna at other
frequencies and the attendant complication of a tuner could be compared
to the simplicity of the whip, its physical independence from the mast,
and its lack of need for a tuner. These are other considerations that
might affect one's choice. Heck, they're not even mutually exclusive!
Just measurably different.

A whip with no tuner is good for only one frequency. And then it
requires some sort of matching network to make it work. Might just as
well put in a tuner and make use of it on other frequencies too.


Regarding the alleged necessity of a vertical antenna for "surface wave
type communications," please consider the US Marine Corps' take on this
in their Antenna Handbook (MC RP 3-40.3C, page 4-40):

"NVIS propagation is simply sky wave propagation that uses antennas
with high-angle radiation and low operating frequencies. Just as
the proper selection of antennas can increase the reliability of a
long- range circuit, short-range communications also require proper
antenna selection. NVIS propagation is one more weapon in the
communicator’s arsenal.

To communicate over the horizon to an amphibious ship on the
move, or to a station 100 to 300 kilometers away, the operators
should use NVIS propagation. The ship’s low take-off angle
antenna is designed for medium and long-range communications.
When the ship’s antenna is used, a skip zone is formed. This skip
zone is the area between the maximum ground wave distance and
the shortest sky wave distance where no communications are possible.
Depending on operating frequencies, antennas, and propagation
conditions, this skip zone can start at roughly 20 to 30 kilometers
and extend out to several hundred kilometers, preventing communications
with the desired station.

NVIS propagation uses high take-off angle (60° to 90°) antennas to
radiate the signal almost straight up. The signal is then reflected
from the ionosphere and returns to Earth in a circular pattern all
around the transmitter. Because of the near-vertical radiation angle,
there is no skip zone. Communications are continuous out to several
hundred kilometers from the transmitter. The nearly vertical angle
of radiation also means that lower frequencies must be used. Generally,
NVIS propagation uses frequencies up to 8 MHz."

Sorry for the poor formatting. NVIS is what you get with a horizontal
dipole on the deck of a non-metal hull that I had mentioned. I really
doubt that you can get reliable daytime 3 MHz communication using 150
watt transmitters and antennas connected to 50 foot masts and at
distances of hundreds of kilometers. But with NVIS, it is routine.

The "surface wave" propagation that I was talking about, that requires
vertical polarization, is not the same thing. NVIS is still dependent
on ionosphere reflections and is at the mercey of the ionosphere.
Daytime may kill the signal.
With surface wave propagation it is there all the time, night or day.
It is what broadcast stations depend on. It is very usefull on the 2
mhz marine band with proper antennas. The signal follows the surface
of the earth rather than being reflected from the ionosphere.


The other point has to do with the vertical radiation pattern of a
3/4-wave vertical. You will agree, I believe, that the VERTICAL pattern
of the 3/4-wave vertical over perfect ground is "one-half" of the
HORIZONTAL pattern of a 1.5 wavelength dipole in free space. (Split the
dipole with a plane perpendicular to the wire's axis and then rotate the
plane through 90 degrees so the wire is vertical. You can throw away the
image beneath the plane to make it look like the usual patterns.) It
follows, then, that the lobe of the 3/4 wave antenna in the vertical
plane will peak at 45 degrees. Of course, over real ground the pattern
will be different. I doubt though that real ground will LOWER the
vertical radiation pattern. In any case, my statement has nothing to do
with the the height of a horizontal dipole above ground.

No, you can not just split the pattern of a horizontal antenna and
rotate it to get a vertical pattern. In free space yes, on the ground
no. The earth has a large effect on it. Reflections from the earth add
and subtract to determine the pattern.

If you look at the vertical patterns from a horizontal antenna at
different heights above ground you will see drastic changes in the
vertical pattern.
There is not a lot of information printed on vertical radiators of
different lengths. Folks often confuse the horizontal patterns with
what a vertical pattern would be.


As an "exhibit" on this point, I offer a meager quote from Low Band
DXing (3rd edition), page 9-51:

Note that going from a 1/4 wave vertical to a
1/2 wave vertical drops the radiation angle from
26 degrees to 21 degrees. More important, however,
is that the 3-dB vertical beamwidth drops from 42
degrees to 29 degrees. Going to a 5/8 vertical drops
the radiation angle to 15 degrees with a 3-dB beamwidth
of only 23 degrees. But notice the high-angle lobe
showing up with the 5/8 wave vertical. If we make the
vertical still longer, the low-angle lobe will disappear
and be replaced by a high-angle lobe. A 3/4 wave vertical
has a radiation angle of 45 degrees.

So the humble contribution I've been trying to make is that longer
antennas are not always better than shorter ones. They are sometimes
better and sometimes worse. But they are always different. Whether the
difference is worth considering pretty much depends on the nature of the
difference.

I agree. Large ships usually have several different types of
antennas. However, in most boat installations you usually only have
one shot at it. One antenna is all there is room for. I would opt for
as much wire as I could get up in that case. More wire will give much
improved performance on the low bands with a moderate compromise on
the high bands.


Time to move on, I think.

Regards,

Chuck


Regards
Gary

















Gary Schafer wrote:
On Wed, 10 Nov 2004 03:16:47 GMT, Chuck wrote:


Well do I have egg on my face!

Gary, you are correct, of course, in stating that there is not a lot of
difference between the vertical radiation patterns of half-wave and
quarter-wave antennas. Surely not the differences I was alluding to.

And so my statements to the contrary were just plain wrong.

While I was writing half-wave, I was thinking of something longer, like
3/4 wave. I should have been more careful and I do apologize.

My point, however, is just as valid. Many sailboats sport 45' backstay
antennas and that is close to 3/4 wavelength in the 15 MHz range. A 3/4
wave antenna has maximum vertical radiation at 45 degrees! I would say a
16- or even an 8-foot whip would be very competitive with such a
backstay antenna at the lower radiation angles needed for transoceanic
communication.

At higher marine frequencies, 3/4 wavelength is obviously even less than
45 feet.

Of course, the 3/4 wave will be efficient and easy on the autotuner.

I'll try to keep my brain in synch with my typing, henceforth.

Chuck



Hi Chuck,

That 3/4 wavelength antenna pattern you are looking at I will bet is
for a horizontal antenna 3/4 wave high. The pattern for a vertical
antenna is different. Also when you see antenna patterns that show
main lobe radiation angles you need to look closely at them to see how
many db down the signal really is at the desired angle. It does not
disappear entirely at any angle. Although there sharp notches in the
pattern at times where the signal is highly attenuated it is rare that
the signal is completely eliminated at that small angle.
Also with longer antennas, multiple lobes are created rather than a
single lobe as seen with a shorter antenna. Many times those multiple
lobes can be a help in filling in angles that may be otherwise missed.
Sometimes the nulls can work against you too.

With a sloping antenna such as a backstay, while the radiation angle
may be raised in one direction because of a long antenna it also is
lowered in the opposite direction because of the higher angle lobe.

On a boat you usually have little control of where the antenna goes
and the angle at which it runs.

The lowest radiation angle may not always be the best for the path you
are trying to work either. For very long distances low angles are
usually better but medium and shorter distances may be better with a
little higher radiation angle.

A note about the low frequencies:
If you are working surface wave communications below 3 mhz a vertical
antenna is essential. Only vertical polarization works in that mode
and is very reliable night and day over the given range.
Horizontally polarized signals cancel out and you get no surface wave
with them. AM broadcast stations are an example of this type of
propagation. Surface waves follow close to the earth on the low
frequencies. On higher frequencies they are quickly attenuated. I am
sure that Bruce can attest to the reliable communication on the low
band.

Doug's 23 foot whip may work very well on the higher bands as it is
more vertical than a backstay and probably more in the clear. But it
will not be a good performer on the lower bands.

Another note on short antennas: That 23 foot whip that Doug uses is
less than an 1/8 wavelength on 4 mhz.
A quarter wavelength vertical has a radiation resistance of around 36
ohms. Shorten it to an 1/8 wavelength and the radiation resistance
does not drop in half but goes down to around 6 ohms! That antenna
radiation resistance is in series with the ground system resistance
which is usually quite high. It may be in the order of 20 to 30 ohms
in many cases. Guess where most of the power goes.

Regards
Gary

Doug, it's difficult to generalize but in many cases the radiation
resistance of a whip will be in the range of 20 to 35 ohms (assuming the
whip is a quarter-wave or somewhat shorter) and the ground resistance in
series with that may be another 25 ohms or so. What you get is a
feedpoint impedance of about 45 to 60 ohms (could be more or less) which
will match 50 ohm coax very nicely without a tuner. Most transmitters
will feed loads of 25 to 100 ohms (2:1 swr) without complaining. For a
short run of coax, your total losses will probably be less than if you
used a tuner.

It is true that you can only use such an antenna for a single marine or
ham band. Even then, at the lower frequencies, you will experience a
limited band of frequencies that you can use without a tuner. On 8 MHz
and above, you will probably find that an antenna cut for the middle of
the band will cover the whole band nicely.

A lot of cruisers keep a 14 MHz "Hamstick" on board as an emergency
antenna they can use if their tuner fails or if (heaven forbid) they are
dis-masted and can't use their backstay antenna. In an emergency you can
check in to the Maritime Mobile Service Net on 14.300 MHz even if you're
not a ham. It is one of the few frequencies monitored almost
continuously by experienced operators. The Hamstick is easy to store,
easy to install, and once adjusted, should be trouble-free. To switch
bands, you switch Hamsticks. They even make a quick-connect gizmo.

There are other makes as well. But if you don't use something like a
Hamstick, and just use a longer whip like a 16 foot whip, it will be
good for just one band. Actually, 16 feet is close to a quarter-wave on
20 meters so you may be able to use it as-is without a tuner on that
band. If you're not comfortable doing the hookup, find a local ham to
advise you. They're usually glad to help.

Good luck!

Chuck


Doug Dotson wrote:
I believe that the ARRL patterns show the whip to be an unambiguously
better low-angle radiator than the backstay.


This might explain why I have had such good luck with a whip compared to
the backstay antenna I had on my previous boat.


But that's not all! The versatility of the backstay antenna at other
frequencies and the attendant complication of a tuner could be compared to
the simplicity of the whip, its physical independence from the mast, and
its lack of need for a tuner.


How do you get away without a tuner?

Doug
s/v Callista