Beverage Height?
Andrew J. O'Brien
it. I have 30 acres and plenty of room. I am thinking about using a line
of grapevines which conveniently have posts along the line, the grapevine
lengths are about 300 feet. They posts are only about 5FT high though ,
just wondering what the optimal height is ?
Bill Tippett
>
>> just wondering what the optimal height is ?
>
not noticed a significant difference. Most of mine have been 6' high so I
think 5' will work fine. However, Beverages should ideally be at least 1
wavelength long so yours may not work well on 160 but will be fine for higher
bands.
73, Bill W4ZV
Gray Frierson Haertig
>
> it. I have 30 acres and plenty of room. I am thinking about using a line
> of grapevines which conveniently have posts along the line, the grapevine
> lengths are about 300 feet. They posts are only about 5FT high though ,
I believe there is a reference for this in the ARRL Antenna Handbook.
This is not a real critical parameter, especially on beverages that are
not much longer than 1 wavelength. As the antenna height gets lower,
the velocity of propagation along the antenna slows down. (The antenna
forms an unbalanced transmission line to ground.) If the velocity gets
too slow, in long Beverages the current induced in the antenna is no
longer in step with the wavefront and you lose directivity.
It sounds like your 5 foot height, while not optimal, is certainly close
enough. IIRC, optimal height would be about 8 to 10 feet.
In general, Beverage antenas do best over ground with poor conductivity,
so a vineyard might not be optimal, but probably a whole lotta fun to
play around with anyway.
Tom Rauch had some good notes on matching Beverages in CommQuart a while
back. (Spring 97 ?)
Gray
--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
g...@haertig.com
Ken Brown
long wires or dipoles. A beverage's directional characteristic is due
in part to the proximity of the ground and the losses that causes.
Bill Tippett <btip...@ctc.net> wrote:
>> "Andrew J. O'Brien" wrote:
>>
>>> just wondering what the optimal height is ?
>>
K
For my beverages (1300' and 1000') I run them from tree to tree using
electrical fence insulators (nail in type). The height varies from about
5 - 7', and I do not run them in an exact straight line, but somewhat close
to a line.
Kent, NI9U
Andrew J. O'Brien wrote in message <7h6o3g$q59$1...@mica.netsync.net>...
>Was reading the post about Beverage antennas and am thinking about trying
>it. I have 30 acres and plenty of room. I am thinking about using a line
>of grapevines which conveniently have posts along the line, the grapevine
>lengths are about 300 feet. They posts are only about 5FT high though ,
Richard Harrison
Just wondering what the optimal height is?
"Electrical Communication Systems Engineering" (War Department TM
11-486, April 25, 1945) says:
"In the form suggested for tactical use, the wave (Beverage) antenna
consists of a single wire two or more wavelengths long, supported on
poles at a height of 12 to 20 feet above ground."
Best regards, Richard Harrison, KB5WZI
Roy Lewallen
quite well. (You have to use the Sommerfeld ground, called
"high-accuracy real" ground in EZNEC. The ground connection can be
simulated with several radial wires just above the ground -- I'd make
them about 1/8 free space wavelength long.) It would be interesting to
see what properties change as you change the height. Unfortunately, I
don't have time to do this just now, but maybe someone else would be
interested in giving it a shot.
Roy Lewallen, W7EL
Richard Harrison
The ground connection can be simulated with several radial wires just
Roy`s suggestion agrees with the War Department. They suggested a
"crowfoot", pointed at the target, constructed of three wires just above
the ground as a counterpoise. Obviously, little importance was placed on
the exact details of the ground system. If you could only make a ground
connection at the radio, that was OK too. A "good ground" was
recommended.
The input impedance is said to be reasonably constant (about 500 ohms)
with frequency when using a single elevated wire. This can be lowered by
using multiple elevated wires.
The Beverage is unidirectional when long and terminated in its
characteristic impedance at the far end. The beamwidth narrows as the
antenna lengthens in terms of wavelength. The War Department
prescription is for 2 to 2 and a half wavelengths which produces a more
or less continuous broad propagation lobe in the direction of the
termination resistor. This is said to be vertically polarized and the
equal of a 1/4 wave vertical antenna erected at the same site.
The Beverage is said to be a good transmitting antenna, but the
termination resistor has to be capable of dissipating 1/3 of the
transmitter power output when the antenna is two wavelengths long. If
the Beverage is used to transmit at frequencies where it is less than
two wavelengths, the termination resistor could be required to absorb
more than 1/3 the transmitter power. If this can`t be handled by the
termination resistor, the antenna will become bidirectional when the
resistor goes POOF!
You might look at KB1GW`s collection of Beverage Antenna Information at:
http://geocities.com/CapeCanaveral/1138/bev-page.html
Richard Harrison
The input impedance is said to be reasonably constant (about 500 ohms)
elevated wires.
500 ohms is about the impedance of a single long wire at a height of 12
to 20 feet.
The long wire is functioning as a wide-spaced, radiating, transmission
line which is unbalanced and uses the Earth as the other half of its
circuit.
Obviously, another way to reduce the surge impedance would be to lower
the elevated wire. The reduced line-spacing reduces impedance just as it
would in any transmission line.
The Beverage is similar to a vertical half-rhombic. The vertical rhombic
or half rhombic are vertically polarized antennas which operate as
radiating transmission lines or traveling wave antennas. The Beverage
antenna advantage is that no tall center support is needed. The Beverage
disadvantage is that the wide spread in the center of the rhombic
encourages much higher radiation than the uniformly spaced Beverage. The
radiation from the up and down slopes of the rhombic or half rhombic can
be aligned to give a large gain.
Nevertheless, any antenna only 12 to 20 feet high that can equal the
performance of a full quarter-wave vertical on the same site has
applications. The War Department suggested stringing an insulated wire
through the tree branches to make a Beverage that you could get on the
air quickly and effectively, and which would not be so conspicuous to
the enemy.
Gray Frierson Haertig
<snippity snip>
This is said to be vertically polarized and the
> equal of a 1/4 wave vertical antenna erected at the same site.
> The Beverage is said to be a good transmitting antenna, but the
> termination resistor has to be capable of dissipating 1/3 of the
> transmitter power output when the antenna is two wavelengths long. If
> the Beverage is used to transmit at frequencies where it is less than
> two wavelengths, the termination resistor could be required to absorb
> more than 1/3 the transmitter power. If this can`t be handled by the
> termination resistor, the antenna will become bidirectional when the
> resistor goes POOF!
>
>
> Best regards, Richard Harrison, KB5WZI
I'd be hard pressed to believe that a 2 wavelength long wire that is a
very small fraction of a wavelength above a lossy ground would have
anywhere near the efficiency of a 1/4 lambda vertical monopole with a
proper ground system. Especially if you are planning on burning up 1/3
of the power in a resistor!
Even considering the directivity of the beverage over the vertical, I
doubt that the radiated power in the desired direction is greater than
that of an omni-directional vertical.
As a receive antenna, it would considerably outperform the vertical
because of its directivity. Efficiency isn't a consideration for
receive purposes at HF.
Having said all of this, I don't have proof of it other than virtually
every reference I've read states that a Beverage is a poor transmit
antenna.
Richard Harrison
..virtually every reference I`ve read states that a Beverage is a poor
transmit antenna.
That is what I`ve read too. But in nearly all instances with antennas,
reciprocity rules. I think the War Department was only considering the
Beverage`s effectiveness as a point-to-point communications device and
not its radiation efficiency as a broadcast device in all directions.
Here are are their exact words:
The component due to wave tilt is larger over poor earth than over good
earth; over sea water it is very small. The wave antenna, because of
these properties and because of its fairly high impedance, can be used
to advantage over rocky or sandy soil, where difficulty in obtaining a
low-resistance ground connection decreases the efficiency of
low-resistance antennas such as short whips or quarter-wave antennas.
With two wave-lengths of wire, an efficiency equalling that of a
quarter-wave vertical can be expected in the h-f band over poor or
medium soil. This antenna should not be used over salt marsh or sea
water.
Perhaps I should have given all that quotation in my first posting. But
I sought only to answer the question of the best height to place the
Beverage above ground, which the War Department said was 12 to 20 feet.
The authors of "Electrical Communication Systems Engineering" are not
identified. It was produced in serious circumstances for very serious
purposes when the accuracy of its information could mean life or death.
I have found no mistakes even though its scope is encyclopedic. A lot of
the text is similar to issues from "Bell Telephone Labs". Some of the
text is similar to the issues of the "M.I.T. Radiation Labs". The
simiarities are probably more than circumstantial or coincidental.
As for suitability for transmitting from a Beverage, the War Department
said:
"This antenna is directional and is used for either transmitting or
receiving vertically polarized ground waves. Maximum response or
radiation is in line with the wire and off the terminated end, with
little response or radiation in the opposite direction or broadside, if
properly terminated. The forward lobe may be made narrower and the gain
increased by using several wavelengths of wire."
In short, I think what the writers meant by saying the Beverage was the
equal of the 1/4-wave vertical was that the received signals were the
same between two points, but the Beverage antenna on each end of the
path is oriented to maximize the received signal. It is also assumed
that the antennas are working with poor soil conductivity. The
Beverage`s directional gain offsets it`s height disadvantage as compared
with the quarter-wave vertical antenna.
As I said, this is an encyclopedic volume and I am no typist. To get
some real gain over the Beverage, the War Department suggests a
ballon-supported half-rhombic (inverted vee, not the drooping dipole
type but end-driven lomg-wire type) antenna. They say that like the
Beverage, the half-rhombic is a good ground-wave launcher but provides a
large gain.
Maybe someone will report experiences with a transmitting Beverage. My
experience is with rhombics which are similar in wideband constant
impedance characteristics and directional response. But, the rhombic
can produce sizzling gain.
Frank Donovan
used to this day -- by special forces where a field expedient antenna with
directivity is necessary to minimize the probabability of being intercepted
by opposing forces.
73
Frank
W3LPL
dono...@erols.com
Richard Harrison wrote in message
<4900-373...@newsd-111.bryant.webtv.net>...
Richard Harrison
A beverage antenna is an inefficient antenna.
The War Department did not say that the Beverage is efficient. It said:
"With two wave-lengths of wire, an efficiency equalling that of a
quarter-wave vertical can be expected in the h-f band over poor or
medium soil."
Do you have data to contradict this War Department statement?
Ken Brown
>Gray Frierson Haertig wrote:
>..virtually every reference I`ve read states that a Beverage is a poor
>transmit antenna.
>That is what I`ve read too. But in nearly all instances with antennas,
>reciprocity rules.
A beverage antenna is an inefficient antenna. Yes reciprocity rules,
and so it is inefficient both for transmitting and for receiving. The
noise level on the low bands is such that for receiving purposes you
can afford to lose 10 or 20 dB of receive signal, because the noise
level (on an efficient antenna) is 10 or 20 dB above the noise floor
(that is the noise when the receiver is connected to a non antenna
resistive termination, or dummy load, almost the same if you just
short the input of the receiver) of a good receiver. For transmitting
most of us are not willing to use an antenna of such low efficiency.
I think the War Department was only considering the
>Beverage`s effectiveness as a point-to-point communications device and
>not its radiation efficiency as a broadcast device in all directions.
>Here are are their exact words:
>The component due to wave tilt is larger over poor earth than over good
>earth; over sea water it is very small. The wave antenna, because of
>these properties and because of its fairly high impedance, can be used
>to advantage over rocky or sandy soil, where difficulty in obtaining a
>low-resistance ground connection decreases the efficiency of
>low-resistance antennas such as short whips or quarter-wave antennas.
>With two wave-lengths of wire, an efficiency equalling that of a
>quarter-wave vertical can be expected in the h-f band over poor or
>Best regards, Richard Harrison, KB5WZI
Ken Brown
>Ken Brown, N6KB wrote:
>A beverage antenna is an inefficient antenna.
>The War Department did not say that the Beverage is efficient. It said:
>"With two wave-lengths of wire, an efficiency equalling that of a
>quarter-wave vertical can be expected in the h-f band over poor or
>medium soil."
>Do you have data to contradict this War Department statement?
No I do not. Do you have data to support that statement? It is
contrary to all I have ever heard or read about Beverages. I don't
have data that proves it incorrect however. Was the War Department
referring to "two wave-lengths of wire" not very high above ground as
(which is what I understand that a Beverage is) or is this statement
referring to a long wire antenna, whic is usually as high above ground
as can be conveiniently accomplished, with trees, utility poles or
other tall supports.
Richard Harrison
Was the War Department referring to "two wave-lengths of wire" not very
statement referring to a long wire antenna, which is usually as high
above ground as can be conviently accomplished---?
The War Department specified a hieght of 12 to 20 feet for h-f use. That
is about 5 meters, to use at wavelengths of 100 meters or less. This is
very low at 3 MHz, but is 1/2 wavelength at 30 MHz. I believe the War
Department expected the Beverage would be used for groundwave
propagation over relatively short distances at the low end of the h-f
range. Groundwaves dissipate rapidly at the high end of the h-f range.
The War Department Beverage is not the barbed-wire fence variety. It is
the part of an abandoned telephone line, or insulated wire strung
through tree limbs type of antenna. Very low Beverages are probably
unsuitable for transmission competition with the 1/4-wave vertical which
the War Department said its Beverage equals over poor-conductivity or
medium-conductivity soil.
Ken Brown
>Ken Brown, N6KB wrote:
>Was the War Department referring to "two wave-lengths of wire" not very
>high above ground as (which I understand that a Beverage is) or is this
>statement referring to a long wire antenna, which is usually as high
>above ground as can be conviently accomplished---?
>The War Department specified a hieght of 12 to 20 feet for h-f use. That
>is about 5 meters, to use at wavelengths of 100 meters or less. This is
>very low at 3 MHz, but is 1/2 wavelength at 30 MHz.
At this height I'd call it a low longwire and not a beverage.
Richard Harrison
At this height (12 to 20 feet) I`d call it a low longwire and not a
Beverage.
The other name for a Beverage is the "wave antenna". This is a clue to
the Beverage`s distinguishing characteristic, A wave antenna operates as
a radiating transmission line, a number of wavelengths long. Such
antennas are terminated in Z0 to provide unidirectional transmission and
reception.
The Beverage is an unbalanced transmission line, with a wire mounted low
enough so that the earth serves as the other half of the transmission
line, and preserves an impedance of about 500 ohms at the War
Department`s recommended height. This Z0 is frequency insensitive just
as any transmission line would tend to be, but there are some
differences because the wave antenna is certainly not a lossless line.
The beverage uses the wave tilt provided by the lossy earth for its
superior groundwave performance. That might not be the case with any old
long wire.
Richard Harrison
with Beverage wave antennas. In retrospect, I have had experience with
an equivalent of a Beverage. It was a h-f rhombic with about 1000 feet
of 600 ohm open wire line all laid out in a more or less straight line.
The rhombic was several hundred feet long at about 70 feet. The
transmission line was suspended at about 7 or 8 feet.
The rhombic had been erected as a last ditch program source if all else
failed to deliver programs to the shortwave broadcasting plant in
Portugal where I worked in the 1950`s. It was aimed at New York. The
transmission line ran to a screened room in the broadcast plant. I had a
switch installed at the antenna and a second line run to my house on the
plant site. I had a SP-600 which gave me great SW reception from the
states.
After the European broadcasters went silent around midnight, I liked to
listen to medium wave broadcasts from the states. The rhombic was too
small to deliver good medium wave performance. I found that shorting the
transmission line and using it as an antenna against ground worked fine.
I even had manual diversity reception. My favorite program was Edward R.
Murrow with the CBS news. Evening news time in New York was Midnight in
Europe.
WCBS ran 50 KW nondirectional at 880 KHz. WWL ran 50 KW East/West
directional at 870 KHz from New Orleans and duplicated the Murrow
broadcasts from WCBS in New York.
In Portugal both stations delivered good signals of about the same
strength. When one station faded, I just shifted 10 KHz and the other
station would nearly always be shaking the aether on my path with its
power. Under the circumstances, the reception was quite satisfactory. I
would stay up and "listen to Murrow tomorrow".
The long, though less than two wavelengths, wires of the transmission
line and its attached short circuited rhombic acted as a less than ideal
Beverage antenna. I have no quantitative data, but can report
qualitatively that it worked like gangbusters.
Gray Frierson Haertig
>
> Ken Brown, N6KB wrote:
> At this height (12 to 20 feet) I`d call it a low longwire and not a
> Beverage.
>
> The other name for a Beverage is the "wave antenna". This is a clue to
> the Beverage`s distinguishing characteristic, A wave antenna operates as
> a radiating transmission line, a number of wavelengths long. Such
> antennas are terminated in Z0 to provide unidirectional transmission and
> reception.
>
And, of course, the maximum on a Beverage is at right angles to the
maximum for a longwire.
However, what this really points out is that longwire antennas (whether
end fed or center fed) that are not at least 1 lambda above ground don't
really have very much directivity. This is why all the effort at
cutting antennas to length and orienting them in certain directions is a
waste of time for 90% of the SWL antennas out there. Most are just too
low and too close to other conducting objects to have any predictable
directivity. Not to say that some dedicated souls don't have the real
estate and the wherewithall to install SWL antennas with useable and
predictable directivity.
A wire antenna that is multiple wavelengths long will show a change in
directivity as it's height is increased, with directivity along its
length predominating at lower elevations (expressed in wavelengths), and
something else (multi-lobed) at higher elevations.
The elevation of a Beverage also affects the speed of propagation along
the wire. For Beverages of several wavelength length, if the elevation
of the wire is too low, the speed of propagation along the wire becomes
significantly slower than the speed of propagation of the wave front, so
the wave front no longer properly reenforces the signal in the wire.
This leads to a loss of gain (directivity). Even at an optimum
elevation, Beverages over a few wavelengths long don't show any increase
in directivity.
In a related matter. I did some web searches on Beverage antennas a
couple of years ago and came across a description of some research done
for Candaian Forces using arrayed Beverages at HF as part of and
over-the-horizon radar system. Interesting stuff. Sorry I haven't
saved the URL.
Richard Harrison
---and, of course the maximum on the Beverage is at right angles to the
maximum for a longwire.
I think the word "dipole" should be substituted for the word "longwire"
in the sentence above.
Beyond 1/2-wavelength, polarity reverses in a wtre and destructive
interference starts to take place in its radiation field. Lobes emerge
at an angle other than 90-degrees to the wire axis.
The horizontal wire must be remote from earth for pronounced directional
characteristics to appear, at all, in shortwire antennas. A low 1/2
wavelength dipole is essentially an omnidirectional radiator of
high-angle waves.
The longwire antenna remote from earth, produces those roseate (X)
patterns with respect to the wire azis. Close to earth, the longwire
antenna produces an end-fire groundwave.
All of this agrees with what Gray said, I believe, except that I would
infer that the maximum radiation for a longwire was perpendicular to the
wire from: "---the maximum on a Beverage is at right angles to the
maximum for a long wire." We know that the Beverage is an end-fire
antenna.
The radiation from an elevated longwire antenna is neither end-fire nor
broadside. That is why the arrays that combine radiation to give gain
from two or more long elevated wires are formed into vees and diamonds.
These forms allow the maxim radiations from the wires to coincide.
Richard Harrison
was a poor transmitting antenna. That agrees with what I`ve read except
for the War Department publication.
I`ve found my missing copy of Terman and Dr. Fred says:----mounted at a
convenient height (usually 10 to 20 feet) above earth. The wave antenna
(beverage) is suitable only for reception. In transmitting, the earth
losses are so great compared with the radiated energy that the low
efficiency more than counterbalances the directivity obtained.
The War Department and Terman reach opposite conclusions on the
Beverage`s suitability as a sending antenna.
Terman credits Harold H. Beverage, Chester W. Rice, and Edward W.
Kellog, and their publication:"The Wave Antenna-A New Type of Highly
Directive Antenna", Trans. A.I.E.E., 1923, for his information.
The War Department`s information was published 22 years after the
A.I.E.E. paper and may contain newer information about altered
conditions of the Beverage. However, antenna height recommendations are
nearly the same, 10 to 20 feet from Terman, and 12 to 20 feet from the
War Department. Length was two or more wavelengths.
Accurate tests and measurements could determine whether the Beverage is
really useful as a transmitting antenna, "as good as a 1/4-wave vertical
over poor soil".
Frank Donovan
US Special Forces use Beverage antennas in the field for both transmitting
and receiving
on strong-signal one-hop propagation paths. They offer very low profile,
field expediency
and directivity that reduces the probability of being intercepted or jammed
by opposing forces.
J. Litva and B.J. Rook in "Beverage Antennas for HF Communications,
Direction Finding and
Over-the-Horizon Radar, Communications Research Centre , 1976" provided
extensive
measurements made on the performance of individual Beverage antennas and
small to large
arrays of Beverages. with an aircraft towing a transmitting dipole
(XELEDOP).
A Beverage antenna 110 meters long and one meter high had the following
measured
parameters (the following quoted from the publication):
Power gain 0 dBi
Directive gain 18 dB
Azimuthal beamwidth 40 degrees
Vertical beamwidth 20 degrees
Sidelobes: typically down 15 to 25 dB with respect to the main beam
Take-off angle: 15 degrees
The discrepancy between the Beverage antenna's directive gain and power gain
is caused by its
low efficiency, typically less than two percent. As has often been pointed
out in the
literature, the main disadvantage of the Beverage antenna is its low
efficiency.
Litva and Rook also found that the side and back lobes were reduced by over
7 dB with respect to the main beam when the Beverage antenna height was
reduced by
from 1.7 meters to 0.3 meter. On the other hand, the losses in the antenna
were
increase by 10 dB at this low elevation.
Regards,
Frank
W3LPL
dono...@erols.com
Richard Harrison wrote in message
<9507-374...@newsd-112.bryant.webtv.net>...
Richard Harrison
US Special Forces use Beverage antennas in the field for both
The Beverage is not the only antenna which has low efficiency over lossy
ground. A look at the 1/4-wave vertical`s radiation versus elevation
angle over lossy soil shows why the Beverage is its equal. Low-angle
radiation from the 1/4-wave vertical is almost non-existent over lossy
ground. The figures which show this are in recent editions of the ARRL
Handbook.
Richard Clark
<dono...@erols.com> wrote:
>Richard,
>
>US Special Forces use Beverage antennas in the field for both transmitting
>and receiving
>on strong-signal one-hop propagation paths. They offer very low profile,
>field expediency
>and directivity that reduces the probability of being intercepted or jammed
>by opposing forces.
>
>J. Litva and B.J. Rook in "Beverage Antennas for HF Communications,
>Direction Finding and
>Over-the-Horizon Radar, Communications Research Centre , 1976" provided
>extensive
>measurements made on the performance of individual Beverage antennas and
>small to large
>arrays of Beverages. with an aircraft towing a transmitting dipole
>(XELEDOP).
>
>A Beverage antenna 110 meters long and one meter high had the following
>measured
>parameters (the following quoted from the publication):
>
>Power gain 0 dBi
>Directive gain 18 dB
>Azimuthal beamwidth 40 degrees
>Vertical beamwidth 20 degrees
>Sidelobes: typically down 15 to 25 dB with respect to the main beam
>Take-off angle: 15 degrees
>
Lacking the operating frequency makes the following speculative.
I chose as that operating frequency, 15 MHz, to approach the figures
above. For EZNEC, per the various recommendations (crow foot ground
radials located 1 cm above a high accuracy ground, average ground
type):
Fo: 15 MHz
Height: 1 M
Gain: 0.14 dBi
Vert B/W: 18.3 deg.
Az B/W: 32.6 deg.
Sidelobes: down 10 - 15 dB
Take-off: 17 deg.
>
>The discrepancy between the Beverage antenna's directive gain and power gain
>is caused by its
>low efficiency, typically less than two percent. As has often been pointed
>out in the
>literature, the main disadvantage of the Beverage antenna is its low
>efficiency.
>
>Litva and Rook also found that the side and back lobes were reduced by over
>7 dB with respect to the main beam when the Beverage antenna height was
>reduced by
>from 1.7 meters to 0.3 meter. On the other hand, the losses in the antenna
>were
>increase by 10 dB at this low elevation.
>
by lowering the model employed for EZNEC above to the suggested 30 cM:
Fo: 15 MHz
Height: 30 cM
Gain: -2.5 dBi
Vert B/W: 17.3 deg.
Az B/W: 30 deg.
Sidelobes: down 15 - 20 dB
Take-off: 15 deg.
>
>
>Regards,
>Frank
>W3LPL
Hi All,
by raising the model employed for EZNEC above to a "typical" 5 M:
Fo: 15 MHz
Height: 5 M
Gain: 4.25 dBi
Vert B/W: 21 deg.
Az B/W: 42 deg.
Sidelobes: down 4 - 10 dB
Take-off: 21 deg.
Again, all speculation when Fo is chosen to conform to the data.
However for the purposes of comparison, this frequency is certainly
within the general description for a Beverage antenna. It also
conforms to the observed performance for such variations in height.
The ground consisted of three radials in a 0, +45 deg, -45 deg layout
with the 0 deg toe extending completely out to the termination
resistor (110 M down the pike). The length of the other two had
little impact between being 1/10 wl to 1 wl long. Their affect was
found in the drive point Z where they contributed more to the X (-190
to -90 Ohms) as the R was dominated by the other half of this leaky
transmission line. The R tracks between 300 to 700 Ohms depending on
height. With a matching load at the far end, that load presented a
system loss of 1 to 1.5 dB.
For the "tall" 5 M implementation:
Dropping the Fo to 7.5 MHz brings down the gain of the forward lobe to
roughly 0 dBi with a take-off of 29 deg. All sidelobes are found
roughly 10 dB below.
Dropping further to 3.75 MHz brings down the gain of the forward lobe
to roughly -4.8 dBi with a pitiful take-off of 43 deg. Sidelobes are
also poor performers at barely 5 dB below this.
All in all, this modeling conforms to both expectations and reported
performance. It bears out the recommendation for being longer than 1
wavelength (typically 2; here up to 5 1/2). It also exhibits a rather
constant Z with some, but not much power lost to the termination (your
mileage may vary).
Another distinction is in the naming of this class of antenna. I've
seen the term "slow wave," but I have observed it is more frequently
known as a "traveling wave" antenna (as distinct from a "standing
wave" antenna, a term infrequently applied to dipoles and such). This
class is distinct in its being broadband and exhibiting waveguide or
transmission line qualities. The term "traveling wave" is also widely
applied to di-electric antennas (especially artificial, di-electrics),
a subject that is typically handled poorly here in this group.
73's
Richard Clark, KB7QHC