Vol 2, Number 2 July 2021
It’s hard to believe that July 1 st has come and gone – although not quite completely gone – and another membership year is upon us.
As you know, there are changes being made at our Main Site and while the final documents have yet to be signed, changes will be
occurring. At this point, we’re very optimistic that our footprint will change very little, and life should continue as we’ve known it for
years. But it does bring into the conversation the matter of what happens if we needed to make more significant changes. What
would those changes be and at what cost to accomplish them? How would we maintain our wide area coverage? What equipment
alterations might be needed? Would a new site require more expense? All these, and many more, of course, would require careful
consideration.At the end of the day, MAARS is committed to maintaining the best site possible for all
members. We have enjoyed a history of wide-area coverage and have included new
technologies whenever possible. Those are some of the attributes we vow to continue. So,
with that as a backdrop, if you have not already submitted your dues for the 2021/2022 year,
please do so now.
As I look at the current roster, there are some who, during the Covid era, did not renew during
the 2020/2021 year and we’d love to see you come back. We know it takes funds to keep
things running smoothly and it will take all of our help to make the changes we suspect are on
the horizon. So please, help us defray these costs with your dues.
Current Dues Structure
Join During Individual Family Senior
July $20.00 $25.00 $15.00
Aug $18.00 $23.00 $14.00
Sep $16.00 $21.00 $13.00
Oct 14.00 $19.00 $12.00
Nov $12.00 $17.00 $11.00
Dec $10.00 $15.00 $10.00
Jan $28.00 $33.00 $24.00
Feb $26.00 $31.00 $23.00
Mar $24.00 $29.00 $22.00
Apr $20.00 $25.00 $15.00
May $20.00 $25.00 $15.00
Jun $20.00 $25.00 $15.00
Tech & Tower
A huge shout out to Loren Jenz, N9ENR for his contribution to this edition of the Newsletter. Loren agreed to write a couple of articles about antennas and I know you’ll find them very interesting. In his first submission, he has laid out some basic technical
information on which he will build and refer to as this continues. Please let us know how you like this submission and, as always, if you have a question we can answer, or, if you’d like to submit something to share, please let me know.
Antenna Basics – Part 1
I was asked to write a series of articles for this newsletter. After thinking about it for a time, I thought that one of the subjects I could write about would be antennas. But there is a lot of information about antennas already available for the Amateur Radio operator.
So, I thought that maybe a simple non-theoretical, non-mathematical, or basic getting started approach would be the way to go. This approach would show the differing parts of many types of antennas along with short explanations of the functions of the individual
parts of antennas and types of antennas. Once these basics are learned, the reader can then refer to other literature about antennas to dig deeper into the theoretical and mathematical aspects of antennas. Or the reader can simply use the knowledge given here
in these articles to gain a basic understanding that will be useful for selecting and installing antennas.
In this inaugural article, the most important part of the antenna will be explained. That is the part of the antenna where the transmission line coming from a transceiver is connected. The dipole element or driven element will be explained and some of the variations in how the transmission line connects to the dipole will be shown. Also, the radiation pattern and the polarization of a dipole will be discussed.
An antenna is a device or structure that converts electrical signals to radio waves. It also converts radio waves into electrical signals which is the opposite function. In the first example, converting electrical signals into radio waves, the antenna is being used for
transmitting, and in the second example, the antenna is being used for receiving. The
antenna is basically a type of electrical transducer that converts electrical signals into radio
waves or radio waves into electrical signals. The antenna even has the ability to perform
these two functions at the same time. Before explaining antennas, a quick crash course in
transmission lines is needed.
Transmission lines, for the most part, fall into three categories: waveguide, coaxial, and
twinlead. The waveguide type of transmission line is rarely used in Amateur Radio and will
not be discussed here. Of the other two types, coaxial and twinlead, coaxial is the most
common. Coaxial or coax has the signal on the center conductor of the coax cable which
is shielded by the second conductor being tubular in construction and surrounding the
center conductor with an insulating material placed between them. The shield conductor,
which is simply referred to as the shield, is also the return ground for currents in the center
conductor and is the familiar second conductor in most simple electrical circuits involving
two wires. Signals present on a coax cable are referred to as unbalanced because there is
only one signal present on the center conductor.
When there are two signals present, each an exact copy of the other, but one of the
signals is 180 degrees out of phase with the other, then the signals present are referred to
as balanced. This is the third type of transmission line: the twinlead. Here two identical
conductors are held precisely spaced by an insulating material over the entire distance of
the transmission line. When the signal that is present on one wire is in its positive half
cycle, the signal present on the other wire is in its negative half cycle.
The vast majority of modern-day transceivers have an unbalance coaxial connector for
connecting the transmission line that goes to the antenna. A device called a balun can be
used to convert coaxial transmission line to the twinlead transmission line. The balun
works in both directions, so it can also be used to go from twinlead to a coaxial
transmission line. And, even more importantly, the balun can also change the impedance.
More will be discussed about impedance in the paragraphs below.
With this basic understanding of the types of transmission lines, the discussion will now
briefly turn to the simplest form of antenna. The simplest antenna is called a dipole or
dipole element. The basic dipole is an electrical conductor that has a length of what is
called a 1/2 wavelength. This means that the length of the dipole electrical conductor is
going to be determined by the desired operating frequency. The wavelength of a signal is
equal to the distance that the signal travels at the speed of light in only one cycle of the
signal. If the desired operating frequency is 300 MHz, then one cycle of that signal would
be only 1 Meter long or about 39 inches. Therefore, the length of dipole antenna needed
to operate at 300 MHz would be half that 1 Meter or 19 and 1/2 inches or 1 ft and 7-1/2
inches. For simplicity, the “468” formula is used by most amateurs to calculate the length
of the dipole at any frequency in MHz which then gives a result directly in feet:
468 / Frequency in MHz = The length of the dipole in feet.
For the above example: 468 / 300 MHz = 1 ft and 6-3/4 inches.
Please take notice of the shorter distance when the 468 formula is used. The difference is
due to something called the velocity factor which the 468 formula above takes into
account. When an electrical signal travels in an electrical conductor such as the dipole, it
travels slightly slower than the speed of light in a vacuum. The same is true for the
transmission lines discussed above, but for the transmission lines, the insulating material
used to separate the conductors can also have an effect on the velocity factor. This
insulating material in the transmission lines is also referred to as a dielectric.
Figure 1 shows the most basic of all dipoles. It is further cut in half into two 1/4 wavelength
conductors, and a small insulator is placed between the two conductors to keep them
electrically isolated from one another. This type of dipole is often referred to as a center
fed dipole. A 72-ohm unbalanced coax transmission line connects to the center of the
dipole as shown in figure 1.
Not shown in the diagram of course is the radio on the other
end of the coax. Having shown the simplest form of antenna, the dipole, a brief return to
some other subjects involving transmission lines is needed.
The first thing that is kind of strange about the dipole in figure 1 is why the 72-ohm coax. A
dipole as it is drawn in figure 1 has an impedance of 72 ohms and not the familiar 50 ohms
of the coax most often used by Amateurs. If the dipole in figure 1 is more than 1/4
wavelength from any surrounding objects or the earths surface, the antenna will have a
resistive only impedance of 72 ohms at the frequency of operation when transmitting. This
resistive only load of 72 ohm represents a conversion of the electrical signal not to heat but
into radio waves. When receiving, the load on the transceiver end of the 72-ohm coax will
need to be a 72-ohm resistive only impedance. If these conditions are not met, then there
is a mismatch and there will be reflected energy or a reflected signal present on the
transmission line.
In the case of transmitting, conditions not met would include: operating at some other
frequency the length of the dipole was not cut for, or, having objects at a distance of less
than 1/4 wavelength from any part of the dipole or antenna. Moving above or below the
frequency for which the dipole has been cut, will cause the 72-ohm impedance to change.
The impedance will usually have an accompanying inductive or capacitive reactance along
with some resistive component as well. The space around a dipole that is in the first 1/4
wavelength of the antenna is called the near field. Any objects inside the near field of a
dipole or an antenna become part of the antenna system. Any objects or materials that are
insulators less so, and any objects or materials that are conductors more so. Under these
conditions of having objects in the near field while the frequency is at the frequency for
which the dipole has been cut, the impedance will again have an accompanying inductive
or capacitive reactance along with some resistive component.
When either of these two types of undesirable conditions occur, there is reflected energy
on the transmission line, and this is referred to as either a high SWR (Standing Wave Ratio)
or high reflected power. All Amateurs are familiar with this and how, if allowed to get bad
enough, these conditions can damage a transmitter or RF power amplifier.
When these conditions exist while receiving with an antenna, they are referred to as return
loss: although it is not uncommon in some circles to hear the term return loss when
referring to a bad SWR in a transmit setting as well. The best example of return loss are
people who have used shortwave radios with a long wire as an antenna. Most shortwave
radios have a pre-selector or antenna tune control on them. This control or these controls
have to be adjusted for maximum loudness or maximum signal level whenever the receive
frequency is changed. The loading or impedance of the receiver antenna input connection
as seen by the antenna is being adjusted to some value other than 72 ohms resistive only.
The pre-selector or antenna tune control adjustments include not only changes in the
resistive loading but the inductive or capacitive reactance as well. This allows a static
unchanging structure, in this example a long wire antenna, to be used over a very wide
range of frequencies.
The same is true for transmit. A device called an antenna tuner can be placed in the
transmission line between a transceiver and an antenna to remove the bad SWR or high
reflected power. This same device improves reception signal levels as well by acting as a
receive preselector. Many modern-day Amateur Radio transceivers have a built-in antenna
tuner that can be used to achieve a good match (a low SWR) as seen by the transceiver’s
transmitter allowing the transmitter to operate safely without damage. Remember, that
transceiver built in antenna tuners have a limited or narrow range for SWR correction. Also
remember that even though the transmitter no longer sees a bad SWR once the tuner has
tuned, the bad SWR still exists on the transmission line.
One last comment about transmission lines before moving on to the subject of this article.
If a dipole antenna has an impedance of 72 ohms, what happens when the normal 50-ohm
transmission line is connected between the transceiver and the dipole? The answer is that
the change in the resistive only impedance from 72 ohms to 50 ohms has only a small
impact on the SWR with a low SWR of about 1.3 to 1. Most Amateurs use their transceiver’s
auto tune feature to make sure that the transmitter in the transceiver sees a 1.0 to 1 SWR,
but this SWR 1.3 to 1 is so low that it isn’t really that much different than a 1.0 to 1 SWR, so
tuning it out is optional.
Because this series of articles is about antenna basics, the discussion above about
transmission lines, SWR, reflected power, and return loss were discussed in a very limited
manner. It is very difficult to have a discussion about antennas and completely ignore
these subjects. The discussion above is more complex than what has been discussed here,
and it is recommended the reader investigate in more detail by reading other Amateur
Radio literature. It is also recommended the reader research baluns. Baluns have become
even more popular in recent years with their additional use in limited space HF multiband
antennas.
Before continuing on with figure 2, it would be helpful to use the 468 formula above to
calculate the lengths of dipoles for various Amateur Radio bands to give the reader a feel
for what kind of lengths dipoles can be. Below are shown the lengths of 1/2 wave dipoles
for four different Amateur Radio bands:
160 Meter band 468 / 1.8 MHz = 260 ft.
10 Meter band 468 / 28 MHz = 16ft 8-1/2 inches.
2 Meter band 468 / 144 MHz = 3ft 4 inches.
23 Centimeter band 468/ 1240 MHz = 4-1/2 inches.
As can be seen the variations in length are quite amazing. From the data about length, it is
easy to see that the length of a 1/2 wave dipole decreases with increases in frequency. This
rule not only holds true for the dipole, but it also holds true for almost all the antennas that
will be discussed in future articles. (The exception is the parabolic dish antenna for which it
is possible to have the same diameter dish for a multitude of different frequencies. The
parabolic dish will also be explained in a future article.) It is easy to see why a dipole is the
antenna of choice for the lower frequencies. More complex antennas that have other
elements besides the dipole would become physically large if implemented at the lower
Amateur Radio frequencies. More complex antennas that have other elements besides a
dipole element will be discussed in future articles.
Figure 2 shows four different variations of a dipole. This is only a sampling: there are many
more. At the top of figure 2 is the center fed dipole with a balun placed between the dipole
and the transmission line. In this case the balun will more than likely only be used to
convert between the balanced connection of the dipole and the unbalanced connection of
the coax. In rare cases, it can also match the 50-ohm impedance of the coax to the 72-
ohm impedance of the dipole. A center fed dipole is inherently balanced, but the type of
center fed dipole shown, where the ends of the dipole are also insulated, can be fed
balanced or unbalanced for the most part.
The second dipole shown in figure 2 is a gamma matched dipole. Notice there are no
longer two separate pieces of conductor. There is only one conductor that is a 1/2
wavelength long. The center of the dipole is connected to the shield of the coax cable:
usually 50-ohm coax. The center conductor of the coax cable is connected to one side of a
variable capacitor. The other side of the variable capacitor is connected to an adjustable
tap that can be moved left and right along one of the two 1/4 wavelength dipole sections.
There are two adjustments here: the variable capacitor and the tap. Both are adjusted
alternatingly back and forth many times to get the best possible SWR at the frequency for
which the dipole has been cut. This is one of the best types of matching systems where a
perfect 1.0 to 1 SWR can be obtained. Usually, the variable capacitor is made up of two
pieces of tubing with an insulating material between them. The smallest tube is adjusted in
and out to adjust the variable capacitor, and the tap which are two clamps, one on the
small tube and one on the dipole are adjusted together for the tap adjustment.
The third dipole shown in figure 2 is the T-match dipole. Here again the dipole is only one
conductor that is a 1/2 wavelength long and the center of the dipole is again connected to
shield of the coax cable. This time there are two taps: one on each 1/4 wavelength section
of the dipole. These taps are adjusted together to obtain the lowest SWR always
maintaining equal distance from the center for both taps. The taps are always moved
together either in towards the center or out away from the center. The center conductor
of the coax that comes from the radio is split going both to the center conductor of the 1/4
wavelength delay line coax cable and to one of the adjustable taps. The other end of the
1/4 wavelength delay line coax cable center conductor connects to the other tap. The
shields of both ends of the delay line piece of coax, the coax coming from the radio, and
the center of the dipole are all connected to together in very close proximity to one
another. This means that the 1/4 wavelength delay line coax is in the form of a loop with
both ends brought closely together.
The fourth dipole shown in figure 2 is the half-folded dipole. This dipole is a single
conductor a 1/2 wavelength long, and the center of the dipole is connected to the shield of
the coax. But this time there is another 1/4 wavelength section that is connected to one
side and folds back to the center. This type of dipole is inherently unbalanced which is
perfect for connecting directly to unbalanced coax cable. The center conductor of the
coax coming from the radio connects directly to the folded back 1/4 wavelength section at
the center of the dipole. This type of dipole has the advantage of connecting directly to
coax without the additional hardware and adjustments of the previous two dipoles:
gamma matched and T matched.
Before ending this first article on antenna basics, the radiation pattern of the dipole will be
discussed. Please refer to figure 3. This is the often seen in the literature donut radiation
pattern of a horizontally polarized dipole antenna. There is a new term: polarized or
polarization which hasn’t been discussed yet. Without going into too much detail, the
polarization of a radio wave is the plane in which the electrostatic field fluctuates with the
signal. So, for a horizontally polarized antenna, and therefore a horizontally polarized radio
wave, the electrostatic field of the radio wave is in the horizontal plane perpendicular to
the direction of motion of the wave. The magnetic field would be in the third plane which is
the vertical plane.
The dark line in Figure 3 is the dipole antenna which is placed horizontally. This is in relation
to the ground. The donut pattern and which is important, represents the directions where
the most intense or strongest part of the radio waves will be radiated from the dipole.
There are still signals radiated in all other directions, but they are weaker signals. So don’t
be confused when seeing this donut in the literature. Saying it again: there are radio waves
radiated in the directions not covered by the donut. The very weakest radio waves radiated
from the dipole are in the two directions out the two ends of the dipole. These signals can
be several tens, hundreds, or even thousands of times weaker than what is radiated in the
direction that is perpendicular to the dipole. In the direction that is perpendicular to the
dipole element, the very strongest radio waves are radiated which is represented by the
largest diameter portion of the donut. A horizontally polarized dipole sitting some distance
greater than 1/4 wavelength above the ground will radiate strongest in two directions. If
the dipole is erected so it’s conductor runs East and West, then it will radiate strongest
North and South. The opposite is true if the conductor runs North and South with the
strongest radiation going to the East and the West. Of course, included in both of these
possibilities is radiation that goes straight up and radiation that goes straight down
towards the ground.
Please refer to figure 4. In this example, the dipole is placed vertically. Again, this is in
relation to the ground. The rules discussed in the paragraph above still apply when it
comes to the directions in relation to the dipole element itself are concerned, but two
things will have changed. First, the polarization of the radio wave has changed. Now the
electrostatic field is fluctuating vertically, and the magnetic field is fluctuating horizontally
which is simple enough. But, the radiation North, East, South, and West changes
dramatically. Now the antenna is radiating in all four directions equally without favoring
two directions at the expense of the other two opposite directions. The antenna is
essentially omni directional. Not omnidirectional in a 3-dimensional sense, but in a 2
dimensional sense which is in a plane that is parallel to the ground.
This leads to the next article in a few months where the discussion will begin with an
improvement to this vertically polarized dipole antenna which is an antenna commonly
referred to as a ground plane antenna. This ground plane antenna is a modification to the
dipole antenna.
Loren Jentz N9ENR.
Trivia
From Last Newsletter: How many Control Operators does the MAARS system have and
do you know who they are?
Answer 7 N9PSN, KA9ZYW, N9FSE, K9ZZZ, N9ASA, KA9WXN & N9LKH
Trivia for next newsletter: Did you know you can use Voice Play Back on the repeater? Do
you know how to use it?
The Workbench
Unfortunately, I don’t have anything prepared at this time. Hopefully, I’ll have some news for
the next newsletter! As some of you may have heard me say on air, I sold one of my FTM 400
XDR radios because I had difficulty pairing it (with the BU-2 Bluetooth chip) with my
motorcycle bluetooth helmet headset. Tom (@ HRO) was kind enough to allow me to come
into the store with my gear to try pairing with the Yaesu FTM 300 to see if the newer radio
worked any better. And, alas, it did! So, my intention was to have this all worked out by now
and be able to report my findings. But life got too busy and while I’ve had the 300 for about
10 days already, it’s still in the box! Once I get it opened and set-up, I’ll use it here in the shack
for a while, then transfer it to the motorcycle. Should be interesting to see what the
differences are. I’m looking forward to making QSO’s via 2 wheels again!
Meetings
There has been some discussion about having a membership meeting now that Covid
restrictions have eased up a bit. More on that as details become available.
Swap Net
MAARS provides a Swap Net every Wednesday night beginning at 9 PM local time.
Thank you for taking the time to read this newsletter about our organization! Please help it along by
asking questions, submitting articles and thoughts so we can all grow together!
KB9JMH@513repeater.org
Board Officers:
President Dave Schank KA9WXN@513repeater.org
Vice President Barry Sprifke W9BLS@513repeater.org
Secretary Jim Westover KB9KBK@513repeater.org
Treasurer Bob Widdish n9psn@513repeater.org
Past President Greg Wolf K9ZZZ@513repeater.org
System Manager Dan Workenaour N9ASA@513repeater.org
Marketing & Communications
Randy Timms KB9JMH@513repeater.org
Control Operators:
Bob Widdish N9PSN
Jim Goelden KA9ZYW
Steve Sundquist N9FSE
Greg Wolff K9ZZZ
Dan Workenaour N9ASA
Dave Schank KA9WXN
Pat Riordan N9LKH
