Amateur Radio
Amateur Radio has been a
wonderful hobby for me for many years! I especially
enjoy the opportunity to build meaningful friendships with other
hams.
I became a licensed ham in 1972
to facilitate telephone patch calls to my wife Pat from aboard ship
in the Pacific during my 28 year Navy career. I was
fortunate to operate my own equipment (Kenwood TS-520 and trap
vertical) from five Navy ships.
Station layout
The new Heil PR35 dynamic microphone was recently added to the
station. You can read a review and comparison of this
microphone and others by clicking
microphone review.
Kenwood TS-870
with matching SP- 31 matching speaker and PS-52 power supply (not
shown)
Palstar AT1500BAL balanced line antenna tuner
Ameritron AL-80B linear
amplifier.
The antenna
10 - 160 meter tuned
horizontal loop antenna fed with 450 ohm ladder line all the way
into the ham shack to an Palstar AT1500BAL balanced line antenna tuner.
.
The above graphic depicts
the overall layout of the delta shaped horizontal loop antenna consisting of
546 ft. of #16 "silky" stranded wire cut to one
wavelength long on the lowest operating frequency (160 meters).
Note: Click
80 meter loop
for a sketch of a similarly constructed 10 - 80 meter horizontal loop
that was previously in operation.
A
- Method used to bring 450 ohm feed line into the shack
consisting of a painted 1 x 6 board cut to the window's width.
The feed line passes through a slot. Clear silicon sealant was used
throughout.
B -
One of three corner loop suspension points consisting of nylon
pulley attached to dacron halyard.
C -
Loop antenna feed point.
'Silky' 16 AWG, 19 strand, tinned, 40% copper-clad steel forms the
loop itself and 450
ohm, 16 AWG, 19 strand copper-clad steel conductors, poly-clad
'window' is used as the feed line.
Why choose a loop antenna?
Loops are usually cut a full
wavelength long on the lowest expected operating frequency. The
formula for a full wave loop antenna is Length (feet) =
1005/f MHz. For example, a loop for the frequency of 3.800 MHz would
be calculated as follows: 1005/3.8 = 264 feet.
A multi-band loop antenna offers
significant advantages especially for hams who prefer to only use one wire
antenna for all bands:
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A loop is quite forgiving and
perfect symmetry is not essential. Ideally the loop should be be in
a configuration providing the greatest enclosed area at the
highest height possible. Since the loop can be erected in unusual
places and still perform well, treetop suspension is often used. I
rely on heavy duty nylon or black dacron halyards with nylon pulleys
at each attachment point to keep equal
strain on each leg of the loop. A slingshot, fishing line and
heavy sinker get the halyards
up and over the trees as necessary.
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Unlike a center fed dipole, the loop can be fed at any convenient point.
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Since the design of a loop is
typically a square or delta form, the need for a long straight
run of wire such as a dipole is diminished.
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A loop makes for an efficient broadband
radiator, even when low to the ground or close to obstructions such
as tree limbs. The majority of the amateur bands are
harmonically related, typically the 1st harmonic. A loop is
easily tuned to resonance on all harmonics of its fundamental
frequency. A dipole by contrast is easily tuned to resonance only on
its odd harmonics. A loop starts out with 1.2 dB of gain over a
dipole on its fundamental frequency.
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A loop's gain over
a resonant dipole increases with the increasing frequency of
operation. Therefore, when used on its harmonics, a loop's signal advantage
over a dipole likewise increases. At higher bands, radiation angle
is lowered resulting in improved DX performance.
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The venerable loop is easy for
a balanced line capable tuner to match on all bands when fed with
300 or 450 ohm balanced feed lines.
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Although I'm not convinced,
most hams who use loops often claim that a loop is less
susceptible to atmospheric and man-made noise.
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Ladder line fed loops
significantly reduce the chances of rfi in the shack.
The antenna does not rely on the need for a good RF ground to
the same extent as unbalanced coax fed dipoles or loops.
There is widespread misconception on this point. More
about this below...
Many hams find it
difficult to bring ladder line all the way into the shack to the
tuner and resort to the use of remotely located coax fed balun
(usually 4:1)
connected to the ladder line. I have tried this
approach and found that it usually works better on some bands than
others. My recommendation is to avoid this technique if at
all possible. Finally, try to use a tuner design that has
been optimized for this type of antenna.
You too may want to consider the
time-honored loop. It is simple and inexpensive to homebrew and can
yield surprisingly effective performance. All things
considered, it's a great multi-band antenna.
visit
http://www.cebik.com
for a theoretical examination of the effectiveness of large loop
antennas.
Why feed the loop with balanced line?
If you doubt the viability of
feeding wire antennas like loops and dipoles with open wire line,
read the following explanation courtesy of K5UA "Charles":
There are two kinds of line loss, the matched line loss and the
mismatch line loss.
Matched line loss is measured at different frequencies in db per 100
feet when the line is terminated into a load which is identical to
the characteristic impedance of the line. The loss increases
as the frequency increases.
Mismatched line loss is an additional attenuation of the signal
because of the line being terminated into a load which is
different than the characteristic impedance of the line. This
loss increases with frequency, but it also increases with the
magnitude of the mismatch. Needless to say, lossy lines like
the small coax have higher mismatched line loss numbers for the same
amount of mismatch than the lower loss, large coax lines.
Matched line loss is unavoidable, but mismatched line loss is
avoidable if the load can be matched to the line at the load end of
the line. An example of this would be a gamma match at the
yagi terminals to transform the 16 ohm impedance of the antenna to
the 50 ohm characteristic impedance of the coax. Another
example would be to use a 4:1 Balun at the antenna terminals to
bring the 16 ohms closer to 50 ohms.
The match can also occur at the transmitter end of the line, but the
mismatched line loss would be there. The transmitter would be
happy looking into a 50 ohm load, but the mismatched line loss would
still be present because the load is not matched.
The beauty of open wire line is that the matched line loss is
virtually zero. Even with large line/load mismatches, like
10:1 or 15:1, the additional mismatched line loss is very low.
As long as the user has a conjugate match on the transmitter end of
line using an antenna matching network, virtually ALL power is
radiated by the antenna. Power can not disappear, it is either
radiated or lost in the line by attenuation of the dielectric
material between the transmission line wires. This is why a
random wire of reasonable length may actually radiate MORE power
when fed
by open-wire line through a tuner, than a perfectly matched
half-wave dipole fed with small coax, assuming the feed line length
of each is over 100 feet.
The net effect of this is that you can put up a random length dipole
(or a loop as discussed here) and use it on all bands with very
little line loss and not have to worry about a bunch or resonant
dipoles interfering with each other.
K5UA, in another email, goes on
to say:
Take a look at this article
at
http://lists.contesting.com/archives/html/Towertalk/1999-06/msg00184.html from a Belden Wire
employee about the history of coax and why does 50 ohm cable exist:
Speaking of 50 ohms, the probability that
any single element antenna
is going to have a feed point impedance of 50 +/- j0 ohms is
virtually ZERO.
Likewise, when I hear of someone bragging about their quad or yagi
that is 50 ohms at resonance, I always ask them how much gain and
front to back did they have to sacrifice to get that 50 ohm feed
point impedance. Apparently when God was designing the
universe and the laws of physics, he did not realize that the tail
(50 ohm coax) was going to wag the dog
(gain/front-to-back/multi-band operation) in the antenna world.
The concept of resonance also appear to baffle most amateurs because
they do not know or understand the three components of impedance
(resistance, inductive reactance, and capacitive reactance). A
lot of amateurs believe that resonance occurs only when the antenna
impedance has the same 50 ohm resistive component as the coax
impedance. Actually, resonance is simply defined as the
absence of the reactive component of impedance, or in other words, a
purely resistive load. If the impedance of a resonant dipole
is 80 ohms and you're using 50 ohm coax, the best SWR you can
achieve is 1.6 to 1.
SWR really messes with the ham mind, especially with beam antennas
where the SWR curve is hardly ever centered on the resonant
frequency of the antenna because the feedpoint impedance at
resonance is rarely 50 ohms. The SWR curve is therefore skewed
to one side or the other of resonance and non-symmetrical. The
worse the mismatch of the coax and the antenna at resonance, the
greater the skewing effect and asymmetry of the
SWR curve.
Note: Visit
www.k5ua.com
for details of his 40 meter two element phased array.
Click
other photos
for additional Amateur radio photographs of interest.
 Links
to other Ham Radio related papers authored by KG9OM
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Being a good "Elmer" (Amateur Radio
mentor) involves much more than assisting someone to pass the
license examination. I've always been eager to do my part to
welcome new operators to the HF bands. Most new hams
develop their operating practices--most good, but some not so
good--simply by listening to more-experienced hams. I like
to urge them to learn
Good Operating Practices . << Click this link
to read my suggested guidelines based on what I've learned from
listening to other hams since 1972. My philosophy is that
amateurs who develop good operating practices will help sustain
Amateur Radio's "long and proud tradition of self-regulation."
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Click
>> Electric Radio... Alive and
well to view a PowerPoint presentation KG9OM
provided to the Murray State University Amateur Radio club
02/03/04. This presentation examines why and how to restore
vintage ham radio equipment.
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Click
>> Enhanced SSB Audio to
view a PowerPoint presentation KG9OM provided to the Murray
State University Amateur Radio club 10/07/03.
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Click
>>Boat Anchor Radio Restoration
Project
which showcases KG9OM's restoration of a vintage Johnson Viking
Valiant 10-160 meter AM/CW transmitter, Hammarlund SP-600
receiver and Heathkit Marauder transmitter.
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Microphone reviews:
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