IW5EDI Simone - Ham-Radio

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160m Antenna - Inverted L

Posted: 08 Dec 2018 01:27 AM PST
http://www.iw5edi.com/ham-radio/2982...nna-inverted-l


Another antenna added from the antenna plan is a 160 meter ¼ wavelength
inverted L.

A 130 foot length of 12 gauge PVC covered stranded wire slopes up from the
ground system to the 40 foot level of the 45 foot tall fiberglass flagpole
(about 60 feet of wire length) and then proceeds about 70 feet toward the
far back edge of my property. The 90 foot start-to-finish dimension just
fits my city lot. At the end, the antenna wire is terminated at about 15
feet above the level of the back yard. The geometry actually resembles an
inverted L that has partially fallen over – in other words, a “lazy L�.
This antenna is used on 160 meters only and is coaxial cable fed.



In place of an active tuner, a 10 turn 4 inch diameter tapped coil wound of
0.250 inch diameter copper wire is used to tune the 1.8 to 2.0 MHz band in
three segments.

Two vacuum relays are used to select the correct amount of the coil for a
particular band segment. No coil turns are added to the top band segment, 7
turns are connected in series for the middle tuning range and the entire
coil is used at the bottom end of the band. All of the base load components
plus the static discharge arrestor are located in a 7 inch square
weatherproof box that is bolted to the ground structure.

The coaxial cable entry point is sealed with silicone sealant to keep the
spiders and moisture out. The wire that brings power to the relays is TV
rotor cable which is rated to be used outside in the weather.



The transient suppressor and coaxial cable braid bus-work is bonded to the
ground system with a heavy braid.



The cross-section of the metal drainage ditch that is used as the ground
system for this antenna is shown below.



This metal drainage ditch is about 100 feet long and runs along the top of
a five foot high concrete block wall that defines the eastern boundary of
my city lot. The drainage ditch measures 12 inches wide and 12 inches deep.
All of the 10 foot long metal sections are electrically bonded together
along the length. This provides a very good earth ground for this 160 meter
1/4 wave inverted L antenna as well as a reflector / ground reference for
the 75/60/40 meter NVIS antenna that is mounted directly above the metal
ditch (see the NVIS page for more details about this antenna).

An improvement that I am considering for the ground system is to add a
couple of wire radials in addition to the drainage ditch ground system.
These radials will be run underground by fishing them through the drainage
pipes buried under my driveway and front lawn. I think Ill connect them
with a remotely controlled relay so that I can more easily quantify their
usefulness during actual on air contacts.

Another improvement under consideration is to add a number of 10 foot long
ground rods along the length of the metal drainage ditch, especially near
to the antenna feed point.

Since my back of the envelope calculations indicate that this antenna is
only about 35% efficient (at best), these combined improvements could
potentially yield as much as another 1 to 2 db of signal strength at the
receiving end of my transmitted signal. Very interesting??



The antenna wire coming from the weatherproof box mounted on the metal
drainage channel (lower center of the photo) first goes up to the top of
the brown painted PVC pole (at the upper right of the photo),



From there it proceeds up to a point about five feet from the top of the 45
foot tall fiberglass flag pole. This places the 160 meter antenna five feet
below and at about 30 degrees crosswise to the OCF Windom antenna wire to
minimize interaction between the two antennas.



The far end of the antenna is attached to t he fence with a pulley and one
gallon paint pail counter weight that takes the sag out of the antenna wire
and allows the antenna pole to sway freely with the wind without stretching
or breaking the antenna wire.



The maximum SWR at the edges of each of the three segments is less than
2.5:1. At 1.945, the frequency that I use the most, the Rs measures 33 ohms
with an Xs of 32 ohms for an SWR of about 1.9:1 according to my MFJ-269
analyzer.

Since the static discharge protection is located at the base of the
antenna, the coaxial feed line goes directly to the shack through a 100
foot length of coaxial cable. The antenna loads nicely and shows virtually
no change in SWR when operating in either dry conditions or on a rainy day.

The antenna handbooks show that the inverted L has a more or less omni
directional pattern that is uniform within about 1.5 db. The signal reports
from any direction using this antenna are always as good as or better than
the signal reports for other hams using top loaded verticals, full wave
loops and dipoles at similar heights. This antenna is not a multi-element
full size vertical array using massive towers, but it does work and works
quite well. This is the one band where I often run the full power in order
to overcome the very noisy band conditions that are typical at the
receiving end.

160 meters is also the band where the 38 inch diameter magnetic loop
antenna (pictured at the left) really shines. This loop often delivers the
best quality receiving signal, especially if there are plasm TVs operating
in the vicinity (see the PIXEL loop page for more details about the
performance of this loop on the 160 meter band).



Article by W6SDO originally available at http://www.w6sdo.com:80/160M.html

The post 160m Antenna Inverted L appeared first on IW5EDI Simone -
Ham-Radio.


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Vertical Dipole Antenna

Posted: 08 Dec 2018 12:47 AM PST
http://www.iw5edi.com/ham-radio/2975...dipole-antenna


VERTICAL DIPOLE

Since I had purchased the Kenwood TS-590 transceiver a few months before I
got my license, I needed an antenna (or antennas) right away for listening
on the ham bands.

The antenna that I put up first was a vertical dipole for 10, 15, 20 and 40
meters. The reasons for this selection as the first antenna to be installed
are that

1. The vertical antenna has many devoted supporters in the ham community
who claim to get fantastic results,

2. The vertical dipole has a very small foot print and requires no radials,

3. This vertical is self-supporting and is very easy to install (except for
the many tuning adjustments that are needed) and,

4. It is almost invisible from the street view in front of the house.



This last reason was considered important for the first antenna as it would
let the neighbors get used to antennas sprouting up on and around the house
without being initially overwhelmed by some visually gigantic structure.

Two Hustler Model 6-BTV antennas were adapted to make up a half wave
vertical dipole by mounting them butt- to-butt on a twelve-foot long 2 by
12 inch wooden mast attached to the deck railing at the rear of the house.

The center feed point of this combination is only about 22 feet above the
ground.

Therefore, I had to eliminate the 75/80 meter sections of the antennas in
order to reduce the total length for each side to about 20 feet.

This vertical dipole configuration was chosen because my house and back
yard layout (a full coverage concrete patio was already installed) do not
lend themselves to the installations of a good ground radial system.

One great feature of the way that this antenna is mounted is that the
dipole can be rotated to horizontal and the ends can even be swapped –
which makes it very easy to reach any of the tuning traps from ground level
or from the deck to which it is mounted! In addition, I have heard some
hams say that with an incline angle of 45 degrees the signals come in
earlier and leave later as the bands open and close – easy to check out
with this setup.

The vertical dipole is fed at the center by a 1:1 balun and is further
isolated with a 14 turn coil of RG-8 coaxial cable wrapped around a 7 inch
diameter fiberglass form. The coaxial cable is routed at 90 degrees away
for the antenna for about 20 feet before it runs across the roof of the
house and then finally drops down to a 10 foot long ground stake. Here the
coaxial cable passes though an Alpha-Delta 2 KW surge protector with the
braid is connected to ground. Next, a 50 foot length of coaxial cable runs
up the second floor shack.
The Dipole in Horizontal position

This antenna has been found to load great with SWR values of under 2.5:1
over the entire span of the bands that it covers.

A limitation of this antenna was the lack of coverage on the 75/80 and 160
meter bands. This deficiency was quickly and easily remedied by the
addition of a Pixel Technologies Magnetic Loop Model PRO-1B all band
“listening only� loop antenna.

I have recently made some back of the envelope calculations estimating the
performance of this antenna.

The takeoff angle for this antenna should be around 15 degrees for 10
meters and between 25 and 30 degrees at 40 meters. The radiation efficiency
should be equal to or slightly better than the typical 1/4 wave vertical
antenna with 4 to 8 radials.

Note that due to the 1.25 inch diameter of the aluminum tubing that makes
up the elements, the length of each segment of this vertical is about 5%
shorter than it would be for a 12 gauge wire antenna. Due to the tuning
traps for each of the bands, the physical length of this dipole, compared
to a full length dipole, is 99% when it is used at 10 meters, 94% for 15
meters, 83% for 20 meters and 65% for 40 meters.

Taking into account the losses that are associated with the 150 feet of
coaxial feed line, the balun that feeds the antenna, the traps and the
overall antenna length for each band (listed above), the loss of power for
the total antenna system can be estimated. The total power loss is around
1.5 db on 10 meters, 2 db on 15 meters, 2.5 to 3 db on 20 meters and maybe
as much as 4 to 5 db on 40 meters when compared to a full length vertical
dipole with a short feed line and a core type current balancing choke. If
your signal is 10db over S9 at the receiving location, these losses will
hardly matter.

Choosing one of the trap free antenna designs that are now available, in
place of the Hustler design, could minimize the losses on the 20 and 40
meter bands.

Finally, now that all of the antennas in the plan have been installed the
listening results for this antenna can be compared with my other antennas.

So far, some preliminary comparisons have been made on the 17 meter band.

The antennas that I can now select include a hex beam, an inverted V off
center feed Windom (a long wire at this frequency) with good
omni-directional characteristics due to the inverted V construction), my
vertical dipole to which I have added the 17 meter band and a two
wavelength horizontal loop antenna. Each has its own advantages and
disadvantages and the shoot out between them has been very interesting. The
four antennas can be set up to use the four antenna selector switch buttons
on the front of the Alpha amplifier which makes A-B-C-D testing very easy
and a lot of fun!

The preliminary 17 meter observations a

1. The hex beam is always the most quiet and has the strongest signal in
both transmit and receive mode even though it is only 24 feet above the
ground.

2. The loop has an equally quiet noise level but delivers signal strengths
that are about 6 db less than the hex beam.

3. The OCF inverted V has a noise level that is 2 to 3 db higher than the
hex beam and produces signal levels that are between equal and 4 db lower.

4. The vertical dipole usually has a 3 to 6 db higher noise level, compared
to the hex beam, and produces signal levels that are typically 3 to 6 db
less than the hex beam. It does much better on transmitting than it does on
receiving due to the high noise level when it is used as the receiving
antenna.

Article by W6SDO orignally available at http://www.w6sdo.com/VERTICAL.html

The post Vertical Dipole Antenna appeared first on IW5EDI Simone -
Ham-Radio.