QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/files/races/tecantn.txt

Text File | 1994-11-27 | 15KB | 273 lines

Page 1

              TECAntn   Version 1. 3     3/1/92



Subject: TECHNICAL [CATEGORY: TEC]      ANTENNAS

ANTENNAS & SLINGSHOTS
Most of us have had the experience of putting up a portable
antenna in a remote area -- most often for Field Day. My most
memorable time was on a deer hunting trip. I climbed a small pine
tree to put up a random wire. I then spent an hour trying to get
the pitch off me and my clothes.
Since that time I have used several other methods that don't
require one to get so personal with the supports. I tried tying a
rock to the end of a rope with the intention of throwing it over
a low branch. The rock kept coming off the rope and I succeeded
in knocking a dead branch off the tree. I settled for a lower
branch and had to worry about tall campers running under it.

I saw an article where someone used a bow and arrow to put up an
antenna and I decided to give it a try. I used my archery fish
reel on the bow with some Dacron line. It worked very well; I was
able to put up a 137-foot random wire that turned out to be
vertical. The best tree for the antenna was a tall pine about 20
feet in back of my camper. I was glad that I used an arrow with a
blunt head when it came back down on top of my camper, which was
too close for comfort.
In archery, the rear sight of the bow is called the anchor point.
It is on your face, cheek, corner of your mouth or etc., where
you place your fingers of the hand that you use to draw the
string. When putting up the antenna, unless it's a very tall
antenna, you will not need a full draw. Another ham was erecting
his first antenna using a bow and arrow for Field Day a few years
ago and used a full draw. The arrow shot up over the tree and
headed for parts unknown. He never found the arrow but did find
the string on the opposite side of the tree and was able to get
the antenna up. (
Another method I have used that works well is the use of a
slingshot and "Jetline". Jetline is used by utility companies and
others for putting up power lines and such. It lends itself to
antenna work very nicely. It comes in a plastic tube. I hold the
tube in the same hand that I hold the slingshot, with the open
end of the tube in the direction the fishing sinker is to be
propelled. Slingshots are great for pulling the Jetline from the
tube and carry the weight up and over whatever you want to use as
your aerial support. A 2-1/2 or 3 ounce weight is used to provide
enough weight to get your Jetline over a rough branch surface and
back down to where you can reach it. I haven't figured out a way
to get the Jetline back into the tube. There is enough in one
tube to put up several antennas -- depending upon the height, of
course.
Fishing reels with monofilament line have also been used with
good results.
Before Amateur Radio antennas were installed on Sacramento's new
Blood Bank building, we needed to put up an antenna in a hurry to
fulfill our obligation in an upcoming Simulated Emergency Test.
The garage of the building has a 40-foot ceiling with exposed
rafters and stringers. I used the slingshot to put up a forty
meter dipole inside the garage. It was successful, the radio
worked fine, and the Blood Bank officials were very impressed.
The slingshot and Jetline was used during the forest fires to put
a 2-Meter "J" antenna 40 feet up a pine tree at a fire camp.
I find the slingshot and fishing sinker easier to use and pack in
the trunk of a car than the bow and arrow. The slingshot I use
and prefer is a folding Wrist-Rocket. It also makes a usable
survival weapon. I used it in a park to put up an antenna; I
don't believe it appears as threatening as a bow an arrow to
other park users.
Both methods make a difficult job both easy and fun, a slingshot
is cheaper than pole climbing spurs, and keeps you and others
from getting emotional about a pine tree. LES BALLINGER. WA6EQQ @
WA6NWE.CA.USA State RACES Headquarters Station Manager Governor's
Office of Emergency Services.    RB082 to 086

HIGH FREQUENCY ANTENNA SURVIVAL TIP
The following was submitted to us by Patricia Gibbons, WA6UBE,
City of San Jose Communications:
"I made a trip to Berkeley to visit the shop manager for a
facility run by Mackay Radio -- they maintain marine
communications gear on the larger craft operated by American and
foreign shipping lines. I wanted to get the correct part numbers
to make up a wire antenna for our EOC just like those on board
ship that go between the masts, complete with what are called
'safety links'. These are special sections of wire that are
weaker then the antenna line itself and has a heavier, longer
wire in parallel with the weaker wire. The purpose on a ship is
to allow the weak link to break in a heavy storm. This allows
additional slack in the antenna wire so that the entire antenna
will survive instead of it all coming down. This concept is ideal
for our communications center because we have two large monopoles
to support the various microwave and various VHF/UHF antennas for
our city government frequencies. So if this High Frequency wire
antenna will go between the two poles, and if they sway a lot in
en earthquake, the weak lines will break instead of the entire
antenna system and thereby survive when it will be needed the
most!!!"
RB151.

NVIS ANTENNAS
There has been what can be called more than somewhat mild
excitement in Northern California emergency communications
circles over a form of high frequency radio propagation. It's not
new, but I venture to say that very few have used and understood
it. "It" is called NVIS -- Near Vertical Incident Skywave.
Patricia Gibbons, WA6UBE, presented a paper on NVIS at the 1990
Pacific Division ARRL convention in San Jose. It caused quite a
stir. She quickly ran out of handouts and has since received
dozens of requests for more. The handouts included reprints of
articles from military communications magazines reporting the
results of many tests.
Near vertical incident skywave means forcing your radio signals
to travel straight up (i.e., 80-90 degrees) and back down. This
achieves radio coverage in circle having a radius of 300 miles
and more. Stop and think about that for a moment. Complete
coverage within such a circle on frequencies between 2 and 10 or
12 Megahertz.
Some readers may wonder what's so good about this. So now is a
good spot to say that if only DX (long distance) is your thing,
skip on and read one of the other fine articles in this
publication. We are talking about dependable local area high
frequency communications -- the type we need for tactical public
safety communications in the Radio Amateur Civil Emergency
Service, the Civil Air Patrol, SECURE, search and rescue,
forestry, pipeline and similar services. In tactical
communications we don't want DX.
How frustrating it was in years gone by to drive away from, say,
a 4585 KHz base station, only to lose a good 400 watt signal a
mile from the transmitter! All the while receiving, loud and
clear, a 50 watt transmitter some 200 miles away. Very
frustrating. We really didn't know why. When VHF-FM radios and
repeaters came along, most of us retired HF mobile radios for
tactical communications.
The reasons we haven't enjoyed good HF tactical communications,
whether AM or SSB, have been the base and mobile antennas. The
classic dipoles, a quarter to a half wave up in the air. The
mobile antennas, designed for use by Amateur Radio operators,
have the same general propagation characteristics -- low take off
angle for DX.
Virtually every Amateur Radio mobile HF antenna is unsuitable for
day-to-day tactical communications. They are variously bulky,
mechanically weak, won't survive continual whacks from limbs and
low overheads, look like Neptune's trident or a misshapen coat
rack. They may be fine for hobby communications but not for
tactical public safety use. In that type of service we want one,
simple antenna that is permanently installed and we don't have to
think about or fuss with again.
So how do we achieve NVIS? By getting those sky hooks down near
the ground. Let's start with the base station antenna.
Horizontal, of course. Dipole or long wire. Place the antenna as
low as two feet above the ground but no higher than about thirty
feet without a counterpoise. Use an appropriate and sturdy
antenna tuner; you will use the one antenna for all frequencies
between 2-12 MHz.
A longwire antenna is suitable in field setups but not
recommended on office buildings or other urban environments. The
reason is that unbalanced antennas frequently create interference
problems with telephones and other communications and electronic
equipment. These problems are substantially reduced or eliminated
with a balanced antenna system.
The antenna tuner of preference is one that is automatic. Such
tuners are available now that do not require any control cables;
they require only the coaxial transmission line from the
transceiver and a 12 volt DC cable. The tuner is placed at the
far end of the coaxial cable. There are then two basic options: a
longwire or a balanced (dipole) antenna. The longwire can be any
length -- the longer the better to approach the lowest operating
frequency. A very good ground connection is necessary and often
quite difficult to obtain on a rooftop. (When we are talking
about running ground connections we mean the shortest possible
runs of 2 to 3 inch copper strap -- never wire or braid.) For a
balanced antenna, you can place a 4:1 balun on the output of the
antenna tuner, thence to a 450 ohm feedline to the dipole
antenna. Any NVIS antenna can be enhanced with a ground along the
surface that is 5% longer than the antenna and separated by .15
wavelength at the lowest frequency to be used.
For the HF-SSB mobile radio, a sixteen-foot whip is probably the
best. Such a whip may be both costly and difficult to find. For
NVIS, the antenna is used folded down, both in motion and at
rest. That's right, it is not released to go vertical. Most us
use the heavy duty ball joint mount, heavy duty spring, and
readily available 106 inch whip.
To further improve the NVIS propagation at rest, the mobile whip
is adjusted to go parallel to the ground and away from the
vehicle. A further enhancement is to remove the whip and run out
a longwire 30, 50, 100 feet long. Patricia Gibbons carries orange
traffic cones, about 18 inches tall, and notched at the top to
lay the antenna wire away from the vehicle.
The Russian military have been using NVIS antennas on their
vehicles for quite some time. They appear to be about 4 meters
long and about six inches above the top surface of the vehicle.
At least one American manufacturer makes an NVIS antenna for both
military and civilian vehicles. On a van it looks no more
obtrusive than a luggage rack.
The automatic antenna tuner is located in the rear of the vehicle
and as close as possible to the mobile antenna feedpoint.
An HF-SSB mobile radio was recently installed in one of our State
Office of Emergency Services trucks. The installer and the
vehicle were 80 airline miles away and the time was about 2 p.m.
In the State SECURE (State Emergency Capability Using Radio
Effectively) system this calls for using a 7 MHz channel. We
established contact; the mobile signal was received here in
Sacramento at about S5 to S6. I then asked him to loosen the ball
mount, flop the antenna down horizontal and away from the truck.
I could tell by the pause and tone of his voice that he thought I
had lost it. When he returned to the air his signal jumped to S9.
By the same token he thought I had cut in a linear amplifier
because of the improvement to my signal. I assured him that the
improvement was due solely to his flopping his antenna
horizontal.
You need not be concerned over the orientation of an NVIS
antenna; it is omnidirectional.

Every Monday night from 7-8 p.m. we conduct a State RACES net on
3545.5 kHz using AMTOR. One night the net was concluded and
secured. While the hams were cleaning up one of them noticed that
we were being called; there it was on the screen. But it belied
the loudspeaker; there were no discernible AMTOR signals -- only
a high noise level. Yet, there was that station, WA6UBE, calling
us at W6HIR. Yes, it was Patricia Gibbons proving an NVIS point
again! She was transmitting to us from 82 miles away with an
antenna lying on the ground along her driveway and using 3 watts
of power!
On another statewide evening RACES net, our Monday night 8 p.m.
3952 kHz voice net, Bill Pennington (WA6SLA) compared two
antennas. One was a vertical and the other was a horizontal quite
close to the ground. His observations were interesting and
typical of NVIS propagation. Almost all of the signals received
on the vertical were higher in voltage than the NVIS antenna but,
be that as it may, the signal to noise ratio is superior with the
NVIS antenna. The noise floor is measurably lower on the lower
antenna, thereby providing better overall communications.
I heard more than one Amateur say, after listening to Gibbons'
NVIS presentation and subsequent demonstrations, decide to jump
back into HF-SSB mobile radio again. These people, like I, are
interested primarily in the mobile tactical public safety
communication applications.
There is an easy method to improve the NVIS radiation of your
dipole antenna. Let the feedpoint sag five to ten feet below the
horizontal. This will alter the radiation to improve the vertical
angle to achieve an approximate 2 dB improvement at no cost.
Many are excited about an old but little understood and practiced
means of HF radiation. If you need it, try it. You'll like it.
RB152-156

ANTENNA SAFETY
Use extreme care when raising or elevating antennas for the first
time. Be sure you can see any overhead or nearby power lines that
are within the fall radius of your antenna. Last month a
television station technician raised his telescopic 40-ft mobile
antenna into unseen overhead powerlines. The resulting short
circuit threw him clear and set his van of fire. He regained
consciousness, attempted to get the fire extinguisher from the
burning van, and was electrocuted. RB 86.

LOG PERIODIC AT OES
A high frequency log periodic antenna was installed at OES
headquarters in Sacramento by the efforts of 11 hams, two
commercial sky hook crane operators, three Sacramento
firefighters with a 150-foot snorkel and 6 State employees. The
hams assembled the KLM 40-through-10 meter log periodic on the
ground and awaited less windy weather before it was hoisted atop
a 75-foot tower. A special thanks to these hams for a job well
done: Les Ballinger WA6EQQ, Herb Bennett KA6VHF, Jim Buckman
N6HOS, Bob Cloud W6CFQ, Keith Crandall K6QIF, Marion Henson
W6NKR, Herb Hildebrand W6UBI, Chris Huber N6ICW, Norm Nelson
KA6YRC, and Jim Pratt N6IG. The antenna is connected to a Kenwood
930S HF radio at the State OES Headquarters RACES radio station
W6HIR. Sgd/Stan Harter, KH6GBX, State RACES Coordinator 87-5