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1994-11-27
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215 lines
IMMMMMMMMMMMMMMMMMMMMMMMMMM;
:[210 012[:
:[210Condo Communicator012[:
:[210 012[:
HMMMMMMMMMMMMMMMMMMMMMMMMMM<
Subject: Condo Communications
Welcome to the fifth exciting, thrill-packed issue of Condo
Communicator, a newsletter devoted to those amateurs who, for various
reasons, must configure their stations to operate from restrictive
areas such as condos, apartments, townhouses, neighborhoods with
outdoor antenna restrictions, ships/boats, mobile homes, or wherever
they fry their burgers and call QTH.
TABLE OF CONTENTS PAGE
Soapbox............................................... 1
Art, N0OQS
Technical .......................................... 2
Dave, W8NF
Station Descriptions ............................... 3
Dave, W8NF; Howard, N9RUI
SOAPBOX
Whilst struggling to get a little homebrewed transmitter to work, I
gave some thought to the concept of matching. Just as it's important
to match the impedance between different circuit components to
maximize the transfer of power, it's important to have a good match
between your ham radio activities and station requirements in order to
maximize the pleasure you can derive from the hobby.
For example, if you enjoy providing telephone patches between overseas
military personnel and their families stateside, you'll derive
considerable pleasure from smoothing the radio links for troublefree
communications. It certainly is no waste of money to purchase the
best equipment available, including beam antennas, high and sturdy
towers, and amplifiers to overcome any obstacles placed in your path
by mother nature. In this case, there is a good match between the
activity and the station, maximizing the pleasure derived.
But if you live in an apartment, you're going to face considerable
frustration pursuing the same activity. Even with sensitive receiving
apparatus and an amplifer, you'll not provide the same quality of
communications as often as the fellow with the space for large
antennas. The families you're trying to help will not be happy with
the scratchy and fading signals. In addition, your neighbors will
certainly not appreciate the RF overload into their televisions and
other appliances, and they will quickly let you know of their
displeasure. Given such a mismatch between the activity and the
station, you'll not derive much pleasure.
On the other hand, if you enjoy just trying to get a signal out of a
"covert" location, then living in that same apartment could provide a
Condo Communicator #5 Page 1
great deal of fun indeed. Imagine the jollies I got when receiving a
QSL card from a station I worked in Finland on 20 meters with less
than a watt into an attic wire loop. Or the fun of building a small
transmitter and getting it on the air, with no RFI and good, solid
contacts. (So what if I had to seek troubleshooting advice from all
my friends and loads of folks on Internet and packet?) The point is,
there's a good match between my activities and station capabilities
given the set of environmental restrictions within which I choose to
live.
If you find operating from restrictive space frustrating, you may want
to try reconciling your operations with your circumstances. If you
want to run overseas phone patches from your apartment, you can fight
the unit's management to install a tower, fight your neighbors so you
can run high power, make a scientific breakthrough in the science of
wave propagation, move, abandon the hobby, or you can examine what
you're doing to see if you can make any modifications to produce a
better match with your station and operating restrictions.
TECHNICAL ADVICE
Dave, W8NF of Denver, Colorado, offers some advice about radio
frequency interference. I had mentioned RFI problems with an old DX-
20 transmitter. Connected to a dummy load, and sitting on top of the
family TV, the DX-20 produces zero interference. But, just hook it up
to the attic antenna and the TV picture gets wiped out, worst on
channel 2 but bad enough on all the others.
Dave says:
1. Reduce RF currents on the coax. Wind the coax at the feedpoint to
the antenna into a coil, about 5 or 6 turns at 6 to 8 inches
diameter.
2. The signal from the antenna is probably coupling into the AC power
lines, and from there it's saturating the TV tuner. Filter the
TV's AC line. As the first element, use some series impedance,
like a ferrite bead or coil.
I wonder what would be a good ferrite composition to use and if
anything of the appropriate mix is sold that will just clamp over the
AC cord. I've had no luck with the variety sold by Radio Shack.
Anyway, for those of you having similar problems, give Dave's
suggestions a try.
Some more technical advice from Dave regarding limited space antennas,
who suggests using the G5RV design. As radiation from a wire antenna
occurs at high current points, then it's important to get the middle
of a center-fed antenna (the high-current point) as high as possible,
and it's less important to get the ends as high. Neither is resonance
as important as getting as much current as possible into the wire. If
you're not overly concerned about directivity or radiation angle, and
if you can match the thing, then you're getting current into it, and
it'll emit a signal.
The G5RV antenna is essentially a configuration of wire that shows an
SWR of less than 5:1 on all bands when no tuner is used. The G5RV is
a center-fed, 102-foot wire. You feed it with ladder line that's
Condo Communicator #5 Page 2
about 30 feet long (or 1/2 a wavelength at 20 meters). Now you have
an antenna that's 3/2 wavelength of 20 meters and resonant on that
band. Then, to the ladder line, attach your coax, first making a
coaxial balun composed of 5 to 6 turns at about 6 to 8 inches in
diameter. This produces an impedance at the transmitter side of the
coax that most tuners can match from 80 through 10 meters.
If, like me, you don't have enough room in your attic for 102 feet of
wire, even snarled, then Dave suggests cutting everything by half for
an antenna you can match from 40 meters through 10 (with a tuner).
That means a 51-foot length of wire, center fed, with the open wire
feeder cut for about 15 feet (a half wavelength on 10 meters).
STATION DESCRIPTIONS
While we're on the topic, Dave will be using the G5RV design at his
new house where the attic is larger. Currently, Dave lives in a house
with two attics. His station is:
1. Tiny attic: 6/10/15 meter dipole. Also works on 12 and 10
meters. No tuner. 10 watts. No RFI.
2. Larger attic: 40-meter dipole, with center point as high as
possible and the ends "bent, twisted and gnarled in
whatever shape needed to get the thing to fit."
Tuner used. Won't match on 80 or 20, but operates
on 40, somewhat on 15.
When Dave fires up the SB-220 amp, however, his garage door goes up
and down!
As you know, I've asked folks who live in buildings higher than two
stories to send in their station descriptions. While no one living in
on the 20th floor of an apartment has sent in anything yet, Howard
Miller, N9RUI of Skokie, IL, near Chicago, has sent in a description
of his third-floor setup.
Howard uses an inverted vertical. It's made of thin magnet wire and
is 35 feet long. With a small stone weight on one end, it's lowered
from the window and blends in nicely with the brickwork on the side of
the building and can't be seen. Howard has taped two counterpoise
wires in opposite directions to the inside wall near the floor of his
apartment. With this setup and a one-watt HW-8 Heathkit rig, Howard
has worked into Indiana on 40 meters.
Howard's inverted vertical works fine from his third-story perch. I
wonder how height affects the signal pattern of a vertical. Is the
low-angle radiation of a vertical enhanced by being elevated?
Although the building would block a good part of the signal, would an
inverted vertical hanging from the 40th floor of a high-rise radiate
as well in the free-space direction as an inverted vertical nearer to
the ground? And what does inverting the vertical do to the signal
pattern? Some of you antenna wizards write in and let us know. You
could be helping a high-rise ham.
The newsletter is pretty short this month. After all, it's only as
long as you make it. So, if you'd like more station descriptions and
less editorializing from me, then send your notes, ideas, station
description, war stories, editorials, and so on to me at:
Condo Communicator #5 Page 3
CompuServe: 72064,374
Internet: awinterb@du.edu
Packet: n0oqs @ w0ljf.#neco.co.usa
US Snail: Art Winterbauer
10047 E. Mexico Ave.
Denver, CO 80231
Also, listen for snippets of this newsletter on Hap Holly's (KC9RP)
Radio Amateur Information Network (RAIN), heard on various nets or by
direct dialup (708-299-INFO, no charge except for long-distance
costs).
73,72. Art.