The Kaw Valley Amateur Radio Club Newsletter
THE TRANSCEIVER
May 2014
Editor: Doug Dunton
www.kvarc.org
ARRL Affiliated Since 1926
2014 Club Officers
President: Paul Mills
Secretary: Susan Sims
Treasurer: Paul Bayless
Antennas and SWR Revisited!
Why revisit this subject again? There have been frequent misunderstandings of this subject.
Where do you tune an antenna? You tune an antenna at the antenna. Tuning is usually done by
changing the length of the antenna. Short antennas are tuned by making them appear longer than
physical length. The most common method of making an antenna look longer is to add a loading coil.
What will the SWR of a resonate antenna be? It will be greater than 1:1, unless we do something to
make it 1:1. A half wave dipole that is ½ wavelength or greater above ground will have an impedance
around 75 ohms. This will give us a SWR of around 1.5:1 If we turn it into an inverted-V the impedance
will approach 50 ohms at some point, thus an SWR of near 1:1. However these changes will change
antenna pattern and takeoff angle. A quarter wave ground plane will be around 25 ohms unless we
angle the radials downward. So, at resonance, a ground plane antenna could have a SWR of as much as
2:1. It is usually desirable to angle the radials downward for best performance and feed line match. Yagi
antennas will have a very low impedance, thus a high SWR unless some matching is done.
Where is the best place to match antenna impedance? The best place to match antenna impedance is
at the antenna or its feed point. Our radios are designed to attach to 50 ohm antennas with 50 ohm
feed line. Therefore the best place to cure these mismatches is at the place where the mismatch occurs.
This becomes more important as SWR increases, and as line loss increases. (See: Understanding SWR by
Example – November 2006 QST page 37)
Why does my SWR increase when I talk? There could be several reasons for an “increase” in SWR as
you talk. First, remember that SWR cannot be read with no power applied to the antenna system. Your
antenna system could have some component that is failing under power. Another could be a “defect” in
your SWR meter, especially those built into radios. Often samples of forward and reverse power are
taken at different times. If a forward sample is taken at a point of low modulation and the reverse
power sample at a point of high modulation, the SWR could be improperly calculated. When this
happens, you may see SWR values jumping around as you talk. Don’t panic, verify.
Why does my external SWR meter read different from the built in meter on my radio? Because you do
not have a perfectly matched antenna system, and the two meters are located at different places in the
system. This leads to myths that antenna feed lines must be a certain length. (There are some antenna
designs where certain feed line lengths should be avoided.) Also meter accuracy varies. Or if you are
using an internal antenna tuner, the SWR really is different at the two points.
I have an SWR on the low end of a band of 1.7:1, high end is 1.8:1, and center of band is 1.4:1. Should I
use an antenna tuner to improve this? No. The tuner will only add to your losses. Your SWR is not high
enough to hurt your radio, so leave well enough alone.
I plan on talking about ESR at the next club meeting. What is ESR? If you really want to know, come to
the meeting. See you there!
Have a wonder filled month. Until next month…
73 de AC0HY
Reminders:
Annual 2014 Membership form at KVARC Application
Ham FAQ: For Hams new to the area or are just licensed - Ham FAQ
•
KVARC Club meeting May 2nd 7:30pm. This will be at the Topeka Shawnee County Library.
Topeka, KS. Eyeball QSO starts about 7pm
•
Regular test session at June 14 at Topeka Library at 1pm. Pre-register with Paul at
ham.test@kvarc.org
•
Regular test session at May 9th at Carbondale City Hall at 7pm. Pre-register with Paul at
ham.test@kvarc.org
•
Tuesday night ARES net on 145.27 at 830pm
•
NEW NET! - Thursday night Carbondale net 800pm on 147.30+ KB0WTH repeater
•
Wednesday night simplex net on 147.440 at 730pm run by KB0WOW –Dan
•
Field day – June 28th and 29th and the 27th if we decide to do some setup on Friday evening.
More details to come
EINSTEIN ON RADIO
"I am often asked how radio works. Well, you see, wire telegraphy is like a very
long cat. You yank his tail in New York and he meows in Los Angeles. Do you
understand this? Now, radio is exactly the same, except that there is no cat."
__Attributed to Albert Einstein
Other info:
Training Topic
What is a Communication Emergency?
One of the primary missions of the Alpha-1 ARES covering Shawnee/Wabaunsee
county, is to provide communications during an emergency. This training
topic will address the question, then, what is a communication emergency?
A communication emergency exists when a critical communication system
failure puts the public at risk. A variety of circumstances can overload
or damage critical day-to-day communication systems. It could be a storm
that knocks down telephone lines or radio towers, a massive increase in the
use of a communication system that causes it to become overloaded, or the
failure of a key component in a system that has widespread consequences.
Most cellular phone systems are designed to handle only about 6-10% of
the subscribers at any one time. This works well in normal situations and
is economical for the company. But when a crisis happens, they quickly
become overloaded as everyone(the other 90%) tries to talk at once.
Examples are easily found. Violent storms and earthquakes can knock down
communication facilities. Critical facilities can also be damaged in
“normal” circumstances: underground cables are dug up, fires occur in
telephone equipment buildings, or a car crash knocks down a key telephone
pole. Hospital or 911 telephone systems can fail. Even when no equipment
fails, a large-scale emergency such as a chemical or nuclear accident can
result in more message traffic than the system was designed to handle.
Some emergency operations occur in areas without any existing communication
systems, such as with backcountry searches or fires. (1)
With such endless possibilities, then, it is important to recognize that we
as amateur radio operators are a valuable resource to the communities we
live in because we possess the skills as emergency communicators, the
equipment and the frequency spectrum to meet the needs of such
communication emergencies. These skills require training and practice.
Training available through ARRL's Licensing, Training and Education
section. We all must be prepared to assist with Emergency Communication in
the event of a disaster.. Why? Because EmComm is a lot more disciplined and
different than general 2 meter communication and Net check-in.
1 American Radio Relay League Amateur Radio Emergency Communications
Course, An Introduction to Emergency Communication, (EC-001), Learning Unit
1, Topic 1: Introduction to Emergency Communication course.
Doug Bluthardt – AC0RS
Please send any equipment you have for sale and I will include in next month’s issue
Elmer-ing
Attached is a form for letting me know what you might be interested in having help with. Or If are
available to help someone. Please fill in as appropriate and email back to me or bring to the club
meeting Friday.
I have mentioned this new item to a few people, I would like to suggest adding a get together some
other time of the month as a learning session. I am open to suggestions as to a day and time. I can try to
schedule time at the library or if a different location is available I would take that as a suggestion also.
So what do you think? Let me know by email or at the club meeting.
ARRL Affiliate since 1926
“Need”/”willing to be” an Elmer Info
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want/need Interests
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Level of expertise (1-5) 1=beginner, 5=expert
Give to Doug(WD0DBS) or email to wd0dbs@arrl.net
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