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 Previous: Amateur Radio Antenna Bill in Play in Vermont |  Next: It's Musical Chairs Again for Next ISS Crews |
By Anthony A. Luscre, K8ZT
Contributing Editor
February 5, 2004
When the sunspots and thermometer drop, it's time to explore the low bands. You might be surprised how well QRP can work there. This time, we explore antennas and equipment for 160 through 30 meters.
Antennas
There's good news and bad news concerning low-band antennas. (As always) first the bad news: Because of the size that would be required, traditional gain antennas such as Yagis and quads are rare on the low bands, although even rotary beams are not unheard of. While even a "compromise" two-element Yagi for 160 meters would be pretty unwieldy (let's not even consider the "ice storm factor" here), 80, 40 and 30 meter beams are much more feasible. For example, the Cushcraft 40-2CD 40-meter Yagis (there are two) at W1AW have elements in the vicinity of 40 feet, spaced approximately 21 feet apart. A full size, three-element 40-meter Yagi can provide more gain, but it would have to be substantially larger. Steve Babcock, VE6WZ, describes a practical two-element short-boom Yagi for both 80 and 40 on his Web site.
Now the good news: Simple homebrew wire antennas such as dipoles, doublets, Zepps and even wire arrays (more on wire antennas in a bit) can expand your chances of making more contacts on the low bands, even at QRP power levels. For hams with no space or support to hang wire antennas, vertical antennas can provide low-band capability for QRPers.
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Before we get started, gather your antenna books. Here are a few suggestions for antenna books: The ARRL Antenna Book, The ARRL Antenna Compendium (20th edition) (there are other editions in this series) and Low Band DXing by John Devoldere, ON4UN. You also may want to visit the "Antennas Links" page of my Web site.
Wire Antennas
When someone says "wire antenna," most hams
immediately think "dipole," but there
is a wide variety of wire antenna types. My favorite Field Day antenna is an
88-foot doublet fed with
low-loss, low cost 450-ohm "ladder line." Other common wire antennas for
low-band operation include the Zepp, the G5RV, the terminated, tilted
folded dipole (T2FD),
the sloper, the loop, the inverted V, the bobtail curtain, the Windom, and whatever else your
imagination can come up with.
 The 80/40-meter rotary Yagi at VE6WZ. [VE6WZ Photo] |
A rotary beam for 160 meters might be out of the question, but it's not impossible--given sufficient real estate and available support structures--to erect a wire beam for 160 meters or 80 meters at relatively low cost.
ARRL antenna expert Dean Straw, N6BV, says he's heard of at least one 2-element 160-meter wire Yagi. "A fellow in Czechoslovakia did it years ago," he says. "Jarda Dvoracek, OK1ATP, strung his inverted-V arrangement between two tall buildings, if I remember rightly." The article in the October 1975 issue of QST describing this beast leaves out details of the antenna's supports--there may have been a reason for that. Straw says such an antenna should probably be at least a half-wavelength above ground to show any gain--meaning it would have to be about 240 feet in the air!
Straw says the practical height above ground for a rotary Yagi on 80 meters--about 120 feet--is more practical, "albeit with a very rugged tower," he adds. "The really successful 80/75 meter operators using 3-element Yagis are located on top of tall mountains."
Another route
is to install sufficiently tall verticals in a phased or parasitic (ie, Yagi)
array. With two quarter-wave verticals (or their electrical equivalent, since a
full quarter wave is about 130 feet) spaced about a quarter wavelength apart,
you can devise a 90-degree phased array that will radiate in one of two
opposite directions at the flick of a switch. With three such towers (or even
wire verticals) appropriately sited, you can make up an array that will switch
in several directions. This is essentially the same technology that some AM
broadcast stations employ to change their daytime and nighttime patterns, if
required.
 The Ladder-Loc center insulator and support from Cable X-perts Inc is a good starting point to build your own doublet fed with 450-ohm balanced feed line. |
It's also possible to phase a couple of dipoles for any band and obtain a little gain and/or directivity using simple coaxial cable delay lines and simple switches.
How high should my wire antennas be? Ideally, for a given band, your wire should be at least one-quarter wavelength or more above the ground. Antennas up one-quarter wavelength will exhibit both low and high-angle radiation components. Lowering the antenna substantially raises the antenna's take-off (radiation) angle. A low-slung antenna generally means that most of your signal is taking off at a high angle--even straight up in the worst-case scenario--and returning to Earth fairly close to the transmitting station.
For those who desire a good antenna for local or regional communication, low wire antennas (also known as "cloud burners") exhibiting high radiation angles can be very effective. Visit the NVIS Web page of James Glover, WB5UDE for a description of Near-Vertical Incidence Skywave (NVIS is a term used to describe this particular type of propagation.)
For those interested in working DX, however, a low take-off angle is desirable for long-distance signal propagation, and--let's face it--most of us are looking to put some distance between us and the stations we work (ie, work DX). To optimize low-angle radiation, you might need to go up as high as one-half wavelength above ground (see N6BV's comments above).
Keep in mind here that we're talking about antennas sited above good ground. Unfortunately, all soil is not created equal when it comes to antennas. The downside here is that it's often not possible (or within the budget) to come up with the necessary supports to suspend your horizontal wire antenna that high in the sky. After all, we're talking 70 feet on 40, 135 feet on 80 and 275 feet on 160 meters!
Vertical Antennas
There's an old adage that says, "A vertical is an antenna that radiates equally poorly in all directions." This really isn't the case, however. Hams sometimes resort to vertical antennas for the low bands because the take-off angle is lower. You might be trading off some usable bandwidth, though, because verticals--especially for the low bands--tend to be electrically shorter than a comparable horizontal wire antenna would be.
For an excellent explanation of vertical antennas, read "Verticals Without Vertigo" by legendary antenna guru L.B. Cebik, W4NRL. The addition of a commercial or homebrew vertical to the QRPer's antenna arsenal can provide low-band coverage with radiation angles for working DX--although it's possible that for closer-in work, even a low dipole will outperform your vertical. In the ideal situation, having both a vertical and a horizontal wire antenna available can give the QRPer a much wider area of coverage on the low bands.
When choosing a low-band vertical antenna, my personal experience is that commercial or homebrew verticals that concentrate only on the lower bands work (or are even optimized for a single low band) perform much better than multiband verticals. A commercial example of this is Bencher's Butternut HF-2V versus their HF-9-V.
A key to success with vertical antennas is a good--no, excellent--system of ground radials. This is often the most overlooked part of a vertical antenna installation. More radials are almost always better, but don't reject the idea of a vertical if you can only put down a modest radial system. A "compromise" antenna certainly is better than no antenna at all.
There are a couple of tricks you can use to provide a radial system when there is no way to lay down lots of wires. One is to use an existing chain-link fence surrounding your yard or even an underground sprinkler system that has old style copper pipe. Mount your vertical on a metal or metal-roofed building or even tie it in electrically to the reinforcing bars (rebar) under your concrete patio or driveway before the concrete is poured. There probably is no substitute for a realradial system, however.
Remember to use caution when laying out
radial systems that children or even pets might come in contact with. Current
flows through these conductors even with our QRP-level RF, and the end of a
quarter-wave wire is a voltage node.
 Diagram of an inverted L antenna [ARRL Technical Information Service] |
Vertical Performance Without a Vertical Antenna
One of the most popular wire antennas on 160 and 80 meters is the inverted L. The inverted L is just what it says: an upside-down (ie, inverted) L-shaped wire with both a vertical and horizontal section. Here's another tip: you can create an almost-free vertical antenna by shunt feeding the tower supporting your HF beams. Some installations even electrically bond the HF rotary beam(s) as part of the tower for top loading--especially useful if the tower is electrically on the short side.
Separate Receiving Antennas
Due to typically higher noise levels on the
low bands--especially on 160 and 80 meters--many of the most successful
operators on these bands use separate transmitting and receiving antennas. If you have
the acreage, multiple Beverage (named after the inventor) antennas can allow
for optimized reception in specific directions. There's lots of information on
the Collection of Beverage Antenna
Information Web site of Glenn Swanson, KB1GW. For those
short on acreage, magnetic
loops, flag
and pennant receiving antennas may be suitable alternative low-noise
receiving antennas.
 The new Z-100 antenna tuner from LDG Electronics. |
Antenna Tuners
Many of the antennas discussed above may require an antenna tuning device. If your antennas is fed with balanced feed line (eg, "ladder line"), you will need a tuner and, preferably, a balun to tune your antenna system to your transceiver's unbalanced 50-ohm output. You can use either a standalone balun or one that's built into the antenna tuner (several models include these).
Baluns come in a variety of flavors. I would suggest a current type with a 4:1 or 1:1 ratio, but with a caveat: A balun is a transformer, and the actual impedance it sees at the end of your balanced feed line--say, for a typical dipole or Zepp--can vary wildly by band. So, the balun's specified 1:1 (ie, 50 ohms unbalanced to 50 ohms balanced) or 4:1 (50 ohms unbalanced to 300 ohms balanced) ratio might not mean much when the balun is seeing a complex impedance at the end of your feed line. In some cases the transformation is inefficient to the point that that you'll lose significant power in the balun. At higher power levels, such losses are manifested by heating in the balun itself.
That said, a number of commercial baluns, both kits and factory-built, are available. Instructions on homebrewing your own balun are in many antenna references. You also can visit the Web site of Tom Hammond, N0SS, for detailed, downloadable, instructions. You can skip the balun for your 40 meter antenna fed with balanced line if you build the BLT (Balanced Line Tuner) kit from the NorCal QRP Club.
MFJ sells a ready-built balanced-line tuner,
the model MFJ-974H.
Although it does not have a built-in balun, the Z-100 from LDG is a very
versatile automatic
antenna tuner that will handle power levels from QRP through 125 W. If you own
an Elecraft K2 you will definitely want to
add the KAT2 internal antenna tuner.
 The Emtech ZM-2 antenna tuner is available as a kit or prebuilt. |
A number of manual antenna tuners also are available to match your antenna and budget. These include the Emtech ZM-2 kit, which incorporates support for both balanced line and coaxial cable-fed antennas.
Other Tools
If you enjoy tinkering with antennas, I would strongly suggest acquiring an antenna analyzer. Three examples are the MFJ 259B and Autek's RF1 and VA1.
Reader Feedback and Author Comments
Thanks for the e-mails from many
observant--and early--readers of last month's column, which contained some
incorrect information before we realized the error of our ways and made
appropriate corrections. Since CW, RTTY and other data modes such as PSK31 all
are allowed on 30 meters, I should have said "All digital, all the time" in my
initial wording referring to that band. Also, the maximum power level on 30
meters is 200 W PEP.
 A prototype of the NOGAnaut transceiver. |
Scott McCullen, NJ0E, wrote to remind me of a great 80-meter project, The North Georgia QRP Club's NOGAnaut. The NOGAnaut is a very simple transceiver that uses inexpensive 3579.545-kHz TV color burst crystals or 3686.4-kHz microprocessor crystals.
If you're looking for a few QRP contests to participate in this year, visit the QRP Contesting page maintained by Ken Newman, N2CQ on the AMQRP Club Web site.
Hope to work you on the low bands this winter, QRP of course!
Editor's note: Anthony Luscre, K8ZT, an ARRL member, lives in Stow, Ohio. He has
worked in the field of medical microbiology for 18 years and is now a
Technology and Computer Coordinator for a local school district. Luscre is an
avid QRP operator having earned DXCC, WAS and WAC using no more that 5 W
output. Readers are invited to contact the author via
e-mail, and to visit his Web
site.
| Previous: Amateur Radio Antenna Bill in Play in Vermont | Next: It's Musical Chairs Again for Next ISS Crews |
