Showing posts from May, 2013

Antenna Topics: A simple, indoor multiband dipole antenna. Post #197

Over the past few days, mother Nature has released a torrent of heavy showers over the Hamakua Coast of Hawaii Island, making outdoor antenna work very wet and potentially dangerous.  When the weather turns bad, I usually lower all my verticals and inverted vees to ground level, disconnect antenna feed lines, and unplug my rig from the electrical mains.  I usually run my station off of deep-cycle marine batteries charged by photovoltaic panels, but sometimes, I use the electrical grid to run a bit more power (i.e. more than 50 watts) from my venerable Swan 100-MX. During today's passing showers, I decided to revive one of my old indoor antennas, a 10, 15, and 20 meter segmented dipole fed by a short piece of 50-ohm cable (RG-58).  This certainly isn't a new idea.  I've used the concept for outdoor antennas as well.  You can choose which of these bands to use by clipping or unclipping dipole segments.  AK7M and NV5I have published versions of this antenna in various ARRL

Antenna Topics: Reworking a basic 10 meter ground plane antenna. Post #196

Reworking a basic 10 meter ground plane antenna. After two fun-filled days of experiments with my horizontal 10 meter dipole, I decided to lower both masts, disassemble the dipole elements, and store them in the garage for possible emergency or portable use.  For some reason, the second mast made my "antenna farm" noticeable from the street and I opted to use only one mast for my next 10 meter antenna project.  I selected the fiberglass mast with the light green paint for antenna projects because it blended in well with the garden and the surrounding vegetation.  The spare MFJ mast would be used as a backup and emergency mast. Still, I wanted to work a bit more with 10 meters, which has shown some excellent propagation during the past month.  I had already used a 10 meter vertical dipole with great success during the past year.  This time, I wanted to experiment with a 10 meter ground plane antenna that could be easily built, erected, and taken down without undue problem

Antenna Topics: A simple 10 meter dipole. Post #195

A simple 10 meter dipole antenna. One of my favorite amateur radio bands is 10 meters.  It's unpredictable, capricious, and fun!  When propagation is favorable, you can works the world at QRP levels.  Basic antennas for this band are simple, cheap, and forgiving.  Most of the parts needed for this antenna can be bought at your neighborhood hardware store or home improvement outlet. Although 10 meters has been a bit sporatic over the past few days, I've been able to make some good contacts during daylight hours from my location on Hawaii Island--the island with the active Kilauea Volcano.  We live dangerously over here. MATERIALS: Two fiberglass or pvc masts, ranging from 20 to 30 feet tall (6.09 meters to 9.14 meters).  These masts will support the 10 meter half-wavelength "flat top" antenna.  Fortunately, my backyard can support two masts approximately 30 feet (9.14 meters) apart.  Anything more requires my dipoles to be in the inverted vee configuration.  F

Antenna Topics: A simple 15 meter vertical dipole. Post #194

A simple 15 meter vertical dipole. One of my favorite amateur radio bands is 15 meters.  The band is usually open during daylight hours and provides plenty of DX for those of us operating from the central Pacific.  Although most of my antennas are designed to be used on several bands (using ladder line, a 4:1 balun, and an antenna matchbox or "tuner"), I sometimes want to use an antenna specifically designed for a single band using whatever coaxial cable I have around the shack. In my location, I prefer using verticals, inverted vees, and loops because my backyard is small and room for a decent radial field is non-existent.  If I can't use a horizontal flat top dipole, I can always go up using a vertical dipole.  These antennas are simple to build, erect, and take down.  They are ideal for portable use with a telescoping fiberglass or pvc mast.  Once I finish testing a vertical dipole for a chosen band, I keep the pre-assembled antenna in a plastic storage box for fu

Antenna Topics: RG-6 coaxial cable for antenna feed lines. Post #193

RG-6 coaxial cable--an alternative to RG-8X, RG-58, and RG-8. Most amateur radio operators are familiar with the RG-8, RG-8X, and RG-58 family of coaxial cables.  These moderately priced cables are used for antenna feed lines and patch cords around the ham shack.  With a nominal impedance of 50 to 52 ohms, they work well with both contemporary transceivers and the old "boat anchors" we love to hate.  Many amateurs (such as yours truly) also use 300-ohm tv twinlead and 450-ohm ladder line to feed our antennas. With a suitable transmatch and a 4:1 balun, we can use an antenna on several bands. What if you don't have any ladder line, tv twinlead, or 50-ohm coaxial cable to feed your antenna?  Is there any other cable that can be used?  There certainly is.  RG-6 coaxial cable, the type used by cable companies , can often be used the same way as 50-ohm coaxial cable.  RG-6 usually refers to a cable with an 18 AWG center conductor and a 75-ohm characteristic impedance.  Us

Antenna Topics: A simple 40 through 10 meter delta loop. Post #192

A simple 40 through 10 meter delta loop. One of the quietest and most versatile antennas I've used over the past few years has been a 40 through 10 meter delta loop fed with 450-ohm ladder line.  Used with a 4:1 balun, an antenna matchbox (i.e. "tuner), and a few feet (meters) of 50-ohm coaxial cable, this easy to build antenna will give you hours of both local and DX contacts. I built my original 40 meter delta loop with tuned feeders back in 1977, shortly after I passed my novice amateur license exam.  Since space was at a  premium (small backyard), money in limited supply (I was just starting my broadcast radio career after time in the Air Force), and I was recently married, extra funds for a tower and a super sophisticated rig were unavailable.  Like many of my fellow amateurs, I depended on wire antennas, used rigs, and basic designs to work the world.  My first rig was the venerable HW-101, a rig I must have rebuilt several times. Anyway, I found simple antennas,

Antenna Topics: A multi-band half-wavelength sloper covering the 40, 20, 15, and 10 meter amateur radio bands, post #191.

A multi-band half-wavelength sloper antenna. This has been another beautiful, slightly windy day on Hawaii Island--a perfect time to build another antenna for DX adventure.  Although I've been happy with my 40 meter vertical with tuned counterpoise, I wanted to experiment a bit with another antenna I used frequently in my novice license days almost four decades ago. I quickly found my antenna experiment log book on the shelf of the radio room and turned to the pages marked "November-December 1977."  Those were some unusually dry months at my old QTH in Honokaa.  I was able to build several working verticals, loops, and slopers for my then new novice station. By feeding the sloper with 450-ohm ladder line and a 4:1 balun, I was able to cover three novice segments  in the 40, 15, and 10 meter amateur radio bands with few problems.  I knew the antenna would work on 20 meters, but I didn't hold a higher license (i.e. general, advanced, or extra class) to  qualify f

Antenna Topics: A 20 meter vertical antenna with tuned counterpoise, post #190

KH6JRM's Amateur Radio Antenna Topics: A 20 meter vertical antenna with tuned counterpoise. This weekend has been outstanding on Hawaii Island.  Weather conditions were partly sunny and a bit cooler, thanks to the return of gentle trade winds.  Most of the vog (volcanic smog) has been blown off and most of us can finally breathe normally.  In other words, this was a grand day to build antennas. In my last post, I described a 40 meter vertical with tuned counterpoise that has performed well on the 7 MHz and 21 MHz amateur radio bands (the 15 meter antenna uses the third harmonic of 40 meters and works as a 3/2 wavelength antenna on 15 meters).  Since I built the antenna for the 7.088 MHz Hawaii Afternoon Net, it functions well around 21.264 MHz in the SSB portion of the 15 meter band. Now that I've enjoyed some success with this vertical, I decided to make another vertical antenna with a tuned counterpoise for 20 meters, concentrating on a frequency of 14.200 MHz.  Like

Antenna Topics: A simple inverted vee dipole that doesn't require a tuner, post #189

KH6JRM's Amateur Radio Antenna Topics: A simple inverted vee dipole that doesn't require a tuner. Hawaii Island has been enjoying some excellent, if somewhat voggy, weather the past few days--a perfect time to design and build a simple antenna for my favorite amateur radio bands.  Although I enjoy working 10 and 20 meters, I've found plenty of contacts and even some decent DX on the 40 and 15 meter bands.  During the day, there are plenty of Hawaii hams to chat with on a variety of nets.  Early afternoon chats on 15 meters range from locals to the exotic realms of the southwest Pacific and Japan.  If I decide to work 10 or 20 meters on a whim, I can always switch to my 40 meter vertical with tuned counterpoise to capture a few elusive contacts on 10 meters.  This antenna uses tuned feeders (450-ohm ladder line) and can work amateurs from 40 through 10 meters with the help of a 4:1 balun and a good transmatch, such as my Drake MN-4. However, this week, I've had th

Antenna Topics: A tuned counterpoise antenna for 40-10 meters.

KH6JRM's Amateur Radio Antenna Topics: A tuned counterpoise antenna for 40-10 meters In my last post, I related the experience of making a segmented inverted v dipole antenna covering the 20, 15, and 10 meter bands.  The antenna required some adjustment, particularly in the 20 meter segment, which was cut a bit short.  With all the segments connected together with alligator clip leads, I found the 20 meter section approximately 5 inches (12.7 cm) short on each side.  With the addition of some extra wire, the 20 meter section tuned up nicely on 14.200 Mhz.  It pays to cut your antenna elements a few inches (several centimeters) longer than expected. After using the segmented v for a few hours, I lowered the mast and stored the antenna segments in some plastic storage bins near the radio room.  I can reassemble this antenna again if the need arises. A NEW ANTENNA Since my backyard is rather small, I prefer verticals, inverted vees, and loops for most of my HF work.  The on

Antenna Topics: A 20, 15, and 10 meter segmented inverted vee dipole. Post #187

KH6JRM's Amateur Radio Antenna Topics: A 20, 15, and 10 meter segmented inverted vee dipole. In my last post, I described a 40/15 meter inverted vee dipole using aligator clip leads and short pieces of wire to improve the SWR on 15 meters.  The short additional length of wire on each end of the inverted vee lowered the SWR for 15 meters and provided a slightly better match for the RG-8X coax used as the feed line.  When I wanted to use 40 meters, I just unclipped the short lead.  By selecting the correct length of wire for each band and using the clip leads to add or subtract a small amount of wire length, I was able to use this antenna without an antenna match or tuner. This past weekend, I was able to modify this idea to get an inverted vee that would cover 20, 15, and 10 meters without a tuner.  As in the case with the 40/15 meter inverted vee, I incorporated some ideas from Edward M. Noll (W3FQJ) and Larry Barry (NV5I) to make a homebrew tri-bander inverted vee that has

Antenna Topics: A simple multi-band inverted V dipole for 40 and 15 meters, post # 186

KH6JRM's Amateur Radio Antenna Topics A simple multiband inverted V dipole for 40 and 15 meters. If you have a small backyard and only have room for a few antennas, a segmented inverted V dipole covering two to three bands of your choice is an option worth considering. It is quite easy to build an inverted V dipole antenna for two-band operation, with each leg of the dipole separated by a ceramic or plastic insulator.  A jumper clip associated with  each of the two insulators is closed for 15 meter operation and left open for 40 meter operation.  While 15 meter operation is possible with just a 40 meter inverted V (using the third harmonic of your 40 meter frequency), you could risk high SWR on 15 meters, depending on what 40 meter frequency you use. For example, a few years ago, I used my coax fed 40 meter inverted V on 15 meters with few problems since my prime 40 meter frequency was 7.088 Mhz ( the frequency of the Hawaii Afternoon Net).  With the antenna cut for 7.088

Antenna Topics: A simple 15 meter vertical dipole, post #185

KH6JRM's Amateur Radio Antenna Topics: A Simple 15 meter vertical dipole. Like many of my fellow amateur radio operators I'm "horizontally challenged" by a small lot without many trees or tall structures to support a half-wavelength, flat top dipole.  So, I've usually resorted to inverted vees, small loops, and random length wires.  All of these antennas have performed well, considering the lack of space available.  I've also tried verticals, with uneven results.  With a good radial or counterpoise system, vertical antennas can do a good job.  Perhaps, I'm getting old, but I don't get excited putting radial wire in my backyard.  Although I've used elevated counterpoise wires with some success, I just don't enjoy running wire all around my back yard, especially with neighbor children and pets running around.  Besides, the ground conductivity in my area is very poor.  The thought of "planting" a large number of radials in my small