Showing posts from January, 2014

Simple Ham Radio Antennas: Antennas without tuners, part 4. Post #257

So far, the "tunerless" antennas I've built have worked very well.  They have been made with locally available materials from my "junk" box, neighborhood garage sales, and the nearby Ace Hardware Store.  These antennas have consisted of individual dipoles/inverted vees for my bands of preference (40, 20, 15, 10 meters), telescoping fiberglass masts (33-ft/10.06 meters tall), a single RG -8X coaxial feed line , and supporting wooden stakes or tree branches. Dipoles for each band were built on the ground and were later hoisted into position via a halyard and pulley system.  A "choke balun" made from part of the RG-8X feed line was attached to the mast just below the center connector at the top of the mast. In my first multiband antenna system, I changed bands by lowering and raising the appropriate antenna into place.  I couldn't change bands by staying in the shack. My second system was a modified "fan dipole/inverted vee" using mul

Simple Ham Radio Antennas: Antennas without "tuners", part 3. Post #256

In some of my previous posts, I've investigated, built, and used multiband dipole and inverted vees using a single 50 ohm coaxial feed line .  With a telescoping fiberglass mast (33-ft/10.06 meters extended), a simple halyard and pulley system, and separate antennas cut for each band of use (40, 20, 15, and 10 meters), I've been able to change bands fairly quickly by lowering the dipole/inverted vee elements, substituting those of another band, and raising the new antenna.  With each band element cut for the desired frequency, the efficiency is high with low swr for that band.  Since each antenna element is trimmed for the lowest swr at my mast location, an antenna transmatch isn't necessary.  Sometimes, as in the case with the 40 meter dipole/inverted vee, an antenna cut for the cw portion of the 7 MHz band will often work well on the phone portion of 15 meters (21 MHz band). The 15 meter band will operate on the third harmonic of the 40 meter band . In order to save

Simple Ham Radio Antennas. Antennas without "tuners". Part 2. Post #255

One of the more popular amateur radio antennas is the multiband "Fan Dipole" and its close relative the multiband inverted vee "Fan Dipole."  According to Howard (W6HDG), the Fan Dipole "consists of  two or more distinct half wave dipoles which are mounted to a common parallel feed point so that a single feed line can be utilized."  With a little ingenuity and careful trimming, it is possible to make a single band dipole antenna work on several bands just by adding half wavelength dipoles for your favorite band to the center coax connector and by "fanning them out" below the dipole for the lowest frequency.  Add a 1:1 balun or a "choke" balun below the center connector, connect some 50 ohm coaxial cable, run the cable to your rig, and you're ready to go on your favorite bands without a "tuner" and a ground radial system. According to Simone (IW5EDI), "an antenna like this works on multiple bands because the antenna

Simple Ham Radio Antennas: Antennas without "tuners", part 1. Post #254

Antenna transmatches or "tuners" are wonderful devices that make amateur radio operations easier.  They can help minimize swr on antenna feed lines and extend the band coverage of your present antenna. However, there are times when such devices may not be needed, especially if you're designing an antenna for a single band or are contemplating an emergency or portable antenna for your "go" kit.  By carefully designing, cutting, and trimming your basic 1/2 wavelength dipole for the lowest swr, you can just connect a good quality 50 ohm coaxial cable feed line and run the band of your choice without much difficulty. In this post, I will describe a few simple coax-fed dipoles and inverted vees that will serve your favored amateur radio band without the need for an antenna transmatch .  Of course, you could always insert a transmatch into the system to squeeze out the maximum power at the lowest possible swr if you so desire.  These antennas work either way.  

Simple Ham Radio Antennas: When to use antenna tuners. Post #253.

Nowadays, the antenna transmatch ("tuner") is an integral part of many amateur radio stations.  With this device, a ham can match the output of his/her transceiver with the often unknown impedance of the antenna itself.  With a suitable balun (balanced to unbalanced) transformer, it is possible to use one antenna to cover several HF bands, especially if you're facing space restrictions on a small lot or have  to operate in "stealth" mode because of HOAs and CC&Rs.  This situation applies mostly to the use of 300 ohm tv twin lead and 450 ohm ladder line, which require a balun (1:1 or 4:1) and antenna transmatch to operate as feed lines in a multiband, single antenna system. There are times when you may not have an antenna "tuner" at your disposal, especially if you're operating in portable or emergency situations.  In my case, I remove my Drake MN-4 and MFJ 941-E transmatches from the antenna system for routine maintenance several times a

Simple Amateur Radio Antennas: Your first antenna. Post #252

The New Year is the time of new beginnings.  It's time to try new modes, perhaps a new rig, and even a new antenna.  At the KH6JRM ham shack, the new year got me thinking about the first antennas I built as a novice operator back in 1977.  Some of those halting first steps were a disaster--high swr, no contacts, rf in the shack. You name it, I had it when it came to homebrewed antennas. Perhaps those of you who are recently licensed can understand my frustration when my knowledge fell a little short in the antenna department.  Thankfully, there are a variety of books, internet sites, and amateur radio clubs that can help the new operator with antenna questions.  But, back in the days when I lived in a fairly isolated location on Hawaii Island, about the only thing I could refer to was the ARRL Antenna Book and my own experimentation.  After a while, my antenna notebooks showed some improvement as I finally understood how antennas are built and used.  Keeping an antenna notebook