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I can hear it now, "What are you crazy?" I'm only using the Ham Cram site to prepare for the Technician class exam, why do I need a HF antenna? The are several reasons to get a HF antenna.
1. Technicians can use a portion of 10 Meter SSB which gives you the possibility to work DX through the world.
2. If you learn CW you can also operate on the former novice portions of 15, 40 and 80 meters.
3. Listening to DX on the HF bands is a big inducement to upgrade to General.
4. They are inexpensive and can even be built as a do it yourself (DIY) project.
5. They can all be installed using an inverted "V" configuration so you only need one support structure.
6. Only one feedline is required.
Please don't get trapped into the concept that ham radio is a rig on a belt.
1. Single band dipoles.
2. Multiband Off-Center Feed (OCF) Dipole
3. Trapped Multiband Dipole
4. "Fan" Parallel Dipoles
5. G5RV Type Multiband Antenna
1. A single band dipole, as the name implies, is resonate on only one band and works well on that band. Without much additional work, you can build, or purchase, a multiband antenna. A single band antenna is simple to build and erect. If you start after breakfast you can have it up before lunch time. However, versatility should be a desirable characteristic of your first HF antenna so let's shoot for a multiband antenna. Let's do a short review on the antennas as listed above.
2. An multiband off-center feed (OCF) dipole is a cut to be a half wave on the lowest frequency you intend to us with the feedline being connected somewhere other than the center of the antenna. The center feed point impedance of a half wave dipole is approximately 50 ohms so it's a good match for relatively inexpensive coaxial cable. As you move either side of center the impedance increases. Using ladder line and an antenna tuner you can give the antenna multiband capabilities. Having said that, matching the feedline and adjusting the overall length of the antenna can be somewhat tenuous. Construction of an OCF antenna is probably not a job for someone new to antenna construction. I have no practical experience with OCF antennas experience but I've seen others have a very difficult setting one up for multiband use. Moving the feedline within the antenna is error prone and cumbersome.
3. Trapped multiband dipole. A trap is an inductor and capacitor that is resonate at a frequency within a band. They are always used in pairs except in vertical antennas. An example will serve to illustrate. Let's assume you have a 20 meter conventional dipole and you want to add 40 meters to the antenna. You would put one trap resonate on 20 meter at each end if your existing antenna. An inductor and capacitor in parallel resonate at 20 meters would represent a high impedance at 20 meters. Any wire on the far side of the traps is electronically not there on 20 meters. The inductance of the trap serves to shorten the overall length of the antenna on 40 meters, therefore a 20/40 meter trapped antenna would be shorter than a 40 meter single band antenna. Unadilla makes very high quality traps but they sell for between $44 and $48 a pair depending on band. You can also build your own trap antenna. See building your own trap antenna It can be a daunting task. I have built a trap antenna for 20, 40 and 80 meters using Unadilla traps and it worked very well.
4. A “fan” antenna is simply a group of half wave resonate antennas feed from a common feed point. Of all the antennas described this ham cram tutorial this type of antenna has the least compromise although there is interactions with the higher frequency antennas. See an excellent article on fan dipoles I have built several of this type of antenna with very good results. You can build your own spacers or purchase commercial spacers online. A good source of solderless spacers is 73CNC.COM.
5. G5RV type multiband antennas. I've saved the best for last. For an explanation of the G5RV design see the G5RV Wikipedia page The G5RV, and its variations, are arguably the most popular antennas in the world. In the interest of full disclosure I have installed three of the ZS6BKW variant of the basic G5RV design and it is by far and away the best wire antenna I have ever used. I have one using an inverted V configuration in which the apex is at about 35 feet and then ends drop down to about 7 feet. I installed one for my 12 year old grandson, W3WKV, mounted in a tree about 45 feet at the apex and the end drooping to about 7 feet. Within 6 months of being licensed as a general (he aced both the Technician and General testw using the ham cram method) he worked over 50 countries and over 40 states with a barefoot 100 watt rig. Ready to hang antennas are available for $76.00 from W8AMZ.com The construction is extremely rugged, there is no exposed wire and my ZS6BKW/G5RV from W8AMZ.com survived hurricane Sandy without a scratch which is more than I can say for my house. It would cost almost as much for component parts if you wanted to build this antenna on your own.
There are two hidden costs. If you want to operate all bands from 6 to 80 meters you will need an antenna tuner. Using the built in antenna tuner on a Yaesu FT450 the Standing Wave Ratio (SWR) is under 2:1 on all bands including 60, 30 and 6 meters. You will also need at least 70 feet of 50 ohm coax cable to complete the matching section. If you decide to get this antenna make sure you get the ZS6BKW/G5RV version.
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