The Possibilities are Endless

Transcription

1 The Possibilities are Endless An article on what antenna to use when starting out in ham radio. So, you just got your shiny new license and now you can start exploring the bands and get on HF and work the world. The possibilities are endless and with a brand-new transceiver that can work from DC to Nano waves, you pretty much have it all figured out, right? Then reality sets in. The propagation conditions are terrible and when you hook the radio up to a hunk of wire, it doesn t hear anything and you re disillusioned. That s when you remember what the instructor told you that it doesn t matter what you use for a radio, if it can t transfer the energy to the rest of the world, then it s pretty much an expensive doorstop. So how do you transfer that energy both in and out of the radio? With a transmission line connected to a radiating element otherwise known as an antenna. That s why the most important part of the whole system is the antenna. With a poor antenna system, you can spend as much as you like on the new rig and all you ll hear is noise or nothing at all. Probably the most common question I get asked when teaching Ham Radio is what s the best antenna to use when you re starting out? Well, that depends on what bands you want to listen to and communicate on, of course. If you want to communicate on 2M or 70cm then high-quality transmission line running directly to a good, high gain antenna is a great choice. The better the coaxial cable you use, the lower the loss, so don t skimp here. Get the good stuff if you are running it any appreciable distance from the transceiver. Remember that the more gain the antenna has, the more it will overcome any losses in the transmission line. I want to stress that a VHF or UHF radios work well out of doors but are marginal when inside the house. I ve seen and heard so many new hams and seasoned ones too, become disillusioned when their brandnew handhelds don t work very well from inside the house. Of course, they don t. Remember the physics of it all folks. VHF and UHF are line of sight radios generally and when you put them into a house with stucco or aluminum siding on the outside or even just wooden frames, they are being operated inside a faraday cage. Put an outside antenna up and stop trying to use that little rubber ducky as an antenna inside your house. So, while talking about handheld radios, ditch that antenna that came with it. Use it as a cat toy or something. It s nothing more than a wet string in terms of efficiency. Get an inexpensive whip antenna for it instead from a reputable dealer. Comet and Diamond make good ones at reasonable prices. They aren t dx antennas, but they ll get you out locally and you ll hit the repeaters with them. Remember that VHF and UHF are line of site frequencies. If you can t see it, it can t see you. Oh, and one other thing Don t believe the specs you get on those cheap radios from the far east. They generally are a lie and most of the ones that I ve tested don t come even close to the published specs. 1

2 After all their motivation was to sell you a cheap radio and they were successful at that. You get what you pay for. If you are going to buy a handheld, buy one from a reputable dealer and manufacturer. Yaesu, Kenwood, Alinco and Icom for instance sell radios that have great specs and they meet them. They might cost a bit more, but they work and are reliable and that s what it s all about. And boy do they last. I ve had an old Yaesu VX5R handheld that I bought in 1997 that still works perfectly, and still meets its specs. The other thing is to try to get that antenna up as high as you can. An excellent choice would be to put it up on a roof mount on your house or on a pole. Roof mounts are inexpensive and can be bought from radio dealers. Make sure the mount is sealed properly when you put it on the roof with roofing tar sealant and bolted firmly so that it doesn t work loose in the wind. Also ensure your antenna is firmly connected to your transceiver by putting the connector on correctly, tightening it and protect it with sealant or vulcanizing rubber tape. This goes for any antenna you might want to use out of doors. For a selection of good VHF and VHF antennas, check with the dealers. Diamond and Comet make great vertical antennas that are easy to use and have good gain and are relatively inexpensive. If you re interested in more directional antennas, then look at Hygain or Cushcraft beam antennas. With a beam antenna, you ll increase the gain to and from your rig and provide some selectivity in terms of direction. Once again, the better the transmission line the better the gain. Remember to keep your coax dry. Beam antennas are often mounted on a rotator. Inexpensive, TV antenna type rotators work well for light VHF and UHF antennas, however if you are putting more than one antenna on the pole, you ll need to get a more robust rotator or fashion a thrust bearing to take the lateral pressure off the TV rotator. Even low-cost rotators new will cost you a couple of hundred bucks, so protect them from damage by doing it right. Rotators are also available from radio dealers such as Radio World or GPS Central in Calgary. Another source is flea markets, but buyer beware. It may be cheap, but there may be a reason for that too. So, what about HF? There are so many options available to both new and seasoned hams that the choice is often dependent on the following questions. How big is the area that you can use to put up your antenna? What bands do you want to work? Are you just interested in working locals such as North American stations or are you interested in working some dx. What modes do you want to work? Can you put up a tower or some other structure to hold your antennas? Do you want directional antennas or are you interested in just putting up a wire and work the local nets on 80M or 40M? What can you get away with, without annoying someone? (wives, girlfriends, landlords) And, of course, what can you afford? So, let s look at some possibilities. Let s assume you want to work locally. That would include the continental US, Mexico and Canada on the HF bands from 80 to 10 meters. 2

3 The first choice is a simple dipole. Dipoles are easy to build and work very well but are restricted to a single band only. A variation of the dipole is the inverted V. A dipole is strung between two supports whereas the inverted V is supported in the centre only. Remember, however that they only work on one band and it doesn t matter if you use an antenna tuner to fool your transceiver into thinking it has a match, it will not be an effective antenna on bands it is not cut for. Another simple variation of these antennas are fan dipoles. Because dipoles are resonant only on one band, the fan dipole is a bunch of them cut to be resonant on each band you want to work and use the same centre feed point. Refer to the dozens of articles available on the internet to see variations of these antennas and what others are doing with them via YouTube. A great antenna to start out with is a simple long wire otherwise known as a random length antenna. Typically, they are cut to a nonresonant length and fed with a 9:1 unun. They also have a counterpoise attached or use the coaxial line out to the antenna as a counterpoise instead. These antennas work well and can be used on all bands using an antenna tuner to tune the reactance out of the transmission line. They can generally be used from 160M up to 10M. You can mount them in just about any configuration and the most common way is to attach a random length of wire to a weatherproof box containing a 9:1 unun mounted on a fence post. The antenna wire then is supported at the other end by tying it to the top of a tree with a rope. They re simple to build and effective although they seldom will work as well as a dipole or inverted V. But, you re on the air at last. These antennas are available commercially too. Another effective, compromise, all band antenna is the G5RV. These antennas are easy to build and work reasonably well from 80M to 10M. They are really a shortened dipole antenna with a 300 or 450-ohm ladder line matching network feeding them and then 3

4 are connected to coaxial line. Once again, you ll need a good antenna tuner to match the line to the transceiver. G5RV s are used all over the world and are effective for local communications in North America and beyond when the sunspot cycle is cooperating. I have worked the world with a G5RV. They are also available commercially. And then there are vertical antennas. A vertical antenna is generally a quarter wavelength high and attached to a good ground at the base. Many of the commercial ones use coils and matching stubs to tune them to make them resonant on each band. Commercial verticals are usually expensive but generally easy to get working and seldom need tuning. Some don t need ground radials to make them effective and my experience with them is that they are once again a compromised antenna in those configurations. Vertical antennas are good dx antennas and I have worked the world with one made by Butternut mounted in my backyard. Vertical antennas are usually shorter than a quarter wavelength high on the lower bands and need some type of loading to make them effective and therefore with a ground image appear to be a half wave antenna electrically if you have a good ground. They are quiet if they are in the clear away from other antennas and power lines and other urban noise sources. The key is to put down a good radial system around the bottom of them. The more radials you put down the better because it effectively reduces the angle of radiation which makes it a better dx antenna. In my case, I have 24 radials varying in lengths from the lowest band to the highest and have worked the world on all bands using it. And while I m mentioning radials, I learned something many years ago about laying them out on a lawn. A common misconception is that you must bury your radials under your grass or you ll be constantly tearing them up when you cut your lawn. Nothing could be further from the truth. If you stake your radials out from the antenna using a long nail at the end of them to hold them taut, and simply lay them on the top of the grass, they ll become absorbed by the grass within a week or so. They ll magically disappear below the thatch if you just cut your grass a bit higher for a while and leave the thatch. Shortly you will not see them or tear them up with the lawnmower. Neat trick eh? And it ends the prospect of cutting long trenches and pushing wires into them in your lawn. 4

5 Another commonly used vertical antenna is the 43-foot vertical fed with a 9:1 unun. If this sounds familiar, then you will recall that the random length antenna mentioned above uses the same configuration. 43 feet is a random length that isn t resonant on any ham band and therefore can be used as an all band antenna for the ham bands. With a good ground plane like a radial field they are very effective as a dx antenna and are significantly cheaper than other commercial antennas. By the way, you can make a 43-foot antenna out of fence post galvanized steel pipe commonly available at Home Depot as fencing or aluminum tubing and sit it on a coke bottle fed with a 9:1 unun. Simply cut it to length and hold it vertical with Dacron rope tied to the middle. Don t forget the radials. Use your imagination with this to come up with other variations. A word of caution though, make sure your dog doesn t pee on the base while you re transmitting. If you are transmitting 100 watts at 50 ohms and transforming it to 450 ohms or higher, the results could be illuminating. Remember your formulas? In terms of directional antennas for HF, look at the ARRL Antenna book to see what others are doing. It all depends on the bands you are interested in working. There are dozens of beam antennas for all the bands available, although a beam on 80M and 40M are a bit cumbersome and you need a big rotator to turn them as well as lots of real-estate. Typically, multi band and less cumbersome monoband beams are readily available for 20M and up. Commercial ones are available from Cushcraft and Hygain and are reasonably priced. Others are made by Optibeam and the fully tunable StepIR beams. Remember, though, that the bigger the beam, the bigger the rotator to turn it. And now you re talking putting up a tower to hold the array and the added cost of cable for the rotator and a climbing belt and gin pole and all the other accessories. A very reasonably priced, effective beam antenna that has become popular lately is the hexbeam. A hexbeam is a wire antenna that looks like it should have laundry hanging on it. Put it on a 30-foot tower and turn it with a light duty antenna rotator and you have an excellent dx antenna that will allow you to work the world. Hexbeams are usually made with fibreglass spreaders and therefore are light. They provide you with the same kind of gain as a three element yagi but are not as big in terms of footprint and don t need to be very high to be effective. In fact, I have worked European stations while it was on a five-foot ladder in the backyard. Most that you can buy 5

6 commercially cover 20M to 6M or higher and weigh about 20 lbs. They come as kits and cost around $500 and take about an hour to assemble. Another antenna that has become popular lately is the magnetic loop. These are a small footprint antenna that are very effective in a small space. Typically, magnetic loops are only a few feet wide and are often mounted on a pole only a short distance from the ground or inside your house. If you re stuck inside an apartment or somewhere that you can t or don t want to put a bigger antenna up, then the magnetic loop is ideal. Magnetic loops are available commercially and work very well. They are not cheap, but then again neither is a full-sized beam. They re quite directional and can be used on all the bands with varying degrees of efficiency. A magnetic loop is nothing more than a very high Q circle or octagon of metal tubing and is tuned with a high voltage variable capacitor or sometimes a vacuum variable. Because they re such a high Q, they are sometimes difficult to tune because the peak is so sharp. The word of caution with them is that on parts of the antenna, the RF voltages can be extremely high and you don t want to be touching them when you re transmitting. Many people have built them and there is lots of information about how to do so on the web. They re commercially available with one of the best coming from MFJ that has an very effective controller with a cross needle SWR and power meter. So, in conclusion, my suggestion is that if you are anxious to get on the air and start your career in amateur radio or are hampered with a lack of space, then look at some of the suggestions above. Each one comes with its own package of considerations. I have used all the antennas suggested over more than 50 years of being a ham and they all work. Get on the web and read what others have done and decide on what is going to work for you in your circumstances. Read the ARRL Antenna manual and get even more ideas. Be prepared to experiment and have some fun building your ideas. There is no better way to learn what does and doesn t work than by trying it. Be skeptical of outrageous claims by manufacturers and others that purport their antenna works dx where nobody else can hear the station. Think about the physics. Learn your craft. But, most importantly, get something up in the air and get on the air and work the world. We ll be listening for you. 73 Tom VE6ARG 6