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Author Topic: Dipole Selection Help!  (Read 635 times)
KB0ETC
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Posts: 248




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« on: October 07, 2001, 04:43:11 PM »

I am trying to select a dipole for this QTH.  I have read all the reviews for several antennas.  I am currently running a Gap Titan DX Vertical.  I'm confused!

I was renting the house we live in, so I purchased a vertical, now we own the house.  It sits on 1/2 acre in a city lot, with lots of tall Oak trees.  The yard is secluded with trees so wires running everywhere would not be visually obtrusive.

I am looking to put a wire up.  I am looking for help to select one.

I have been eyeballing three antenna:

1. The Carolina Windom 80
2. Alpha Delta (DX-CC or the DX-LB Plus)
3. the Van Gorden G5RV.

Cost really isn't a factor.  But performance is!  I want an antenna that will cover 80-10 meters, and the WARC band.  160 meter coverage would be a bonus.  I am running a Palstar AT1500CV Tuner, with a Yaesu FT-990 rig.  The external tuner is nice, but want an antenna that can be tuner by an internal tuner in the rig.

Also I plan on running Davis RF R9914F Coax to the antenna (since I have about 100' left over), it will be mounted at about 60' from the center, and 25' at each leg.

I want the best performance antenna at only 100 watts of less.   Amplifier will be added to the shack someday.
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G4AON
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Posts: 518




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« Reply #1 on: October 07, 2001, 04:56:34 PM »

If you want to coax feed the antenna, then you won't get a good SWR on more than one or two bands.

For a good low cost multi-band antenna you need look no further than a reel of insulated wire and some plastic conduit for spreaders. The cost is minimal and the performance very good on the lower bands (18 MHz and above the side lobes cause the signal to be radiated in too many directions).

An 80m to 10m antenna can be made from a 100 foot top, fed in the centre with open wire line. The wire I use is 1mm cross section PVC insulated wire of 32 strands. The wire seems to survive the winds quite well. The length of the top isn't critical.

Open wire spreaders can be made from plastic oval electrical conduit, cut to 6" lengths and drill a hole through the oval sides and thread onto the parallel wires. If the line is fairly tight you need less insulators.

I tune mine through a home wound 4:1 balun on the outside wall of the shack, 2 to 3 feet of coax straight into the shack.

The antenna tunes to a good SWR on all bands from 80 to 10 using a Z-11 auto ATU.

Dave
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AC5E
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Posts: 3585




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« Reply #2 on: October 07, 2001, 06:02:00 PM »

HI: All I can tell you is my personal experience with the antennas you mentioned.

I used the Alpha Delta DX-CC with excellent results.   I had to trim the outer sections a bit to resonate on the 75 Meter DX window, and the 10 Meter wire was also resonant in the low end of the band and had to be trimmed an inch or so. Otherwise - mine was up five years with excellent results and no problems. Although, to be fair, it's not much on 160.

  Except for 160, the Carolina Windom also worked well but got rather "lobey" on the higher bands. The mismatch on ten was great enough to cause a noticable reduction in recieved signal strength - and a tuner does not help because it's on the wrong end of the coax. However, most of us have plenty of recieve gain so that's not usually a problem.

  The G5RV is a better antenna than either of the above on 20, slightly less antenna on 40 than either of the above, much less antenna than either of the others on 17 and up - and essentially a leaky dummy load on 75 and 160.

  Hope this helps

  73  Pete Allen  AC5E
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KF9VH
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Posts: 72




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« Reply #3 on: October 07, 2001, 07:10:04 PM »

I have a G5RV and am very happy with it. The only band it has problems with is 15 meters. It works great on all the other bands. I am here to tell you it works just as good on 75 meters as a wire cut for that freq.. I have had both up. For the price you can not beat this antenna.
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KF4HEY
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Posts: 172




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« Reply #4 on: October 07, 2001, 08:36:15 PM »

I have a shortened G5RV that I purchased from Maple Leaf communications (http://www.mapleleafcom.com/g5rv.htm).  It works well on all bands with a tuner. The 2:1 SWR range on 80 meters is rather narrow and parts of the 80 meter band cannot be adequately tuned, but other than that it gives very good performance for the price.  It can be installed as a vee or flattop with about the same performance.
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N6AJR
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Posts: 9890




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« Reply #5 on: October 08, 2001, 05:51:36 AM »

Why don't you make a multi band dipole with a single feed point. You can feed this with a store bought balun , a 6" dia, 10 wind of coax balun, or no balun at all. Better yet, you make it your self and it is cheeeeep.

You cut wire, ( any kind long enough and strong enough) to dipoles for each of the bands you want to work . That could be as short as 19 5/8 inches per side for 2 meters,  then I think its around 54 inches each side for 6 M, ( check that one..) 8' 6" for 10 m,
12'9" for 15 m(or you could use the 40 meter one, it works well on 15 m) 17 ' for 20 m, 33' 6" to 34  ' for 40 m , 66 to 67 feet for 80 ( these are all still for each side,) and 134 feet per side for 160 meters.  You can figure these better for the area of the band you like best. If I remember right the formula is 468/ f (in mhz)..and cut long and trim.

  Connect all of one side to the center conductor of your coax, and the other side to the shield.  Make sure this connection is watertight so rain doesn't get in and soak your coak..( then ya have to fix it.)

You put the center up as high as you can and run these either with the top wire (longest one )straight and the rest hanging below each other using spacers, or I prefer to run them like  inverted V's and set each pair to a different compass point.  If you were to look down from the top they would fan out like radials on a clock or a star or what ever.  There is very little interaction when you do it this way.  

This way you have one feed line, an antenna for each band and need no tuner, and depending on the frequency, you cover different areas of the world, as they are pointing in different directions.

This works  because lets say you send a 40 meter signal up the coax, it sees the 40 meter wire as real inviting and the rest look like high impeadence things it doesn't like, so it takes the easy one and goes out on the 40 meter wire. Just like us, RF is lazy and always takes the easy way.

I reccommend you put a good ground in the earth for your station, and put a lightning arrester on the coax.  I also like to use a counterpoise with this ( and basically with all setups!!) setup, which is nothing more than a 1/4 wave wire for each freq, attached to the ground post on the radio. ( I like to use rotor wire for these, easy to cut, and easy to run). This moves any stray rf out to the other end of the counterpoise, and supposedly make the antenna work better too.

Unless you put this up real high, it will be almost omnidirectional on 160 m , 80 m, and possibly 40 m too. you have to get it up like a 1/2 wave length for it to start to put out the lobes you see on a Smith chart..

Any how I hope this helps. I have used this antenna several times and really find it quite adequate, better than most verticles, and on par with some 2 element beams too...it really works..


73  tom N6AJR    ( and please excuse the typing.. my one finger is tired..Smiley

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KF4ZGZ
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Posts: 277


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« Reply #6 on: October 08, 2001, 07:07:13 AM »

Good Question! And one that will get a lot of reading and good answers.
 Now for the good stuff. If you want all around preformance you will have to live with a bit of compromise. First , feed your dipole with ladderline and a tuner. Ladderline is all I use on hf. This makes multibanding much easier. I would suggest a slightly modified "G5RV". What you will actually have is a center fed zepp. 130 ft. ( 65 each side) seems to work on 80m-10m well. Some say it will work on 160m ,but I had a horrible amount of in-shack rf. OUCH! The problem with feeding with coax is that impedences will be way off and hamper use on some bands.Also line loss will be a problem. The problem with going with much longer than 130 ft. is 10-15m performance. I have a 160m bent dipole that's great for 160 , but lousy once you get past 20m. If you want to go with a longer antenna, I would suggest that you consider putting up a separate 20-10m dipole. If you want to use the coax, go with the "fan" dipole in the N6AJR post.
73 es good luck de Matt, KF4ZGZ
ps-If you want info on a 160m dipole with a 80m size, email me.
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WB2WIK
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Posts: 20545




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« Reply #7 on: October 08, 2001, 01:45:56 PM »

If you have a wooded 1/2-acre and want a wire antenna, I'd not recommend any of the three listed, but opt for a horizontal loop instead.

As I've stated here before (do a search for "loop antennas" and you'll find many applicable threads), the loop antenna is probably the best use for a piece of wire since the piano was invented.

A resonant loop, like one 260' or 520' in perimeter and formed in the shape of a horizontal square, can be fed with ladder line and used on all bands effectively, using a tuner having BALANCED line outputs in the shack.  Many proclaim similar success simply using a 4:1 balun at the loop feedpoint, and coaxial cable to the shack, permitting use of the autotuner in your transceiver, in lieu of a balanced line tuner which would be outboard.

A horizontal loop installed 35-40' above ground is an amazing system that costs perhaps $20-$40 to install and will very likely outperform any of the commercially packaged wire antennas you listed.

73 de Steve WB2WIK/6

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W0FM
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Posts: 2052




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« Reply #8 on: October 10, 2001, 01:58:25 PM »

If I could, I'd do what Steve suggested and put up a large loop.  CCR's from both the neighborhood association and the XYL make that approach prohibitive at my QTH.  I have, however, experienced great results with an Alpha-Delta DX-EE (same antenna you are considering, less 80M) in my attic.  I'm able to work all the DX-peditions with the DX-EE and 100 watts.  It is easy to put up and tune and gives me multi-band operation with a single feed point.  I feed it with 9913 and a 6-loop coax "balun" at the feed point.  No magic here, and, certainly, not the best of antenna setups.  But, it has been an effective compromise.  Good luck!  Terry, WØFM    
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WA9KZY
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Posts: 8




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« Reply #9 on: October 21, 2001, 11:08:38 AM »

Here is an excellent article from the AntennEx site. Hope they don't mind.

GL,
Warren


What Sould Be My First Antenna?
By Richard Morrow, K5CNF
Which antenna is the best for a new ham to put up? That is a hard decision to make, because a lot is going to depend on what you have for space. Also, height restrictions might have a bearing on what you string up. If you are going to put up a tower, this article is not for you. Here we will talk about simple basic antennas, such as the dipole and its various configurations, verticals, and wires like the Windom and the Zepp, so called because it was used on Zeppelin air ships, such as the Hindenburg.

To start off, the dipole is the easiest to construct, since all that is needed is two pieces of wire each 1/4 wave long, a center insulator, and either 50 or 72 ohm coax or twinlead depending on how low you want your swr to be. The impedance of a half wave dipole fed in the center is 72 ohms, but it works fine with 52 ohm coax. An inverted v dipole, where the center is higher than the ends, has an impedance that will vary around 50 ohms, depending on the heights of the ends in relation to the center and the center height above ground. A folded dipole has an impedance of 300 ohms, and can be made out of and fed with 300 ohm TV type twinlead.

The dipole is a good antenna and a lot of DX has been worked with just a dipole and low power. The pattern is a figure eight broadside to the antenna. In other words, at right angles to the direction the antenna is hung. A dipole that is running north and south has the main lobes going east and west. With this in mind, it is possible to aim your signal in a given direction. Indeed, dipoles have been made that rotate on the higher bands for just this reason. Since the dipole is bi-directional it only needs to be rotated 90 degrees. There are a lot of dipoles up in the world because they do the job.

The other popular version of the dipole is the inverted V, so-called because it looks like a V since the center is higher than the ends. The resonant frequency can be changed by raising and lowering the ends, but it is easier to just set it and forget it. The higher the center, the better it gets out, also the higher the ends are, the better it works. The inverted V tends to be more omni-directional than a regular dipole, as the pattern tends to spread out along the line that the antenna is running.

An interesting thing about the inverted V is you can alter the feed point impedance by altering the angle of the legs. However, that changes the resonant frequency of the antenna and the length of the legs has to be changed. The resonant frequency also changes if the height of the center is changed. So, all of this must be kept in mind when dealing with changes made to the antenna.

It is also a good idea to use a balun at the center of the inverted V or any dipole if you are feeding it with coax to make the transition from an unbalanced feed lint to a balanced antenna. This will pretty much stop stray rf currents from flowing down the feedline to cause TVI, and other nasty things from happening. It will also help to maintain a balanced figure 8 pattern from either the dipole or the inverted V. Of course if you are using open line or twinlead you don't have to worry about this transition since these feed lines are balanced.

It is just as important to keep in mind that tuning of the antenna is as important as tuning up the kilowatt final. It is not too hard to get your antenna up, just time consuming. Most people use an swr bridge to resonate their antenna. BUT, there is a better instrument to do this with and that is an antenna bridge, several of which are on the market. The reason a antenna bridge is better than an swr indicator is that unless you have the swr bridge at the center of the antenna, your feedline can and will influence your readings. The way to avoid this is to have the feedline an electrical 1/2 wavelength long or a multiple thereof. The reason for this is that a 1/2 wavelength reflects the impedance of whatever is connected to the opposite end. In other words, if you put a 90 ohm deposited carbon resistor on the end of a 1/2 wavelength long coax, you will measure 90 ohms plus the rf resistance of the coax with the rf bridge. An swr bridge will show some swr. Incidentally, the rf bridge will allow you to accurately measure rf electrical lengths. It is better to have a feedline that is an electrical 1/2 wavelength than one of a different length due to the influence an odd length cable can have on your antenna tuning. It is better to coil up the extra coax and stow it somewhere. This will allow the antenna to also achieve maximum bandwidth.

At this point it would be appropriate to state that any sort of conducting object within 1/4 wavelength of the antenna is going to affect the tuning, impedance and pattern of your antenna. To be more specific, a chain link fence that runs broadside to a horizontal antenna is going to affect the tuning of the antenna a certain amount, as is a metal patio roof under the antenna. A vertical will be affected by vertical conducting objects the same way. If you are beginning to realize that everything in the immediate vicinity of an antenna can have an effect on its tuning, you are right. It is very important to get the antenna tuned up correctly for maximum efficiency, and your solid state transmitter will not shut down due to high swr. The old tube transmitters would tolerate mismatches more than the solid state rigs do, and a tube rig would spit fire and hiss and melt something, usually easily repairable if there was a severe mismatch in the antenna circuit.

The transistorized rigs shut themselves off or commit hari kiri if things are not just perfect. Either is not desirable, both result in no signal and one in great expense. So, let us continue down the road to better signals.

"I want to operate more than one band. How is that going to affect the antenna and feedline if I get my antenna tuned up on 80 meters and want to operate on 40 meters." Well, the antenna is going to become two half waves in phase, since each 1/4 wave element on 80 is going to be somewhere in the vicinity of 66 feet long and that is equal to 1/2 wave on 40. So, the total length of the 80 meter antenna will be equal to one wave length on 40. Since the antennas are fed at the center with equal amounts of power, the currents are going to be in phase. So you will get some gain from that antenna.

As for operating a forty-meter antenna on 15 meters, that will work fine, except the feedline will not come out at 1/2 wavelength. In this case, the feedline will come closer to 1 1/2 wave length which will be just fine if you using 1/2 wavelength on 40. The element lengths will come out close to 3/4 wave length. Again, there will be some gain as this antenna will act as a broadside array for the same reasons as mentioned for the 80/40 dipole. Twenty meters with a 40 meter antenna will work fine since the lengths work out the same as the 80/40 dipoles.

The patterns of the antennas operated in this manner will be strange and many lobes will pop up in different directions as bands are changed and that sure will make life interesting. You will need an antenna tuner for sure if you choose to operate in this manner, but it works and works well and it is cheap. An 80 meter dipole, fed with a 1/2 wavelength, can be used on all harmonic bands above its primary frequency range, but you must be able to tune out the reactance which calls for an antenna coupler of some sorts. The older Johnson Matchboxes were very adept at this type of operation, and excelled at multi-banding a twinlead fed dipole or inverted V.

Another variation on the dipole consisted of two inverted V antennas with their centers at the same point and one fed 180 degrees out of phase from the other. This gives an omni-directional pattern, depending on what is surrounding your antenna, and a low angle of radiation, which is fine for DX. Keep in mind the dipole has been around a long time and will be around for as long as there is some one to use it.

The next antenna many absolutely detest is the vertical. But, the vertical has a lot going for it. It is usually unobtrusive, has a low angle of radiation and easy to put up. A vertical usually is not as good as a dipole for contacts close up due to the angle of radiation being so low. But, they can lay down a good signal at a DX location. If several are used in a phased array, you can just about switch directions nearly instantly. For the low bands 160/80/40, the use of phased vertical arrays is the only practical way to get any gain on these bands without spending a huge amount of money for towers and rotary arrays. Maintenance is easier and phased arrays don't catch the eye or airplanes as much as a 80 meter 3 element yagi.

Vertical antennas come in several sizes that work well. First is the 1/4 wave, which is the most common found on the ham bands. Verticals of this type DO require a ground system of radials, and it would help to resonate the entire ground system with a series tuned circuit. Most hams string out as many radials as they can, not always in a straight line, but the more the merrier. A ground rod at the end of each radial is nice, but expensive.

There has been several articles written on verticals and at least two or more books on amateur vertical antennas. One fellow wrote an excellent article on maximizing radial lengths. Basically, he said that 1/8 wavelength radials had more current in the system than an equal system of 1/4 wavelength radials. So, there is room for experimentation there, if any one wants to pursue it further.

There are several types of vertical antennas that do not need a ground system and one of them is the vertical dipole. A vertical dipole is just what the name says, a dipole hung vertically. The impedance does not change and the antenna becomes omni-directional. The feedline needs to be kept at right angles to the antenna for at least 1/4-1/2 wavelength to minimize rf coupling back into the feedline. But, this is true about any antenna. It is most practical at frequencies above 20 meters due to the size of anything for the lower frequency bands. This type of vertical can be phased just like the 1/4 wave vertical and it will work just fine as a directional array.

The other non-radial vertical is the 1/2 wave vertical. This type of vertical has a very low angle of radiation, and is an excellent DX antenna. Again, the size of the antenna is limited by the frequency used. The Cushcraft R3 is an example of a 1/2 wave trap vertical and it is remote tuned for 20, 15, and 10 meters. It is only 6.7 meters (22 ft) tall and is self-supporting. A 1/2 wave vertical could be made for any band with proper loading techniques. By a combination of center and top loading, a 160 meter version could be put up. The 1/2 wave vertical does need a matching network since it is being fed at a high-impedance feed point. It does have the advantage of getting the major current node above the surrounding ground level objects, which will increase your radiated signal and cause the radiation pattern to be less distorted by the presence of objects in the immediate antenna field.

The vertical antenna does seem to be more prone to certain types of noise than a horizontal antenna and you should keep this in mind. Also, a vertical needs to have a static bleed-off rf choke at the base connected to the ground system to keep the static electricity from building up.

The single-wire antennas are the simplest ones to put up, and will do a good job, as long as you are willing to live with the shortcomings of this type antenna. This antenna needs to have a good ground and some sort of antenna matching unit. If you do not use a good ground, you will get rf all over the place and burns will be common place. So will TVI and the goodwill between your neighbors will vanish rapidly. An antenna coupler will be needed to match the varying impedance of the wire antenna to the transmitter as you change frequency. It is better to have the antenna where you can feed it with coax to an antenna coupler out of the shack and remote tune it. This will keep the rf out of the shack and off of the rig. That may not be possible, so take whatever precautions you can to keep the fire off of the rig and in the antenna.

Be sure all of your equipment is grounded together by a ground strap and then grounded by the shortest possible lead to a good rf ground. An end fed 1/2 wave antenna is being fed at a high voltage point. So, be prepared to deal with that in your shack if you just poke it into a coupler on the top of the transceiver. If you feed a 1/2 wave antenna though a coupler of some sort and use a balanced feedline of 1/4 wavelength with only one side hooked to the 1/2 wave radiator, then you have a ZEPP antenna. There will be some rf in the shack and some radiation from the feedline. It can be used as an all-band antenna, but you will get rf in the shack on some of the bands.

A 1/4 wave wire can usually work fine just plugged into a coax connector on the back of the rig, since the impedance is usually close enough to work fine without any matching network, but one would be advisable, just in case. A good ground is definitely required in any case. Keep in mind having the end of an antenna come into the shack can cause a problem due to inductive coupling into the house wiring with all of the various problems rf can cause when it gets into solid state ac powered devices. It might not be worth it to use this one unless you are operating portable somewhere, for a very short time.

The random length wire is one the antenna putter-upper person forgot to measure. This wire antenna definitely needs a coupler, as the impedance will vary drastically from band to band. Again, a good ground is definitely needed for this antenna to work against.

A counterpoise is another thing you can use with long wire and other antennas. The counterpoise is a wire or several wires, equal to but not less if you can manage it, that is mounted close to the ground, but insulated from it to increase the capacity to ground through a low impedance capacitive coupling to ground. It is not meant to replace a stations ground system, but to supplement a poor rf ground. A counterpoise also can lower the radiation angle over a poor ground of a wire antenna. It can be used with any antenna.

Now that you have had a look at the basic antennas out there, the next thing is to figure out what type of operating you want to do. Ragchew with the guys on 7.213 MHz over about a 600-800 mile radius in the daytime, chase DX on the lower end of 40 meters at night, chase the DX on 20/15/10 meters with QRP, operate traffic nets on 75 meters at night, or whatever. Only you know what you enjoy doing and the choice of the correct antenna can make the difference between enjoying your hamming and being miserable.

Keep in mind the lower you hang a wire the higher the angle of radiation and the stronger your signal will be close in on the lower bands, because the sky-wave will come down closer to where the ground wave poops out.

160 meters is in a class by itself, and antennas get rather LARGE, but it is the only true mf band we have. It is a fun band though. For the most part the vertical is not too good for close in communications unless you are on 160 since its ground wave extends further out than the other bands. Get your antenna up as high and in the clear as best you can and just see what you can work.

Remember these facts of antennas:

1. A poor antenna is better than no antenna.

2. An antenna that works well for you might not work for someone else due to many variables, some known and some not.

3. You will never know how well an antenna works until you try it.

4. Never condemn an antenna unless you fully understand why it did not work.

5. Choose an antenna appropriate for what you plan to do. A rhombic is not a good choice to work stations within a 300-mile circle of you.

6. Research your requirements as thoroughly as you can.

7. Do not put up more than you can afford to have blown down more than once a year. It WILL happen one day!

8. Make your antenna choice based on your situation and operating requirements, not someone else's.

9. Antenna height increases as the square of the severity of the lightning storm.

10. Antenna height decreases with the rarity of the DX station and how bad you need it for DXCC.

11. Subscribe to antenneX, you need this vital information for reference.

It is important to remember there are so many variations of the antennas mentioned here. Far more than can be listed in this brief article. There is room for experimentation. There are numerous books and back issues of the ham magazines that explore many of the possibilities. After all, antennas are not too expensive unless you are into huge towers and a rotating aluminum overcast. The average ham can experiment with wire antennas forever. Just keep notes and accurate records for future reference such as photographs and a article in antenneX. Test equipment doesn't have to be expensive. A noise bridge and a wattmeter or vswr bridge and lots of reference books will make it interesting.

Remember, antennas are the cheapest thing you can use to increase your signal strength, both on transmit and receive. If you are unable to put up a tower and beam for 20-10 meters, a phased array of some sorts could be the solution, either vertical or horizontal. Phased arrays have a lot to offer, as a vertical array can change direction as fast as the relays can switch, and there is no rotor or tower to worry about, which is nice. Horizontal arrays can be rotated, and one like the W8JK array can cover 20-10 meters if it is fed with twinlead and a tuner, with no traps. It only has two elements and is bi-directional, but it does work well and has been around for many years. There are a lot of other antennas that have been around for years and work very well. Some work better than some of the newer ones, but they were lost in the shuffle down through the years. So do your research thoroughly, and experiment! It is the way to knowledge.
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