Can't Stop The Signal - Aerials at N3OYA

One of the most satisfying things about amateur radio is making your own communications gear. With modern technology becoming ever more miniaturized, making a state-of-the art radio is next to impossible, so we're restricted to rolling our own accessories. That's still something.

My area of "homebrew" joy is antennas. All of the antennas at N3OYA are made by N3OYA, and here you'll find the complete rundown of them. You'll also be able to read my findings -- whether or not it's a good design, etc. -- as well as construction notes and the benefit of my experience (read: "soldering burns").

I have concentrated on aerial designs which do not require matching wizardry in order to bring the feedpoint impedance to 50 ohms. There are a couple of antennas here which require the addition of a matching device of some sort, but precious few.

We'll go from top to bottom.

VHF/UHF

Hentenna

http://www.qsl.net/wa0itp/

http://homepage3.nifty.com/lzk/ANT3.html#Hentenna

The "Hentenna" was developed by Japanese amateurs JE1DEU, JH1FCZ, and JH1YST in the 1970s. It is impressively simple and inexpensive to make, simple to deploy, and possible to match perfectly to 50 ohms. It can be oriented for either vertical or horiztontal radiation, which makes it versatile for multi-mode operations. It also enjoys more than 3dB of gain over a dipole, and is directional in two dimensions, just like a dipole. All these characteristics make it a perfect antenna for the beginner or experienced amateur alike.

Moxon "beam"

http://www.qsl.net/ac6la/moxgen.html

http://www.cebik.com/moxon/moxpage.html

This antenna design is entirely due to the work of Les Moxon, G6XN, who modified a design by VK2ABQ. The original antenna was basically a square loop turned from the vertical to the horizontal planes. The wire was cut on the sides not containing the feedpoint or opposite to it, thus creating a kind of folded two-element beam antenna.

Moxon lengthened the front and rear elements and shortened the side tails. It provides a close -- and often perfect -- match to 50 ohms, as well as a very nice radiation pattern with minimal side lobes and lots of front-to-back gain. Forward gain is somewhat sacrificed.

But I've never thought it wise to design an antenna for massive amounts of forward or F/B gains, then have to mess about with bringing the feedpoint impedance into line with matching techniques. Antenna gurus such as W1FB contend -- rightly -- that one is better off sacrificing a bit of gain in order to keep the radiation resistance and feedpoint impedance within optimum values. Any matching network or device merely brings the impedance of the antenna system into line with what our modern transceivers like to see: 50 ohms. The feedpoint impedance might still be on the order of 15-28 ohms, even if the transmitter sees 50 ohms. That's loss at work, and we must avoid it.

Direct-Connect Beam(s)

http://www.clarc.org/Articles/uhf.htm

Usually Yagi-Uda antennas exhibit low feedpoint impedance, and require quite a bit of fiddling with matching networks in order to bring the radiation resistance into line. These designs avoid that, albeit with the sacrifice of a bit of gain. Plus, neither of them cost terribly much to make!

The Tiny-3 comes from http://www.qsl.net/w4sat/tiny3.htm. It's easy as pie to make (and probably about as expensive), effortless to tune, and a great investment of an afternoon. That's all it took me to make the thing, and I have no doubt yours will be just as simple. Plus, you can get everything but the 50-ohm coax from one of the big box DIY home improvement centers.

The 3-element Yagi found at http://www.arrl.org/tis/info/pdf/9304054.pdf is just as simple to make, though it uses a more complicated matching assembly. Again, one afternoon will have you on the air, and you can get everything but the coax from a DIY center.

The least expensive -- and probably the most versatile design -- comes from http://www.clarc.org/Articles/uhf.htm. I made mine from 0.25" copper tubing in the space of an afternoon. Hint: since the antenna is designed for the lowest end of the 2M band, make the driven element a bit longer, so as to get good coverage over the entire band.

Verticals Et Al.

I've tried bunches and bunches of vertical VHF antennas over the years. They're a good idea, especially if you live in an area where you have easy access to a bunch of different repeaters or a bunch of amateurs for direct signalling. They're good for general communications because they're omnidirectional, can have decent gain, and can be simple to make. I'll list a few.

The J-pole

There are scads of J-pole antenna designs out there, of varying worth. At the bottom of the list is, in my opinion, the "roll-up" j-pole, constructed of 450-ohm ladder line or 300-ohm twinlead. They're a pain to tune, they're fragile, and you have to put them inside a tube if you want to mount them outside in a permanent installation (which defeats the purpose, but that's another thing entirely).

A simple 1/2-wave antenna will provide gain over a 1/4-wave. And that's easy to make for 2M out of copper pipe in a classic j-pole. I'd give you all the measurements and such, but that's not enough of a challenge!

Here's what it should look like. Use the formulae to find the approriate dimensions for your frequency of choice (yes, it will work on other bands than 2M):

(pic from Jaden's tutorial)

High Frequency Antennas

Antennas Under Development

http://members.tripod.com/~KE4UYP/80m_160m_Antenna.html

Loops?

Already Made/Used

 I've made and used all sorts of wire antennas for HF, and used them from several different locations, none of which had even sufficient antenna space (much less "lots").  But that didn't stop me!

G5RV - http://www.cebik.com/wire/g5rv.html

 I have made and used several different G5RV antenna systems over the years. For those unfamiliar with the device, the "G5RV" was developed as an antenna system by a UK amateur (Louis Varney, G5RV) some years ago. It was designed and optimized for 14.15 MHz as a 3/2-wave antenna with a 1/2-wave matching stub comprised of homemade 525-ohm open parallel feeders. This matching stub is then affixed to a 70-75-ohm coaxial cable, the length of which is immaterial.

 It is commonly held -- and advertised by commercial antenna-makers -- that the G5RV is an all-band antenna, that you can hang it any which way, install it as an inverted-vee, and use it without the benefit of an "antenna tuner"; in other words, that it is the cure to all HF wire antenna ills. This is not necessarily untrue. It is, however, very much misleading.

The G5RV is intended as a gain-bearing antenna system for one resonant frequency, and even the designer used a tuner/transmatch to bring SWR down. At frequencies other than that for which it was designed, it works, after a fashion. A transmatch must be used to bring the system's impedance into a range in which it might squeak out a signal.

 It is also true that one can load up any center-fed doublet with enough extra inductance and capacitance and bring the system into line. Keep in mind that by using your transmatch you're not bring the antenna system into resonance. That is physically impossible. You're merely making your transmitter "see" 50 ohms or something close to it; in other words, you're lowering SWR. It's still a non-resonant antenna system.

 In fact, your losses will likely be such that you're barely putting out any signal at all, especially in the case of the G5RV: Since there's coax between the transmitter and the antenna, most of the standing waves will be in the coax.

There is another factor: Ground. As with any horiztonal, doublet-type antenna, the G5RV works best when it's installed at least one wavelength above ground at its design operating frequecy (in this case, 20 meters). While there is a seemingly-desirable resistance and reactance dip at a half-wavelength (10 meters), the radiation pattern is degraded. Even if one can install the system at that height, it is still too low for good results on lower (tuneable) frequencies.

Now that I've pounded the G5RV into the ground, let me make a rather abrupt turn. The G5RV works, and works well, for some amateurs. Some amateurs, contrained by small lots, have the choice of using a compromise horizontal antenna (like the G5RV) or a multiband vertical. In my opinion, multiband trapped verticals are to be avoided at all costs above 10 MHz, so maybe installing a G5RV -- inverted-vee or flattop -- is your only choice. I'd argue against it, though. You're far better off with...

Center-Fed Doublet Fed With Balanced Wire

This antenna was, when I had one installed, as long as could be reasonably installed. This was a total of 90 feet across the top, fed  through a transmatch with 450-ohm ladderline.  I managed to get it to work on every single HF band with 100 watts and an SWR below 2:1.  The only band which gave me problems was 40M, but that was because I had a very, very bad station-grounding problem on that band (the station was on the second floor).  I never did model that antenna, unfortunately; I'm sure the radiation pattern was rather interesting.

Like all wire antennas, the open-line-fed doublet must be installed as high as is possible.  Mine was up a good 50 feet.  Also remember that open-wire or ladderline must not twist or touch metal things, or detuning will happen.

160/80/40 coax-trap vertical

This antenna was based on a QST article I got from the ARRL website (found here).  Since I lacked the linear space to stretch this in a dipole, I decided to make a vertical (out was out, but there was a convenient tree that said up was in!). 

Didn't have lots of linear space for radials, either, but I did what I could by driving three ground rods and affixing five 65-foot radials to them.  I ran the radials as close as I could to straight out from the base of the radiator, but the lot was too narrow.  So I kind of zig-zagged them to fit the available space and hoped for the best.  It worked, and worked well! 

My lack of a good receive antenna (and low power) meant that I didn't do much work on 160M, but it gave me good reports on 80 and 40M SSB contacts.

"Longwire"

This last antenna is probably misnamed, because a true longwire antenna is more than one wavelength on the fundamental frequency.  Thus a 40M longwire must be at least 40M long.  Mine was probably 50M long, but I used it on 75/80M, too.  It ran through a window to a tree; the tree end was about 60 feet up.

In retrospect, my installation of this antenna was, shall we say, optimistic.  This was in the second-floor station with the bad ground.  Longwires require a good station ground in order to function well. 

It worked out all right on most frequencies, but 40M was a total nightmare.  RF was everywhere.  Running more than 10 watts caused the worst kind of RF bite on every metal surface and sent my station computer into a tizzy.