• Antennas don’t really have gain in the same way that an amplifier has gain. When you use a linear amplifier, you get more power out than you put in. Since transmitting antennas are passive devices, there’s no way to get more power out than you put in.
• It’s not easy to measure antenna gain. There is no antenna gain meter that you can simply hook up to an antenna to measure its gain.

So, what is antenna gain? According to question E9A08, antenna gain is the ratio relating the radiated signal strength of an antenna in the direction of maximum radiation to that of a reference antenna. What this means is that when you talk about antenna gain, you have to know what kind of antenna you’re comparing it to.

When talking about antenna gain, antenna engineers often refer to the “isotropic antenna.” An  isotropic antenna is a theoretical antenna used as a reference for antenna gain. (E9A01) An isotropic antenna is an antenna that has no gain in any direction. (E9A03) That is to say it radiates the power input to it equally well in all directions.

Let’s take a look at a practical example. I often say that the 1/2-wavelength dipole antenna is the most basic amateur radio antenna. Well, the dipole actually has some gain over isotropic antenna. The reason for this is that it is directional. The signal strength transmitted broadside to the antenna will be greater than the signal strength transmitted off the ends of the antenna.

The gain of a 1/2-wavelength dipole in free space have compared to an isotropic antenna is 2.15 dB. (E9A02) Sometimes, you’ll see this value as 2.15 dBi, where dBi denotes that  and isotropic antenna is being used for this comparison.

Since the isotropic antenna is a theoretical antenna, some think it’s better to compare an antenna to a dipole antenna. An antenna will have a gain 3.85 dB compared to a 1/2-wavelength dipole when it has 6 dB gain over an isotropic antenna. (E9A13) You obtain this value by simply subtracting 2.15 dB from the 6 dB figure:

Gain over  a dipole = gain over an isotropic antenna – 2.15 dB =
6 dBi – 2.15 dBi = 3.85 dBd

Sometimes, the gain over a dipole is denoted as dBd.

Similarly, an antenna has a gain of 9.85 dB compared to a 1/2-wavelength dipole when it has 12 dB gain over an isotropic antenna. (E9A14):

Gain over  a dipole = gain over an isotropic antenna – 2.15 dB =
12 dBi – 2.15 dBi  = 9.85 dBd

I used two lengths of PVC pipe to form the horizontal elements of this simple, 10m loop antenna.

It takes me forever to complete some projects. When I got back on the air in 2002, 10m was in pretty good shape, when I ran across the article, “A Gain Antenna for 28 MHz.” It seemed simple enough to build, and I even went so far as to purchase and cut to length two pieces of PVC pipe to support the antenna. Well, time went by, and I never got around to finishing the antenna before the sunspot cycle went south on me.

This sunspot cycle has been notably lackluster, at least up until about a month or so ago. The ten-meter band was rarely open, so I wasn’t really motivated to finish and put up this antenna.

About a month ago, though, noting the more frequent band openings, I finally decided to finish the antenna. I cut the wire and attached it to a Budwig center insulator.  Then, I left it laying on the floor of my shack.

Well, today, with the temperatures in the 40s, was the perfect day to get it in the air. I flung a tennis ball over a tree branch in my backyard and hauled it up.  I’m finally on 10m with an antenna that should work better than my 30m dipole!

The SWR is 1:1 down in the CW portion of the band and still only 1.5:1 at 28.500 MHz. Not bad, I’d say.

Unfortunately, there wasn’t a whole lot of activity on this afternoon around 3:00 pm when I finally got it in the air. I did manage to work HH2/HB9AMO, though, and a station in UT and one in the Virgin Islands heard me calling CQ and reported as such on ReverseBeacon.Net. Bring on the skip!

The second is an online antenna tuner simulator that appeared in the September QST. By playing with it, you can see how changing the settings of the tuner affect the values of the capacitors and inductor and how eventually you get to a matching condition.

It would be interesting to have such simulators for various other matching networks, such as the L-network for matching random wires and for the matching network used to match end-fed, half-wave antennas.

What do most hams think about? For most hams, an end-fed antenna is and “end-fed, half-wave,” or EFHW, antenna. That is to say that the antenna is the same length as a half-wave dipole antenna. When the feedline is connected to the center of a half-wave antenna, the feedpoint impedance is theoretically 72 ohms, which is a good match to both 50-ohm and 70-ohm coax and the 50-ohm outputs of most ham transceivers.

The ideal end-fed, half-wave antenna. (from AA5TB.Com)

When the feedline is connected to the end of a half-wave antenna, the situation is quite different. At the ends, the impedance is thousands of ohms. To connect a feedline there, you need some kind of matching device. This matching device transforms the impedance from 4,000 or 5,000 ohms down to 50 ohms.

If the impedance is so high, why would you want to use an end-fed, half-wave antenna? Well, for one thing, it’s sometimes easier to connect a feedline to the end of an antenna instead of the middle. It also makes the feedline much shorter.

With that in mind, here are some links to other resources on EFHW antennas:

• LnR Precision. LnR now sells the Par EndFedz line of antennas. These are hundreds, if not thousands, of these antennas out there, and I’ve never really heard anything bad about them.
• AA5TB.Com. AA5TB has a bunch of pages on the EFHW antenna, most notably articles on different couplers and an article on the basics of the EFHW antenna. He’s also posted a spreadsheet to help you design your own EFHW tuner.
• KC8AON’s 40 – 12 m EFHW Tuner. Most EFHW couplers are for a single band. This QRP coupler can be used with half-wave wires from 40 m through 12 m.

I plan to use a QSO-King end-fed antenna with my new Kenwood TS-590. Does anyone have any experience with this antenna? I’ve read good reviews from many people.

I chose this antenna for several reasons. The biggest is that I lease my house and this will have the least physical impact on the house. It will also be relatively unassuming. I will string this between two telescoping antenna masts that I can stick in the ground and attach to each side of the house.

Well, after taking a look at that antenna, I replied:

I’m not so sure that I’d believe all the claims that he makes for this antenna, but you should be able to make some contacts with it.  Most end-fed antennas are single-banders with a matching network that provides a match to 50 ohms on that band. This guy’s just using a balun to bring down the SWR to something that your rig’s internal tuner can match.

Instead of spending 70 bucks on this thing, why not buy some ladder line and antenna wire and make your own end-fed Zepp antenna?  Google “end-fed zepp” for plans. Using ladder line will be a lot more efficient than using coax.

The “QSO King” is an end-fed antenna, but it’s not an end-fed, half-wave (EFHW) antenna that most us think about when we hear the term “end-fed.” I’m not even sure what you’d call this antenna, except maybe an end-fed random wire, with a balun connected to it to try to bring the SWR down to something than a rig’s internal tuner can match.

Another ham, who’s noted for more caustic remarks than I usually make wrote, [The antenna's Web page] “cleverly interlaces demonstrable facts (like the voltage withstand of Thermaleze wire and waterproof enclosure) with subjective and anecdotal statements of performance. No where in his ad does he state any measurable performance parameter.”

In response to the statement in the ad, ”Important Note : The antenna works best if the coax is at least 33-ft. long,” this same guy wrote, “Warning, Will Robinson! Beware the design that requires a specific feedline length. It can only mean it’s radiating, or it’s ballast.”

Finally, he advises, “If all you’re looking to do is run a tuner-fed random wire with or without a radial or counterpoise, just run the wire, jack it into the tuner and be done with it. No point in sending this guy money just to get the same (or worse) result.” Amen.

This second one is really incredible. If you’ve ever worked any of the DX contests, chances are you’ve worked OH8X. It’s a monster contest club. One of their towers is a 100m (330-ft.) monster that holds a three-element Yagi for 160m and a five-element Yagi for 80m. But, ham radio is not all they use the tower for. Watch below:

I have been reading both the ARRL Antenna Book and their Wire Antennas book. It is staggering the different types of antenna designs that are out there. Some I have never seen or even heard discussed.

What amazes me is that in addition to the sheer variety of designs, many  of these antennas were first designed in the 1920s. There isn’t much technology out there today that is just a relevant today as it was almost one hundred years ago.

I replied:

Well, I wouldn’t be too sure about that. I think it’s just that we take that technology for granted. Think really basic things like nuts and bolts, levers, basic metallurgy, etc. Antennas are similar.  It’s basic physics that dictate their design and use.

What do you think?

Now, I’m not sure exactly where this bit of advice comes from and what the theory is behind it. Can anyone point me towards a discussion of why this is so?

After having said all this, I got an e-mail from my Elmeree this afternoon. He asked, “So, which is better for a vertical antenna, a solid rod or a tube?”

My answer, “Whichever material you have on hand or whichever is cheaper.”

Some of the comment are great, too. Read the entire story here.