How do you choose an antenna analyzer?

A reader recently e-mailed me:

In the past you told me you started with the Autek RF-1, and later moved to the Palstar ZM-30. I am finally getting around to thinking about purchasing an antenna analyzer, but I am stumped by the choices. In order of increasing purchase price this is what I’ve turned up:

How does one decide? Where does one go to find out the differences? Other than asking a fellow ham, how does one find out which one is the best antenna analyzer without paying an arm and a leg (unless the feature(s) so purchased are deemed worth the cost)?

Thanks! 73

He actually missed several other good choices:

  • Autek VA1 – $199. This is actually the antenna analyzer that I first purchased.
  • MFJ 259B - $240. This is arguably the most popular antenna analyzer on the market. MFJ has several other models with different feature sets.
  • YouKits FG-01 – $250. This is a very cute, little analyzer with a small graphical display. It seems kind of expensive, but the graphical display might be worth it.
  • Comet CAA500 – $450.

So, how do you choose just one from this list? Well, I think the first thing that you have to ask yourself is how you’re going to use the analyzer. If all you’re going to do is to check the SWR of your HF dipoles, then buy the Autek RF-1. It’s the least expensive unit, is reasonably accurate, and is small and lightweight, making it easy to use outside where your antennas are located.

Autek RF-1

The Autek RF-1 is inexpensive, and its small size makes it easy to use outdoors where your antennas are.

If you want to do some more serious frequency analysis, then you should be looking at the W4RT miniVNA or, if you have more cash, the Timewave TZ-900s. These instruments can help you do a lot more in-depth analysis of your antenna system. The figure below, for example, shows a plot generated by the miniVNA software. It shows the SWR of a multi-band vertical antenna from 3 – 33 MHz.

miniVNa display

For more sophisticated frequency analysis, consider the miniVNA. It uses a computer to generate graphs like this.

Some antenna analyzers do more than just SWR. For example, what sold me first on the Autek VA1 and then on the Palstar was that they also measured reactance. So, you can use the antenna analyzer as an LC meter as well. Palstar also says that you can use the ZM-3 as a low-level signal source.

Next, you need to consider what bands you’ll be using it on. Many antenna analyzers only cover the HF bands. That’s a bummer if you like operating 6m, or like to experiment with VHF/UHF antennas. A friend of mine bought the Palstar antenna analyzer after talking to the company at Dayton. At the time, they said that they were planning to come out with a model that covered 6m, as well as the HF bands.

Unfortunately, they never did come out with a 6m version, and he was sorely disappointed. He ended up buying a miniVNA instead.

Asking your fellow hams about the antenna analyzers they have is actually a good way to figure out what’s best for you. If you ask nicely, they might even let you borrow their analyzers or come over and show you how it works on your antennas.

Reading the reviews on eHam is also a good way to gather information before making a purchase like this. You certainly have to take the reviews there with a grain of salt, but if several reviewers mention a particularly good or particularly bad feature of a product, then it’s certainly something worth taking a hard look at.

If you’re new to the hobby, starting out small and working your way up might be a good strategy. You could buy one of the less expensive models and get used to how they work,  then sell it and make the leap to a more sophisticated unit. The way things are going, you should be able to sell your first antenna analyzer for at least 80% of what you paid for it.

Whatever you do, don’t fall victim to “paralysis by analysis.” Go ahead and buy one and start using it. This is a learn by doing hobby after all.

Choosing an HF vertical

Last week, an online amateur radio retailer contacted me about writing some blog posts for his website. One of the topics he suggested was “Choosing an HF vertical.” Here’s what I wrote this morning:

Choosing an HF vertical

For many amateur radio operators, a vertical antenna may be the only option they have to put up an HF antenna. They may, perhaps, live on a small lot, or they may not have suitable trees or other antenna supports from which they can hang dipoles.

Fortunately, there are many good products on the market. Unfortunately, there is some confusion about the different types of verticals out there. This short article will attempt to give you some guidance on how to choose the right vertical for you.

Trap verticals
Trap verticals have been around for a very long time. My very first HF antenna back in 1971 was a hy-gain 14AVQ. These verticals use “traps” that are parallel resonant circuits to electrically isolate portions of the antenna when transmitting on various bands. The traps make the antenna act as if it were a resonant quarter-wave vertical. For example, when the 14AVQ is being used on the 10m band only the lower portion of the antenna is active. When operating 40m, the entire length of the antenna is active.

Trap verticals need radials to operate effectively, and the more the merrier. Take this into consideration, when deciding whether or not to purchase a trap vertical.

No-radial verticals
In recent years, several manufacturers have introduced vertical antennas that do not need radials. GAP Antennas is one manufacturer that offers these kinds of antennas.

The manufacturers claim that these antennas are more efficient than trap verticals, and  many amateurs use them with good results. There are some drawbacks, however. They can be difficult to tune, and they do require mounting at some distance above ground. The reason for this is that they are, in effect, vertical dipoles and if the end of the antenna is too close to ground, capacitive coupling will detune the antenna.

Non-resonant vertical antennas
A third class of vertical antenna that is becoming popular is the non-resonant vertical antenna. An example of this type of antenna is the LDG S9v43 Vertical Antenna, although several other manufacturers also make this type of antenna.

One reason that this type of vertical antenna is becoming popular is that it can be used across a wide frequency range. The resonant frequency of this antenna is actually about 5.4 MHz. With an antenna tuner, however, you can use the antenna on all bands from 80m to 6m.

This tuner can be located in your shack, but for the lowest loss, you will want to locate the tuner near the base of your antenna. Don’t try using it with the internal tuner in your rig. On some frequencies, the antenna impedance will be quite high, and most internal rig auto tuners do not have adequate range to provide a 50-ohm match.

These antennas require radials. There is no formula to calculating the length of the   radials, but they should be at least 0.2 wavelength at the lowest frequency that you wish to operate.

We carry the entire line of LDG vertical antennas. The LDG S9v43 antenna is 43 ft. high and covers 80m – 6m, the LDG S9v31 antenna is 31 ft. high and covers 40m – 6m, and the LDG S9v18 antenna is 18 ft. high and covers 20m – 6m. All of these antennas use heavy-duty, telescoping fiberglass sections. The antenna is self-supporting, and because it’s very light weight, easy to install.

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I know it’s not a comprehensive guide to how to choose an antenna, but that’s not the intent. I also know that it’s a bit slanted towards the non-resonant vertical, but that’s the kind of antenna that the company carries.  Having said that, I’d love to hear your comments.

Ads of Note from the December 2012 QST

When I was a kid, I used to religiously pore over the ads in the Electronics Illustrated, Popular Electronics, and later on, QST issues that I received. I don’t do that every month nowadays, but I think it is a worthwhile exercise to do every two-three months. New products are always being introduced, and some of them can be quite useful and fun.

This month, I went through the ads in QST. Here are some that I highlighted.

  • Using Your Meter. This is a new book from The W5YI Group. It’s notable to me because I’ve been thinking that a simliar book might be my next publication. The No-Nonsense Guide to Using Your DMM—my working title—would be a lot cheaper than the $24.95 that W5YI is asking for this book, though.

    Got any tips for using a DMM? If so, e-mail me and I’ll include it in the book.

  • Bonito RadioJet 1102S. This is a software-defined receiver made in Germany and imported by a small company, Computer International, in Michigan. Unfortunately, the company’s website is a real disaster. I spent about ten minutes looking for a price for this radio without any luck.  So many small companies’ websites are so poor that I think it actually hurts, rather than helps their business.
  • MastrAnt. This company sells synthetic guy ropes. We’re going to need some of this down at the museum. I think the metal guy wires are detuning our 40m inverted Vee.

Do you peruse the ads in QST and other ham radio magazines? Which ones have you found interesting lately?

KB6NU finally builds an end-fed, half-wave antenna

I’ve posted about end-fed, half-wave antennas before, but until this weekend, I’d never built one. One of the reasons for this is that most designs are for QRP antennas and not made to handle more than 5 – 10 W of power.

A couple of months ago, I ran across a design rated at 100 W. The design seemed relatively simple to build, requiring only a single toroid and a capacitor made with a short length of RG-174 coax. Well, it just so happens that I bought 100-ft. of RG-174 at Dayton this year, and I found the toroid cores online from the  “Toroid King” for a very reasonable price, so I decided to make my own.

All told, the parts cost about $10, the biggest part of that the plastic junction box I got from Lowe’s for $6.41. Compare that with the $60 that LNR wants for their end-fed antenna.

Sunday was a beautiful day here with temperatures in the 60s, so I decided to put up the antenna. I’d love to report that everything worked perfectly, but this antenna is going to need a little more work. The SWR is 2.6:1 at 14.000 MHz, dropping to about 1.5:1 at 14.900 MHz.

Since the internal tuner on my IC-746PRO is supposed to be good to 3:1, I did use it and made a couple of contacts. The guy in MA even gave me a 599 signal report. I’d be a little more comfortable about using it, however, if I could get the SWR down a bit.

I e-mailed the guy who published the design and asked why he thought the resonant frequency was so high, and he said that all I had to do was add a couple feet of wire to the antenna. He also suggested that adding a turn or two to the coil would bring the SWR down. I did some more reading about end-feds and I’m thinking that perhaps adding a short counterpoise might be something to try, too.

So, while the results so far have been mixed, I’m hopeful that with a little tweaking, I’ll have another antenna to add to my arsenal. It’s been a good learning experience, and I’ve certainly saved a bunch of money over the commercial versions.

UPDATE 11/18/12:
I added 24-in. to the antenna  and it did indeed bring down the SWR of the antenna to below 2:1 in the CW portion of 20m.  I’m happier with this. I still do plan to try a counterpoise. Not so much to improve the SWR, but to see if it makes the antenna a little more efficient.

The box I used for this project is the Carlon E989NNJ, a 4-in. x 4-in. x 2-in. plastic junction box.  This is a very nice box. Not only is it completely enclosed. The screw down cover is gasketed, making it waterproof.

I liked the box so much, I went back to Lowe’s to get a couple more. Not only were they out of stock, when I searched their website for that part number, it came up with no results. It kind of looks to me as though they’re not planning to stack this box anymore.

I Googled the part number and found several places online that had them, but they wanted more money, plus I would have to pay shipping. Fortunately, I was able to find some at a local Home Depot. They wanted $6.88, compared to $6.41 at Lowe’s, but at least I was able to purchase a couple more of them.

Operating Notes – 11/1/12

ICOM/Kenwood Power ConnectorJunk, continued. A couple of months ago, I wrote about the importance of junk in amateur radio. Well, here’s another example.
Last week, my friend, Ralph, AA8RK, acquired a used TS-850. Unfortunately, it didn’t have a power cable, so he sent a message to our club e-mail list asking if anyone had a cable he could buy from them. It struck me that while I didn’t have a cable that I wanted to sell him, I did have all the parts needed to make one. For some reason a year or so ago, I happened to purchase the Molex connector at a hamfest, and at Dayton this year, I purchased more 12-ga., two-conductor wire and a big bag of PowerPole connectors.
Ralph came over Monday night, and we had a fine time making the connector and talking about ham radio in general. Ham radio is more fun if you have the right junk!

Horse-fence antenna revisited. One of the things that Ralph and I talked about was my horse-fence antenna. I was unsuccessful with my first attempt at making a 2m dipole with the horse-fence material and just haven’t had the motivation to get back to working on it. Well, when I showed it to Ralph, he said, “It looks to me like you have a bunch of little capacitors there,” referring to the 14 very fine stainless steel wires running through the plastic ribbon, “maybe that’s detuning it.”
I think he might be right.  I’m going to go get a couple more clamps and clamp the far end of the antenna elements and see what effect that has.

55th JOTAJamboree on the Air (JOTA) 2012. Almost two weeks ago now, we had a great Jamboree on the Air at WA2HOM. On Saturday, we had eight or ten Scouts. Several of them already had their General Class licenses, so all I had to do was sit them down at the radio, show them how to use the controls, and they were off to the races. They even worked a new country for us – Trinidad. The cool thing was that the station they contacted down there was also participating in the JOTA, and they got to talk to some Trinidadian Scouts.

 Sandy quiets the bands. On Tuesday night, the 40m band was oddly quiet as hurricane Sandy took out the power on the East Coast and otherwise occupied hams there. It was quite noticeable that there were a lot fewer stations on the air.

25, 50, and 75 Years Ago in QST

QST publishes a column every month towards the back of the magazine that highlights from issues 25, 50, and 75 years ago. Now that the QST archive is online, it’s really worth taking a look at these articles. Here are a few that were interesting to me this month:

  • October 1937
    • Modernizing the Simple Regenerative Receiver by Vernon Chambers, W1JEQ. This a nicely-designed and built regen using two tubes, a 6K5 pentode and 6C5 triode. I’m going to keep this design in mind if I ever get around to playing with all the tubes I have. As an aside, W1JEQ wrote 87 articles for QST from 1936 through February 1958. This was his third article.
    • Concentrated Directional Antennas for Transmission and Reception by John L. Reinartz, W1QP, and Burton T. Simpson, W8CPC. This article describes two different antennas. The first is a  half-wave loop antenna that the author says works on 2-1/2, 5, 10, and 20m. The second is a square loop antenna called a “signal squirter” for 14 Mc.
  • October 1962
    • In the “New Apparatus” item on page 27, a key made by J. A. Hills, W8FYO, of Dayton, OH is shown under the heading, “New Key Mechanism for Electronic Keyers.” The photo clearly shows a key whose design was adopted by whoever designed the Bencher BY-1 paddle.
    • The Towering Problem by Jay Kay Klein, WA2LII clearly shows that putting up towers have always been a problem for amateur radio operators. This is a humorous take on the problem. What’s notable is that this type of humorous article almost never appears in QST anymore. Amateur radio seems to have lost its sense of humor.
  • October 1987
    • Stalking Those Fugitive Components by Doug DeMaw, W1FB. We often complain about the demise of local parts suppliers, but this article shows that this was a problem 25 years ago as well. W1FB gives some advice that I gave not long ago–stock up on parts, especially when you find a good deal on them, and you won’t have to scrounge around for them when you want them.

Extra Class question of the day: Smith Chart

NOTE: This is the last installment of the Extra Class question of the day. I’m going to be compiling all of these into the No-Nonsense Extra Class Study Guide. Watch for it real soon now.

 

Figure E9-3A Smith chart is shown in Figure E9-3 above. (E9G05) It is a chart designed to solve transmission line problems graphically. While a complete discussion of the theory behind the Smith Chart is outside the scope of this study guide, a good discussion of the Smith Chart can be found on the ARRL website.

The coordinate system is used in a Smith chart is comprised of resistance circles and reactance arcs. (E9G02) Resistance and reactance are the two families of circles and arcs that make up a Smith chart. (E9G04)

The resistance axis is the only straight line shown on the Smith chart shown in Figure E9-3. (E9G07) Points on this axis are pure resistances. In practice, you want to position the chart so that 0 ohms is at the far left, while infinity is at the far right.

The arcs on a Smith chart represent points with constant reactance. (E9G10) On the Smith chart, shown in Figure E9-3, the name for the large outer circle on which the reactance arcs terminate is the reactance axis. (E9G06) Points on the reactance axis have a resistance of 0 ohms. When oriented so that the resistance axis is horizontal, positive reactances are plotted above the resistance axis and negative reactances below.

The process of normalization with regard to a Smith chart refers to reassigning impedance values with regard to the prime center. (E9G08) The prime center is the point marked 1.0 on the resistance axis. If you’re working with a 50 ohm transmission line, you’d normally divide the impedances by 50, meaning that a 50 ohm resistance would then be plotted on the resistance axis at the point marked 1.0. A reactance of 50 + j100 would be plotted on the resistance circle going through the prime center where it intersects the reactance arc marked 2.0.

Impedance along transmission lines can be calculated using a Smith chart. (E9G01) Impedance and SWR values in transmission lines are often determined using a Smith chart. (E9G03) Standing-wave ratio circles are often added to a Smith chart during the process of solving problems. (E9G09)

The wavelength scales on a Smith chart calibrated in fractions of transmission line electrical wavelength. (E9G11) These are useful when trying to determine how long transmission lines must be when used to match a load to a transmitter.

Extra Class question of the day: Direction finding

Direction finding is an activity that’s both fun and useful. One of the ways that it’s useful is to hunt down noise sources. It can also be used to hunt down stations causing harmful interference.

A variety of directional antennas are used in direction finding, including the shielded loop antenna. A receiving loop antenna consists of one or more turns of wire wound in the shape of a large open coil. (E9H09) The output voltage of a multi-turn receiving loop antenna be increased by increasing either the number of wire turns in the loop or the area of the loop structure or both. (E9H10)

An advantage of using a shielded loop antenna for direction finding is that it is electro-statically balanced against ground, giving better nulls. (E9H12) The main drawback of a wire-loop antenna for direction finding is that it has a bidirectional pattern. (E9H05)

Sometimes a sense antenna is used with a direction finding antenna. The function of a sense antenna is that it modifies the pattern of a DF antenna array to provide a null in one direction. (E9H08)

Another way to obtain a null in only one direction is to build an antenna array with a cardioid pattern. One way to do this is to build an array with two dipoles fed in quadrature. A very sharp single null is a  characteristic of a cardioid-pattern antenna is useful for direction finding. (E9H11)

Another accessory that is often used in direction finding is an attenuator. It is advisable to use an RF attenuator on a receiver being used for direction finding because it prevents receiver overload which could make it difficult to determine peaks or nulls. (E9H07)

If more than one operator can be mobilized for a direction-finding operation, they could use the triangulation method for finding a noise source or the source of a radio signal. When using the triangulation method of direction finding, antenna headings from several different receiving locations are used to locate the signal source. (E9H06)

Extra Class question of the day: Effective radiated power

Effective radiated power is a widely misunderstood concept. Effective radiated power is the term that describes station output, including the transmitter, antenna and everything in between, when considering transmitter power and system gains and losses. (E9H04)

The effective radiated power, or ERP, is always given with respect to a certain direction. Let’s think about this for a second. If your transmitter has an output of 100 W, the maximum power that the antenna can radiate is also 100 W. Transmitting antennas are, after all, passive devices. You can’t get more power out of them that you put into them. In reality, the total power output will be even less than 100 W because you will have losses in the feedline.

An antenna can, however, concentrate the power in a certain direction. The power being radiated in that direction will be more than the power radiated in that direction by a reference antenna, usually a dipole or an isotropic antenna, which is an antenna that radiates equally in all directions.

When an antenna concentrates power in a certain direction, we say that it has gain in that direction, and we specify the amount of gain in dB. If the reference antenna is an isotropic antenna, then the unit of gain is dBi. If the reference antenna is a dipole, then the unit of gain is dBd.

With that in mind, let’s take a look at an example. In this example, a repeater station has 150 watts transmitter power output, there is a 2-dB feed line loss, 2.2-dB duplexer loss, and the antenna has 7-dBd gain. To calculate the system gain (or loss), you add the gains and losses, so

Gain = 7 dBd – 2 dB – 2.2 dB = + 2.8 dB

dB Ratio
1 1.26:1
2 1.585:1
3 2:1

Now, if you recall, 3 dB is close to a gain of 2, as shown in the table at right, so in this example, to calculate the effective radiated power, you multiply the transmitter’s output power by a factor slightly less than two. This makes the effective radiated power slightly less than 15o W x 2, or 300 W. The closest answer to 300 W is 286 W. (E9H01)

Let’s look at another example. The effective radiated power relative to a dipole of a repeater station with 200 watts transmitter power output, 4-dB feed line loss, 3.2-dB duplexer loss, 0.8-dB circulator loss and 10-dBd antenna gain is 317 watts. (E9H02) In this example, the gain is equal to 10 dB – 8 dB in lossses or a net gain of 2 dB. That’s equivalent to a ratio of 1.585:1. The ERP is then 200 W x 1.585 = 317 W.

Now, lets look at an example using an isotropic antenna as the reference antenna. The effective isotropic radiated power of a repeater station with 200 watts transmitter power output, 2-dB feed line loss, 2.8-dB duplexer loss, 1.2-dB circulator loss and 7-dBi antenna gain is 252 watts. (E9H03) In this example, the gain is equal to 7 dB – 2 dB – 2.8 dB – 1.2 dB = 1 dB. That’s equivalent to a ratio of 1.26:1, so the ERP is 200 W x 1.26 = 252 W.

Extra Class question of the day: Wire and phased vertical antennas

There are many ways to put up antennas that are directional. Yagis are directional antennas, but they require a structure, such as a tower, to get them high in the air. One way to get directionality without a tower is to use phased vertical arrays.

In general, the phased vertical array consists of two or more quarter-wave vertical antennas. The radiation pattern that the array will have depends on how you feed the vertical antennas.

So, for example, the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase is a figure-8 oriented along the axis of the array. (E9C01) The radiation pattern of two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase is a cardioid. (E9C02) The radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase is a Figure-8 broadside to the axis of the array. (E9C03)

A rhombic antenna is often used for receiving on the HF bands. A basic unterminated rhombic antenna is described as bidirectional; four-sides, each side one or more wavelengths long; open at the end opposite the transmission line connection. (E9C04) The disadvantages of a terminated rhombic antenna for the HF bands is that the antenna requires a large physical area and 4 separate supports. (E9C05) Putting a terminating resistor on a rhombic antenna changes the radiation pattern from bidirectional to unidirectional. (E9C06)

Figure E9-2: Elevation Pattern

The type of antenna pattern over real ground that is shown in Figure E9-2 is an elevation pattern. (E9C07) The elevation angle of peak response in the antenna radiation pattern shown in Figure E9-2 is 7.5 degrees. (E9C08) The front-to-back ratio of the radiation pattern shown in Figure E9-2 is 28 dB. (E9C09) 4 elevation lobes appear in the forward direction of the antenna radiation pattern shown in Figure E9-2. (E9C10)

How and where you install an antenna affects its radiation pattern. For example, the far-field elevation pattern of a vertically polarized antenna is affected when it is mounted over seawater versus rocky ground. What happens is that the low-angle radiation increases. (E9C11) The main effect of placing a vertical antenna over an imperfect ground is that it reduces low-angle radiation. (E9C13) When constructing a Beverage antenna, remember that it should be one or more wavelengths long to achieve good performance at the desired frequency. (E9C12)