## Extra Class question of the day: Antenna patterns: gain as a function of pattern; antenna design (computer modeling of antennas); Yagi antennas

Many amateurs use directional antennas because they are said to have “gain.” When this term is used, what it means is that a directional antenna will output more power in a particular direction than an antenna that is not directional. This only makes sense; You can’t get more power out of an antenna than you put in. Assuming each is driven by the same amount of power, the total amount of radiation emitted by a directional gain antenna compared with the total amount of radiation emitted from an isotropic antenna is the same. (E9B07)

To evaluate the performance of directional antennas, manufacturers will measure the field strength at various points in a circle around the antenna and plot those field strengths, creating a chart called the antenna radiation pattern. Figure E9-1 is a typical antenna radiation pattern.

The antenna radiation pattern shows the relative strength of the signal generated by an antenna in its “far field.” The far-field of an antenna is the region where the shape of the antenna pattern is independent of distance. (E9B12)

From the antenna radiation pattern, we can tell a bunch of things about the antenna. One of them is beamwidth. Beamwidth is a measure of the width of the main lobe of the radiation pattern. To determine the approximate beamwidth in a given plane of a directional antenna, note the two points where the signal strength of the antenna is 3 dB less than maximum and compute the angular difference. (E9B08) In the antenna radiation pattern shown in Figure E9-1, 50 degrees is the 3-dB beamwidth. (E9B01)

Another parameter that’s important for a directional antenna is the front-to-back ratio. In a sense, this is a measure of how directional an antenna really is. The higher this ratio, the more directional the antenna. In the antenna radiation pattern shown in Figure E9-1, 18 dB is the front-to-back ratio. (E9B02)

A similar parameter is the front-to-side ratio. In the antenna radiation pattern shown in Figure E9-1, the front-to-side ratio is 14 dB. (E9B03)

When reviewing an antenna radiation pattern, you need to remember that the field strength measurements were taken at a particular frequency. When a directional antenna is operated at different frequencies within the band for which it was designed, the gain may change depending on frequency. (E9B04)

Many different design factors affect these antenna parameters. For example, if the boom of a Yagi antenna is lengthened and the elements are properly retuned, what usually occurs is that the gain increases. (E9B06) Gain isn’t everything, however. What usually occurs if a Yagi antenna is designed solely for maximum forward gain is that the front-to-back ratio decreases. (E9B05)

To help design antennas, many amateurs use antenna modeling programs. All of these choices are correct when talking about the information obtained by submitting the details of a proposed new antenna to a modeling program (E9B14):

• SWR vs. frequency charts
• Polar plots of the far-field elevation and azimuth patterns
• Antenna gain

The type of computer program technique commonly used for modeling antennas is method of moments. (E9B09) The principle behind a method of moments analysis is that a wire is modeled as a series of segments, each having a uniform value of current. (E9B10)

The more segments your simulation uses, the more accurate the results. The problem with using too many segments, though, is that the program will take a very long time to run. You don’t want to use too few segments, though. A disadvantage of decreasing the number of wire segments in an antenna model below the guideline of 10 segments per half-wavelength is that the computed feed point impedance may be incorrect. (E9B11)

The abbreviation NEC stands for Numerical Electromagnetics Code when applied to antenna modeling programs. (E9B13) This is different from the more common definition of NEC, which is the National Electrical Code.

## Extra Class question of the day: automatic message forwarding; stations aboard ships or aircraft

Some amateur radio systems automatically forward messages for other amateur radio stations. Winlink is one such system. There is always a question of who is responsible when an automatically-controlled station forwards a message that violates FCC rules.

If a station in a message forwarding system inadvertently forwards a message that is in violation of FCC rules, the control operator of the originating station is primarily accountable for the rules violation, (E1A08) This is very similar to the situation where a repeater is used to send messages that violate FCC rules.

The first action you should take if your digital message forwarding station inadvertently forwards a communication that violates FCC rules is to discontinue forwarding the communication as soon as you become aware of it. (E1A09) This is also similar to what a repeater control operator should do if a repeater user is violating FCC rules.

Operating an amateur radio station on a ship or an airplane can be a lot of fun, but there are some rules that govern this operation. For example, if an amateur station is installed aboard a ship or aircraft, its operation must be approved by the master of the ship or the pilot in command of the aircraft before the station is operated. (E1A10) Any FCC-issued amateur license or a reciprocal permit for an alien amateur licensee is required when operating an amateur station aboard a US-registered vessel in international waters. (E1A11)

Even when operating from a ship, there must be a control operator. Any person holding an FCC-issued amateur license or who is authorized for alien reciprocal operation must be in physical control of the station apparatus of an amateur station aboard any vessel or craft that is documented or registered in the United States. (E1A13)

## Mobile Apps for Ham Radio?

So, I’m at a mini-conference for mobile app developers. I currently don’t do mobile apps, but since I am a freelance Web developer, and a lot of the stuff people used to do on the Web is moving to mobile devices, I figured I better get on board.

For example, I do a website for a construction-industry trade magazine. This website is reallycrying to have a companion mobile app. One reason for this is that many of the readers are mobile types. That is to say that they are on the road a lot and not sitting in front of a computer.

The question is how the mobile app would be different from the website. Will the mobile app users want to read magazine articles? Will they want more news? Is there anything that we can give them to help them do their jobs better?

Of course, after pondering this for a while, I started thinking about ham radio mobile apps. There are already EchoLink apps out there, and I would suppose that there are already study guide/practice test apps (although possibly not). One idea that occurred to me is to develop an app that would allow users to send Morse Code to one another. This could be used for code practice as well text (code?) messaging.

What do you think? Are there any good amater-radio mobile apps out there already? What kind of amateur-radio mobile apps would you like to see?

## From the trade magazines – 7/25/12

Here are a couple of items from the electronics engineering trad magazines that hams might find interesting:

Digital and analog PC TV dongles—the basics. Some amateur radio operators are using these dongles as a software-defined radio (SDR).

Can public-safety radio’s P25 survive LTE? P25 has been with us since 1988, but its capacity and bandwidth are being obsoleted by the latest and anticipated next generations of cellular technology.

Material effectively replaces gold. Impact Coatings claims that its Silver MaxPhase performs like gold while carrying a much lower price tag.

## Frequency allocation chart cuts to the chase

On the HamRadioHelpGroup there was recently talk about frequency allocation charts. Someone pointed to the NTIA chart. This is a great chart, but several hams seemed to prefer the xkcd chart:

Click on the image to see the full-sized chart.

A while back, I wrote about carving out time for amateur radio. Well, I just ran into another article along those lines titled,”A Geek’s Guide to Budgeting Hobbies.” The difference is that this article talks about budgeting funds as well as budgeting time. The following are the bits of advice that I found the most interesting or useful:

• Budget at least 15 minutes per day for each hobby.
• Take a day or two of your vacation time every year to work on a hobby.
• Learn a new skill every year. For example, I have decided that, in 2012, I’m going to learn how to do antenna modeling.
• Don’t overspend right off the bat. The example they use is photography, noting that buying a \$5,000 DSLR camera isn’t going to make a newbie a great photographer. Same goes for amateur radio. Buying a \$5,000 K3 right after you get your Tech ticket isn’t going to automatically make you a great ham.

## More from Dayton 2012

After going through the materials I brought back from Dayton, I found a few things that I failed to mention in my previous post.

• Horse fence antennas by KF4BWG. I’ve seen this guy at the last couple of Daytons that I’ve attended, and every time I see his antennas, I think what a great idea this is. Then, I make a mental note to go to Tractor Supply or some such place and get some of this material and make my own. Then, I promptly forget to do it.
This does seem like a great idea, though. Not only would the antenna be very strong and light, but it should also be very broadband.  KF4BWG claims an SWR less than 1.4:1 across the entire 80m band, less than 1.3:1 across the entire 40m band, and 1.1:1 across the 20m, 15m, and 10m bands.
When I mentioned to KF4BWG my plans to duplicate his antenna on my own (his cost \$85), he told me that the quality of the fencing material that Tractor Supply sells is not as high as the stuff he uses. That may be true, but I’d bet it will  work just fine. Now, I just gotta do it.

• TubeProjects.Com. I think that I may have written about this company/website  before. The website lists three “products:” an audio amp, a benchtop power supply, and a VTVM. I called them products, but all the website is selling is construction manuals…at \$35 a pop.  They do mention that they plan to sell chassis for these projects in the future. Once nice feature is that they have a resources page that lists  parts sources, books, and other websites with tube project information.
• Society of Amateur Radio Astronomers (SARA). As if I didn’t have enough going on, I’m tempted to join SARA. According to the website, the Society of Amateur Radio Astronomers (SARA) is an international society of dedicated enthusiasts who teach, learn, trade technical information, and do their own observations of the radio sky. SARA was organized in 1981, and today has hundreds of members worldwide. The group consists of optical astronomers, ham radio operators, engineers, teachers and non-technical persons.
At their booth, the SARA people were touting the Radio Jove Project, a “hands-on educational activity that brings the radio sounds of the Sun, Jupiter, and the Milky Way to terrestrial students, teachers, and the general public.” They sell a \$190 starter kit that includes a 20m direct-conversion receiver, parts to construct two dipoles, and a CD ROM with SkyPipe software and general information. Since many hams will already have a 20m receiver, and know how to build a 20m dipole, it seems to me that all you’d need is the software.

## Dayton 2012: Another great ham radio experience

My Dayton experience started at 3:45 am Thursday morning. That’s when I had to get up so that I could make it to the Fairborn Holiday Inn in time for the first session of this year’s Four Days in May (FDIM). FDIM is a one-day conference put on by the QRP Amateur Radio Club International and is a great way to start the “Dayton experience.”

There were somewhere between 300 and 400 attendees at this year’s event, and we were treated to six very fine presentations. They included talks on using microcontrollers for various projects, software-defined radio, VHF and UHF for QRPers, homebrewing with “hollow state” devices (more commonly known as tubes), using open-source electronic design tools, and operating pedestrian mobile. The two talks that I enjoyed the most were “Hollow State (Thermatron) Homebrewing” by Grayson, TA2ZGE/KJ7UM and “Leveraging Free and Open Source Tools in Homebrewing” by Jason, NT7S.

Two things about TA2ZGE’s talk stood out for me.  First, was his method for homebrewing tube circuits. What he does is to take a Dremel tool and create pads on a bare piece of circuit board material, including pads that you can solder a tube socket to. Using this breadboard, you can create prototypes “Manhattan” style. Second, was the list of online resources. I’ll post those in another blog post. Grayson’s talk has certainly given me the incentive to use those “tubs of tubes” as I’ve been threatening to do now for several years.

Jason’s talk was about how he used open-source design tools to create his latest kit, the OpenBeacon, a crystal-controlled QRPp beacon transmitter. There are more out there than I realized. I’m thinking of asking Jason if he would be interested in expanding his paper into a small book that I could publish for him.

Thursday evening, they had their normal show and tell and vendor night. At this event, those selling kits and keys set up shop in the ballroom. Jason was selling his kits and the Four States QRP club had some of their kits there, too. I don’t know how much, if anything, they charge the vendors, but perhaps next year, I’ll take some of my books. They’re not exactly the right audience for them, but perhaps they’ll buy them for friends and family.

Friday morning, I got up early again, so that I could make the 7:30am bus to the Hamvention. We arrived about 8:00 am, just as the gates were opening. The first thing that I did was to head to the FAR Circuits tent, which is–as the name implies–at the far end of the flea market. There, I made my first purchases, a board to make a regenerative receiver and one to make an audio breakout box.

The rest of the day was a combination of wandering the aisles of the flea market, fighting the crowds inside the arena, attending the odd seminar, and meeting people that I know. One of the guys I ran into was Dennis, KT8K. He asked me what I thought was this year’s flea market “theme.” Every year, he says, there is always an abundance of one type of equipment or model of radio.

He’s right, too. One year, for example, I saw a dozen or more Icom IC-735s. This year, I saw none. Oddly enough, this year I saw a lot of Swan transceivers and DX-60 transmitters. There were also lots of more modern transceivers for sale, too. I even saw a K3 for sale, although by the time I got to it, it had been sold.

Another fellow that I ran into was Ed, N4EDT. I probably wouldn’t have stopped to speak to him, but he was wearing a shirt with the Rotarians on Amateur Radio (ROAR) logo on it. I introduced myself to him, and we had an interesting discussion about what kind of service project that ROAR might want to start. Since he is the Assistant Director for Education for the ARRL’s Southeastern Division, he was advocating a local project. I, on the other hand, still favor an international project that would promote amateur radio in a developing country. We also talked about possibly having a ROAR booth at Dayton next year.

By the time, 4:30 pm rolled around, I was pretty hot and tired. Temperatures topped 80 degrees, and on the blacktop surface of the flea market, temperatures were undoubtedly higher. I was happy to get on the bus and head back to the hotel.

Saturday, was pretty much the same story, except it was even hotter. The temperature almost hit 90 degrees. I didn’t bring any sunscreen, either, so I got a little rosy.

I ran into some people that I knew that had just come down for the day, or perhaps that I’d missed the day before. One guy I ran into at the Ohio Repeater Council booth, pulled out his new Elecraft KX-3 and gave me a quick demo. It’s actually quite a cool, little radio. I’m still saving up for a K-3, though.

One forum that I attended on Saturday was the Drake forum. The room was packed with people still keeping alive their old Drake equipment. The reason that I attended was I have a friend who recently was given some Drake C-Line equipment. He wants to find a good home for them. After attending this forum, I’m now thinking about buying it from him and using them in my station. I know that if I ever have any trouble, I’ll have plenty of guys out there who can help me.

After the Drake forum, I went to the food court for a slice of pizza and a glass of beer. Seating is catch as catch can, so I shared a table with several other hams. This is great because you get to meet all kinds of different people.

This year, an older gentleman sat down next to me with his beer. We got to chatting, and as it turned out, this was his 55th straight year attending the Dayton Hamvention! He started going before it was even held at Hara Arena, and even after they moved to Hara, they didn’t use the entire facility as they do now. I’m really glad that I got to speak with him.

I didn’t really go down to Dayton with much of a shopping list. My short list included more PowerPole connectors, the circuits boards I mentioned earlier, and I was going to buy a mic boom for WA2HOM. I got the connectors and circuit boards, but decided against the boom.

I did pick up a bunch of other little stuff including some strain reliefs, more clamp-on ferrite cores, a paddle pad from Vibroplex (\$1) to keep the paddle down at the museum from sliding around, and some tube sockets! One of the vendors there had a box of tube sockets that they were selling for a quarter apiece or five for a dollar. I picked out five and paid the lady, and as I was walking away, I decided that they were such a good deal that I went back and bought five more.

My biggest purchase was NT7S’s OpenBeacon QRSS transmitter. It cost me \$40. It looks like a very nice kit, and I’m hoping to be on 30m QRSS shortly with it. The nice thing about this transmitter is that it has a microcontroller that lets it transmit DFCW and Hellschreiber, in addition to CW. It should be fun to both build and operate.

I almost bought a K3. I stopped by the Elecraft booth and picked up an order sheet, but decided against it. If they had been offering more than a \$50 show discount (<2%), I might have gone for it, but that just wasn’t enough incentive.

Too rich for my blood
In other news, both Kenwood and FlexRadio both introduced new radios at Dayton. Perhaps the most buzz was around the Kenwood TS-990. Of course, they didn’t really have a working model. There’s not even any information on the Kenwood USA website.

What they did have was a mockup under a Plexiglass cover. In addition to being incredibly expensive, the radio is huge! I heard someone joke that to produce this radio, Kenwood is going to have to corner the market on buttons and knobs. If you’ve seen the photo in QST (which was allegedly produced with Photoshop), you’ll know what I mean.

The other radio with a bit of buzz is the new FlexRadio FLEX-6000. For the past couple of weeks, the FlexRadio website was proclaiming that this radio was going to be a game changer. Perhaps it is, but at \$6,000+, this radio is out of my league, and too expensive for the majority of radio amateurs. That being the case, I really don’t know what all the buzz is about.

I’m sure that the TS-990 and the FLEX-6000 are both great radios, but I think that the law of diminishing returns applies here. At some point, are you really getting \$6,000 or \$12,000 of fun out of the radio? I don’t think that I would.

Well, that’s it. Another Dayton Hamvention is in the bag. It was a lot of fun, and I’m already looking forward to next year. In addition to possibly participating with other Rotary Club members in a ROAR booth, I’m thinking about pushing for an adult education forum. I think that’s something that’s both needed and would be popular. I’ll just have to make sure to leave enough time to hit the flea market and grab some more tube sockets or coax or whatever.

## 21 Things to Do: Find an Elmer

Amateur radio can be a complicated hobby. You will, undoubtedly, have questions about the technology, questions about the rules, and questions about operating procedures. An “Elmer” is someone who can help answer those questions and help you avoid some of the pitfalls of the hobby. He or she is a ham that you can go to when you have a question about what rig to buy, when you want to borrow an antenna analyzer, or when you’re having trouble understanding a particular concept. If you haven’t already, you might want to find an Elmer.

The term Elmer first appeared in the March 1971 issue of QST magazine. In that issue, Rod Newkirk, W9BRD, called them “the unsung fathers of Amateur Radio.” He wrote that an Elmer is “the ham who took the most time and trouble to give you a push toward your license.”

Where do you find an Elmer? Well, the first place you might look is the club you just joined. Lots of the “old timers” there are more than happy to help newcomers, and many clubs have “Elmer” programs. Ask for help and ye just may receive.

Nowadays, you might find your Elmer online. There are lots of websites and mailing lists that are geared towards helping people become better amateur radio operators. One mailing list that I am a member of is the HamRadioHelpGroup mailing list (http://groups.yahoo.com/group/HamRadioHelpGroup/).

You probably can get by without an Elmer, but without one, it’s easy to become frustrated and set aside the hobby. One ham I spoke with said, “I did not have an Elmer. I got my license, and within a year, I started a 20 year hiatus. I blame that on not having an Elmer.”

You don’t want that to happen to you. Find an Elmer and take his or her advice. You’ll get a lot more out of the hobby.

## 21 Things to Do: Go to a hamfest

You can often buy stuff like power cords and connectors at bargain prices at a hamfest.

When I was a kid in Michigan, we used to call a ham radio swap meet a “swap and shop.” Nowadays, they’re mostly known by the term “hamfest.” Whatever name you know them by, they’re both educational and a lot of fun.

There are a lot of reasons to go to a hamfest, including:

• You get to see a lot of ham radio gear in one place.
• You might be able to get a good deal on some used (or new) equipment.
• You might find something that will be fun to play with.
• You get to meet hams face-to-face that you’ve only talked to on the air.

You never know what you’ll find at a hamfest. If it’s a decent-sized hamfest, chances are you’ll find equipment ranging from radios made in the 1950s with vacuum tubes to modern computer-controlled transceivers. If nothing else, you’ll get an education on the wide range of amateur radio equipment that’s out there.

Can you get a good deal on a radio? Possibly, although these days so much stuff is sold on EBay and via the online ham classifieds on QRZ.Com, eHam.Net, and other sites, that getting a real “steal” is getting harder and harder. One thing is for sure, if you’re a new ham and don’t really know how to evaluate a particular piece of equipment, get your Elmer to look over a purchase before you hand over your money. What may look like a bargain, may end up costing more than a new radio.

What you can often get a good deal on are small parts, such as connectors, power cords, speakers, etc. You never know when you’ll need a 1/4-in. phone plug to put on the end of a set of headphones. A friend of mine jokes that at every hamfest he always buys a handful of different connectors. Hamfests are good places to stock up on these types of things.

You’ll find more than used equipment at a hamfest, though. Many dealers will bring new equipment to a hamfest, especially if it’s one of the big hamfests. This is your chance to look at a number of different radios that you may have only been able to look at in catalogs and compare different models. In addition, dealers often offer “hamfest prices,” so you may be able to get that radio at a slight discount.

Hamfests are also good places to connect with other hams. Quite often, you’ll meet guys that you’ve only talked to on the air. It’s a lot of fun to connect a name and callsign with a face. Sometimes, different ham groups, such as ARES/RACES groups or QRP clubs, will set up a table to promote their group. You can use this opportunity to find out more about these groups and their activities.

To find a hamfest near you, go to the ARRL Hamfests and Conventions Calendar page.