• 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

Having said that, you should submit a log, even if you only make a handful of contacts. At WA2HOM, we participated in the CQWW SSB contest last fall. We only operated for a short time, as we can only operate when the museum is open. Even so, we recently received a certificate for being the highest scorer in the single transmitter, multi-operator category in the 8th call district. As it turns out, we were the only entry in this category, but so what? We’re champions!

Now, let’s look at the wrong answers:

• Interference to other amateurs is unavoidable and therefore acceptable. It’s bad practice–as well as illegal–to cause harmful interference whenever you’re operating, even during contests.
• It is mandatory to transmit the call sign of the station being worked as part of every transmission to that station. Part 97 requires only that you identify your station, at least once every ten minutes during a contact and at the end of a contact. Even during normal operation, you don’t have to give the callsign of the station being worked.
• Every contest requires a signal report in the exchange. Many contests no longer require a signal report in the exchange.The reason for this is that the signal reports exchanged are rarely true signal reports. That being the case, why bother to exchange them?

In conjunction with that, I’m also planning to do an “Extra Class Question of the Day” here on my blog. In reality, the “question of the day” will cover more than one question, as so many of them are related. As in my study guides, the correct answer will be highlighted, and the question will be marked with the pool question number.

Today’s question of the day is about resonance. Resonance is one of the coolest things in electronics. Resonant circuits are actually what makes radio, as we know it, possible.

What is resonance? Well, a circuit is said to be resonant when the inductive reactance and capacitive reactance are equal to one another. That is to say, when

2πfL = 1/2πfC

where L is the inductance in henries and C is the capacitance in farads.

For a given L and a given C, this happens at only one frequency:

f = 1/2π√(LC)

This frequency is called the resonant frequency. Resonance in an electrical circuit is the frequency at which the capacitive reactance equals the inductive reactance.(E5A02)

Let’s calculate a few resonant frequencies, using questions from the Extra question pool as examples:

The resonant frequency of a series RLC circuit if R is 22 ohms, L is 50 microhenrys and C is 40 picofarads is 3.56 MHz. (E5A14)

f = 1/2π√(LC) = 1/6.28x√(50×10^-6 x 40×10^-12) = 1/2.8×10^-7 = 3.56 MHz

Notice that it really doesn’t matter what the value of the resistance is. The resonant frequency would be the same is R = 220 ? or 2.2 M?.

The resonant frequency of a series RLC circuit if R is 56 ohms, L is 40 microhenrys and C is 200 picofarads is 1.78 MHz. (E5A15)

f = 1/2π√(LC) = 1/6.28x√(40×10^-6 x 200×10^-12) = 1/5.6×10^-7 = 1.78 MHz

The resonant frequency of a parallel RLC circuit if R is 33 ohms, L is 50 microhenrys and C is 10 picofarads is 7.12 MHz. (E5A16)

f = 1/2π√(LC) = 1/6.28x√(50×10^-6 x 10×10^-12) = 1/1.4×10^-7 = 7.12 MHz

The resonant frequency of a parallel RLC circuit if R is 47 ohms, L is 25 microhenrys and C is 10 picofarads is 10.1 MHz. (E5A17)

f = 1/2π√(LC) = 1/6.28x√(25×10^-6 x 10×10^-12) = 1/9.9×10^-7 = 10.1 MHz

Those who say it’s not point out that years ago we had magazines, such as Popular Electronics and Electronics Illustrated, companies like Heathkit. They also point out that it was possible to disassemble TVs and radios for the parts and use them for your own projects.

Schweber, however, thinks that it is easier today for hackers and experimenters. He writes that  those magazines may be out of business, but we now have access to “countless user groups, informal forums, and blogs” on the Internet.

One thing he failed to mention was the hacker/maker groups that have sprouted up around the country. Here in Ann Arbor, for example, we have a group called Go Tech that provides support for hackers and makers of all stripes. You’ll find groups like this all around the U.S.

I tend to agree with Schweber that while the environment has certainly changed for experimenters, it is definitely better. What do you think?

ONE TOPIC MANY members will appreciate is a free, digital version of QST via the Internet.  This version offers the ability to read our membership journal online in a manner quite similar to that in which we read the hard-copy version.  It also offers the ability to include full schematics and other information that sometimes can merely be referenced in the print edition, as well as direct links to items contained in the ads.

Becoming accustomed to the online version may require a little familiarization, but I believe it will become a welcome enhancement to membership.

It is inevitable that two questions regarding digi-QST will arise.  The first is if a member can opt-out of receiving the hard-copy version.  The answer:  yes.  The second question is:  Is there a reduction in dues for members who opt-out of the print version.  The answer to this is no.  The hard-copy version is financed largely by advertisement, not by membership dues.

Digi-QST should be unveiled yet this winter or early spring.

I think this is great, but it sounds to me like we’ll have to read the magazine on-line rather than being able to download a PDF file.  I’ve never really liked these online magazines. Reading them is a real pain, and you often can’t download and archive them. Let’s hope the ARRL thinks about this when they set this up.

New fuse makes Heathkit happy
A couple of weeks ago, a ham friend expressed an interest in one of the Heathkit IP-2717 HV Power Supplies that I rescued from the University of Michigan’s Property Disposition center a couple of years ago. I purchased three of them at the time, one working, two not working. I told him that I’d let him have one of the non-working units for $25, exactly what I paid for them.

He agreed to the price, and we agreed to meet for lunch about a week later and make the transaction. A couple of days beforehand, though, I decided to pull one off the shelf and just have a look inside.

Well, as soon as I popped the top off, the problem was obvious. It had a blown fuse. I just happened to have that value and when I stuck a new one in, the power supply fired right up and worked like a charm. My friend not only gave me a few more bucks for fixing it, but also bought lunch!

A two-minute fix for 2m rig
This evening, as I was working a guy in ME on 30m CW, I spotted on my shelf, an old 2m FM rig that someone had given to me. It had quit working on him, and since he wanted to get something newer, he didn’t feel like fooling around with it. He told me that if I could fix it, that I could sell it or give it to someone who attended one  of my classes and was looking for a starter radio.

That radio has sat on the shelf for at least two years. When I caught sight of it this evening, though, I was inspired to open it up and see if there was anything obviously wrong with it that I could fix easily.

Sure enough, all I had to do was remove the two screws holding the top of the case to the radio and peer inside. The problem was readily apparent. Somehow, one of the connectors connecting a cable to the main board had worked itself loose. I plugged it back in, hooked it up to my power supply and 2m antenna, and worked N1RIT on the club repeater.

The point of these stories is that even though a piece of equipment might be quite complicated, often what goes wrong is something simple to fix. In the case of the power supply, all I had to do was change a fuse. All the 2m rig needed was for me to reconnect a disconnected cable.

So, next time one of your radios goes on the fritz, don’t just send it off to a repair center. Crack open the case and have a look inside. It may be a simple fix, and if it is, you’ll not only save yourself a lot of money, you’ll have the satisfaction of having fixed it yourself.

• FCC denies Anchorage VEC’s waiver request. In July 2011, the Anchorage VEC asked the FCC to permit individuals who have previously held an Amateur Radio license grant issued by the Commission — but which has expired and is beyond the two year grace period for renewal — to receive credit for elements previously passed, and thus a new license grant, without additional examination.
  I’m not altogether sure why this VEC would request this waiver. In fact, I’ve suggested that maybe it would be a good idea to regularly re-test ham radio operators.
• Minutes of ARRL Board’s winter meeting posted. The ARRL board held their annual winter meeting the weekend of January 13-14, 2012. The  minutes from that meeting have now been posted. These are always interesting and worth perusing.
  One item of interest is that the board has approved electronic voting for division elections. I wonder how that would have affected, if at all, the two elections that I participated in.
• LOTW to support CQ awards. The ARRL and CQ magazine have agreed that QSLs recorded in Logbook of the World can now be used to apply for CQ-sponsored operating awards. These are the first non-ARRL awards to be supported by LoTW. The first CQ award that you will be able to apply for via LOTW is the WPX award.

The venerable Simpson Model 60 VOM has been in production for more than 60 years.

In the Test&Measurement World group on LinkedIn, editor Martin Rowe asks, “What’s your favorite test instrument”? He gets some interesting answers, but the two top vote-getters are the Bird Model 43 Wattmeter and the Simpson Electric Model 60 VOM (see right).

About the Bird wattmeter, one engineer said, “That’s easy – The Bird Model 43 Wattmeter. No other instrument has been in production, in its original design, for so long. Since 1952, which makes next year 2012 its 60th anniversary. Also, it must be the simplest, most rugged instrument ever produced. We regularly see Model 43 Wattmeters returned to us for calibration that are 30-40 years old, still working and, when they leave our facility, as accurate as the day they first came of the production line in Solon, Ohio.”

About the Simpson VOM, another replied, “My favorite test instrument of all time is the Simpson 260. I used it back in the 1970s while serving in the US Navy. It is rugged, easy to use, and does the job!”

Those are really two classics, and either is a great choice. But, what do  you think? What’s your favorite test instrument?

Me making a point (apparently about SWR) at Saturday's One-Day Tech Class

Last weekend was pretty busy for me, ham radio-wise. It started bright and early Saturday morning with the latest One-Day Tech Class. There were twelve students in the class, and all twelve passed!

This class was a bit odd in that most of them signed up during the week before the class. So few had signed up by Saturday, January 7th, that I was even thinking that I might cancel the class.

On Sunday, January 8, I sent out a reminder to my mailing list, and after that, the class quickly filled up. Many of them were engineering students from the University of Michigan, who are part of a project that sends up weather balloons. They use amateur radio to track the balloons and to find the payloads once they’ve returned to Earth.

Hamfest not so festive
Sunday morning, I was up even earlier to attend the Hazel Park ARC hamfest. Since I was selling some junk, errrrr good stuff, I wanted to get there by 8 am. So, I was up and out of the house by 6:45 am. I needn’t have rushed, though.

Attendance was way down, and while I did sell a little over $100 worth of books and other stuff, I was hoping that I’d sell more. In particular, I thought I’d sell a few of my new “Hams Obey Ohm’s Law” stickers. I didn’t sell a single one, however. One friend of mine offered to purchase one, but I just gave him one.

I think clubs have to think twice about when they schedule these things. Holding them so early on Sunday mornings almost guarantee that only the old farts will show up for these things. And the old farts are a dwindling audience.

No propagation, no glory
Sunday night, I tried to participate in the monthly Run for the Bacon (RTFB). This low-pressure QRP contest, run by the Flying Pigs is usually a fun event. Sunday night, however, the band had gone way long by 9 pm EST, when the contest started. I managed one contact with a station in Idaho, but no one else could hear me.

To be honest, I don’t really know how much power I was running. Instead of hooking up the KX-1, I just cranked down the power on the IC-746PRO until the power out meter was showing just a single bar. I really gotta get that wattmeter kit finished.

Amateur Radio Video News (ARVN) has released high-definition videos of all the talks presented at the 2011 ARRL/TAPR Digital Communications Conference (DCC), held September 16-18. The programs are now available online on the ARVN website.

The DCC is a three-day conference on Amateur Radio digital technology. Among the video presentations are 18 seminars, the Saturday Banquet and the welcome introduction by TAPR Chairman Steve Bible, N7HPR. According to ARVN Producer Gary Pearce, KN4AQ, most of the talks are fairly technical, although there are four separate sessions that cover “Intro to” topics. “All of the talks — except the ‘Intro to’ talks — were shot in three-camera high-definition, with wireless mics for ‘close-up’ audio of the presenter, as well as the question-and-answer period,” he explained. “The ‘Intro to’ talks were shot with a single, standard-definition camera.

This year, Pearce decided to release the programs on the web instead of the DVDs that have been produced in previous years (although the DVDs will be available later). “I wanted to make the programs available more quickly and easily to a worldwide audience,” he said. “The web has become an easy, high-quality distribution medium.”