HamRadioNow.tv

Ham Radio NowI don’t know how I missed watching HamRadioNow, but now that I’ve seen my first episode, you can bet that I’m going to be a regular viewer from now on. If you ask me, it’s more interesting than HamNation on TWIT.

The last episode I watched is episode #24, which talks about WB2JKJ, the radio club of Junior High School #22 in New York City. You’ve seen the ads in QST and the other ham radio magazines. If you ever wondered about those ads–and the program behind it–you should watch this episode.

The program is actually not about getting kids their amateur radio licenses. Instead, it’s about using amateur radio to teach language arts, geography, etc. And, the program is now more than just a New York City kind of thing. The program reaches out to all educators nationwide.

This episode of HRN was a real eye-opener for me. If you’re at all interested in ham radio in education, watch this episode. If you’re at all interested in any other aspect of ham radio, watch one of the other 20+ episodes.

Contest to award HF gear to youth in January

This is both a great PR move by Amateur Radio Supplies, a company I’ve never heard of, and a good thing for amateur radio. I also love that they’re including a set of paddles :) …..Dan

Sep 26, 2012 -
Amateur Radio Supplies of Haverhill, Mass., announced today a new biannual giveaway to promote youth in amateur radio DXing and contesting.

“Getting on HF (high frequency) in today’s economy is very challenging for many, but especially for our youth operators,” said Jeff Demers, owner, Amateur Radio Supplies. “Many youth operators are unable to purchase the needed equipment to get on the air.  Here at Amateur Radio Supplies, we want them to experience the joy that has propelled us in this hobby for many decades. Thus, on January 1, 2013, we’ll be doing the first of many station sponsorships to support youth in DXing and contesting.”

Amateur Radio Supplies will give a complete HF (high frequency) station to the selected applicant, including:

  • Alinco DX-SR8T/E 160-6m All Mode Transceiver & 30 Amp PS
  • LDG AT-100 Pro II Desktop Antenna Tuner
  • Choice of Rugged All Band G5RV or HyGain DX-77A Vertical
  • 100’ of Premium RG-213 Coax
  • Vibroplex Brass Racer Iambic Paddles
  • SignaLink USB Sound Card for Digital Modes
  • Heil Pro Set Plus Headset

Applicants from any country under the age of 21 are invited to provide brief answers to the following three questions, as well as their name, call sign, and license class, online at http://www.amateurradiosupplies.com/youth-s/222.htm.

1. How often are you able to operate on the HF bands?
2. Where (what QTH) do you typically operate from?
3. How do you intend to use the equipment provided?

Nominations will also be accepted.  If you know of a deserving youth, please email Randy Rowe at randy@amateurradiosupplies.com.

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.

From the trade magazines – 092612

Three more articles from recent editions of the electronics trade magazines.

HeathkitHeathkit: A right-time, right-place business. Heathkit was a popular electronics company for decades before its demise earlier this year. Former employees Lou Frenzel and Chas Gilmore share some memories and discuss the factors that led to its closing. Lou Frenzel is W5LEF.

In the article, he notes how he was instrumental in developing the Heath/Zenith line of computer kits. At that time, I was a fledgling test engineer working for Memorex (remember them?) making the 8-in. floppy drives that were an option for those computers.

Real-world testing of wi-fi hotspots. This article talks about both the RF testing and data communications testing needed to ensure a good wi-fi hotspot.

How to simulate cable in SPICE. This article covers the two main loss effects related to cables (the skin effect and dielectric losses) and presents a simple cable modeling method for use in standard SPICE simulators.

Extra Class question of the day: Amplifiers

There are several classifications of amplifiers, based on their mode of operation. In a class A amplifier is always conducting current. That means that the bias of a Class A common emitter amplifier would normally be set approximately half-way between saturation and cutoff on the load line. (E7B04)

In a class B amplifer, there are normally two transistors operating in a “push-pull” configuration. One transistor turns on during the positive half of a cycle, while the other turns on during the negative half. Push-pull amplifiers reduce or eliminate even-order harmonics. (E7B06)

A Class AB amplifier operates over more than 180 degrees but less than 360 degrees of a signal cycle. (E7B01) Class B and Class AB amplifiers are more efficient than Class A amplifiers.

A Class D amplifier is a type of amplifier that uses switching technology to achieve high efficiency. (E7B02) The output of a class D amplifier circuit includes a low-pass filter to remove switching signal components. (E7B03)

Amplifiers are used in many different applications, but one application that is especially important, at least as far as signal quality goes, is RF power amplification. RF power amplifiers may emit harmonics or spurious signals, that may cause harmful interference.

One thing that can be done to prevent unwanted oscillations in an RF power amplifier is to install parasitic suppressors and/or neutralize the stage. (E7B05) An RF power amplifier be neutralized by feeding a 180-degree out-of-phase portion of the output back to the input. (E7B08) Another thing one can do to reduce unwanted emissions is to use a push-pull amplifier. Signal distortion and excessive bandwidth is a likely result when a Class C amplifier is used to amplify a single-sideband phone signal. (E7B07)

While most modern transceivers use transistors in their final amplifiers, and the output impedance is 50 ohms over a wide frequency range. A field effect transistor is generally best suited for UHF or microwave power amplifier applications. (E7B21)

Many high-power amplifiers, however, still use vacuum tubes. These amplifiers require that the operator tune the output circuit. The tuning capacitor is adjusted for minimum plate current, while the loading capacitor is adjusted for maximum permissible plate current is how the loading and tuning capacitors are to be adjusted when tuning a vacuum tube RF power amplifier that employs a pi-network output circuit. (E7B09)

Figure E7-1

The type of circuit shown in Figure E7-1 is a common emitter amplifier. (E7B12) In Figure E7-1, the purpose of R1 and R2 is to provide fixed bias. (E7B10) In Figure E7-1, what is the purpose of R3  is to provide self bias. (E7B11)

Figure E7-2

In Figure E7-2, the purpose of R is to provide emitter load. (E7B13) In Figure E7-2, the purpose of C2 is to provide output coupling. (E7B14)

Thermal runaway is one problem that can occur if a transistor amplifier is not designed correctly. What happens is that when the ambient temperature increases, the leakage current of the transistor increases, causing an increase in the collector-to-emitter current. This increases the power dissipation, further increasing the junction temperature, which increases yet again the leakage current. One way to prevent thermal runaway in a bipolar transistor amplifier is to use a resistor in series with the emitter. (E7B15)

RF power amplifers often generate unwanted signals via a process called intermodulation. Strong signals external to the transmitter combine with the signal being generated, causing sometimes unexpected and unwanted emissions. The effect of intermodulation products in a linear power amplifier is the transmission of spurious signals. E7B16() Third-order intermodulation distortion products are of particular concern in linear power amplifiers because they are relatively close in frequency to the desired signal. (E7B17)

Finally, there are several questions on special-application amplifiers. A klystron is a VHF, UHF, or microwave vacuum tube that uses velocity modulation. (E7B19) A parametric amplifier is a low-noise VHF or UHF amplifier relying on varying reactance for amplification. (E7B20)

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)

ARRL Executive Committee to Meet Saturday, September 29

The ARRL Executive Committee is meeting today, Saturday, September 29, in Denver, CO.  Here are a few agenda items that I found interesting:

  • 4.1.1. Consideration of strategies to improve the FCC Amateur Radio enforcement program.
  • 4.1.4. Consideration of draft Petition for Rule Making for domestic implementation of allocations at 472-479 kHz and 135.7-137.8 kHz.

ARRL President Kay Craigie, N3KN is the Executive Committee chair. Five Division Directors who are elected by the ARRL Board of Directors are also on the committee:

  • Midwest Division Director Cliff Ahrens, K0CA;
  • Northwestern Division Director Jim Fenstermaker, K9JF;
  • Central Division Director Dick Isely, W9GIG;
  • Rocky Mountain Division Director Brian Mileshosky, N5ZGT, and
  • West Gulf Division Director David Woolweaver, K5RAV. ARRL

Chief Executive Officer David Sumner, K1ZZ, and ARRL First Vice President Rick Roderick, K5UR, are non-voting members of the Executive Committee. ARRL General Counsel Chris Imlay, W3KD, and Second Vice President Bruce Frahm, K0BJ, will also attend the meeting.

Click here to download the entire agenda, and feel free to contact any and all of the Executive Committee members if you have comments, questions, or concerns.

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: Frequency counters and markers

To measure the frequency of a signal, you use an instrument called a frequency counter. The purpose of a frequency counter is to provide a digital representation of the frequency of a signal.(E7F09) A frequency counter counts the number of input pulses occurring within a specific period of time. (E7F08)

To accurately measure high-frequency signals digitally, you need a highly stable and accurate frequency source, called the time base. The time base provides an accurate and repeatable time period, over which you count the number of pulses of the test signal. The accuracy of the time base determines the accuracy of a frequency counter. (E7F07)

An alternate method of determining frequency, other than by directly counting input pulses, that is used by some counters is period measurement plus mathematical computation. (E7F10) An advantage of a period-measuring frequency counter over a direct-count type is that it provides improved resolution of low-frequency signals within a comparable time period. (E7F11)

You also need an accurate and stable time base to generate and receive microwave signals. All of these choices are correct when talking about techniques for providing high stability oscillators needed for microwave transmission and reception: (E7F05)

  • Use a GPS signal reference
  • Use a rubidium stabilized reference oscillator
  • Use a temperature-controlled high Q dielectric resonator

If you want to measure a signal whose frequency is higher than the maximum frequency of your counter, you might use a prescaler. The purpose of a prescaler circuit is to divide a higher frequency signal so a low-frequency counter can display the input frequency. (E7F01) A prescaler would, for example, be used to reduce a signal’s frequency by a factor of ten. (E7F02)

You might use a decade counter digital IC in a prescaler circuit. The function of a decade counter digital IC is to produce one output pulse for every ten input pulses. (E7F03)

In some cases, you might use a flip-flop. Two flip-flops must be added to a 100-kHz crystal-controlled marker generator so as to provide markers at 50 and 25 kHz. (E7F04) The purpose of a marker generator is to provide a means of calibrating a receiver’s frequency settings. (E7F06) You mostly find marker generators in older, analog receivers.

On the Internet – cat sends Morse Code, IARU band plans, Tek gets with the program

Sorry about not posting much here lately beside the Extra Class questions of the day, but I’ve been pretty busy with my work and I really do Here are some more links to ham-related items on the Internet:

Cat sends Morse Code. I love cats, and while there are many videos of cute cats on the Internet, here’s one that shows a cat sending Morse Code. (Well, not really, but if you watch, you’ll see what I mean.) As I was watching this video, and then viewing a couple of other cute cat videos on this site, I noticed that my cat, Poochie, who was sitting on my lap, was intently watching the videos as well. That’s the first time that I’ve ever noticed that he was interested in what was going on on my computer screen.

IARU Region 2 band plans. A year from now, the IARU Region 2 General Assembly will take place.  On the agenda are new  Region 2 band plans.  These band plans set the framework on how we use our bands and what modes we use in specific frequencies. If you’re interested in this topic, this Web page contains information on the current band plan and the procedure that will be followed for updating them next year.

Tek hypes ham radio.Tektronix, the big test instrument manufacturer, has many hams working for them. Perhaps the most well-known is Alan, W2AEW. I’ve blogged about him before. He has produced a really great series of videos on YouTube. He’s now blogging on the Tektronix website, and his latest post is an introduction to amateur radio.