Our Tech Night meetings feature technical discussions and presentations on a broad range of topics. Our Tech Nights take place in a lab-oriented environment where hands-on elements and roundtable style discussion is encouraged. For information on the topic for our next session, see our Tech Night page.
Tech Night First Church Parking and Meeting Entrance
Parking Information: Please park in the Front Door Agency or Eaton and Berube Insurance parking lots. As you head north on Concord St., the Front Door Agency driveway is the first driveway after the church driveway. The Eaton and Berube Insurance driveway is the second driveway after the church driveway. Those that require handicap parking should use the spaces marked as such at the church parking lot. We must reserve parking directly next to the church for other church activities.
So you’ve gotten your Technician License or your General upgrade – how do you get a station on the air? This was the topic of our recent Tech Night. The following are some thoughts to get you started. If you are a new Technician, the first thing to ask is – “What do I really want to do on the air and where will I be doing it?” Here are some common answers to this question:
I spend a lot of time commuting in my car or truck and I’d like to pass the time talking with other HAMs
I will mostly be operating from my home and I want to rag chew (chat with other HAMs) and check-in to emergency, ARES and/or other nets
My plans are mostly be doing parade and other HAM activities in the field and I need something that is portable
Approaches for Tech Operators
In all of these scenarios, you will be using a combination of FM Simplex and Repeater operation on the 2 m and 70 cm bands.
If the first case is you, then you’ll want to install an FM mobile rig and antenna in your car or truck. You’ll also probably want to permanently mount a simple 2 m/70 cm antenna on your vehicle.
If the second case is your prime operating scenario, then your choices in radios probably are along two main paths. A 2 m/70 cm radio or a dual purpose HF and 2 m/70 cm capable “all in one” radio. You might take the second approach if you already have or are planning to get your General Class or Extra Class license. A 2 m/70 cm ground plane style vertical antenna that you can mount outside or perhaps in your attic would be a good choice. You might also want to consider a radio that does D-STAR or another Digital Voice mode. There are some large worldwide nets that use digital plus internet linking to reach a large population of HAMs.
If the third case is you main operating mode, then you probably want a quality HT with a good antenna. The rubber duck antenna that comes with most HTs will provide relatively weak performance. A quality 5/8 wavelength antenna and a spare battery for your HT will be a good way to go.
Approaches for General Operators
If you’ve received your General Class license and want to do HF, your biggest decision will your antenna antenna. This topic is pretty broad and we’ll cover it in more detail at our Tech Night. I usually recommend a simple wire antenna to get started. A 20m dipole mounted either horizontally or vertically is often a good first choice. It’s inexpensive and can be put up at most QTHs in a day or less.
Radio choice is also a broad topic which we will cover at our Tech Night. I would recommend a starter HF radio or a good used one (with help from an experienced HAM to select and check out). Your radio should be a 100W unit and cover all of the HF bands from 80 m – 10 m at a minimum. QRP radios (5 – 10W) are usually not a good choice for a first station. Making contacts at this power level with simple antennas can be challenging. It’s also good to have a radio which can do 6 m if that works out for you.
I highly recommend that you include digital mode capability in your first HF station. Digital modes such as PSK and RTTY provide a great way to learn to make contacts on the HF bands. Also, these modes work very well for making DX contacts with 100W and simple wire antennas.
I hope that this will get you started thinking about how to set your first station. Please come to our next Tech Night session to learn more. You can ask questions and get the benefit of experienced folks in our club. We can help you with these choices. We can also help with installing radios, antennas and getting on the air.
The most important piece of equipment in ham radio is our antenna. We are connected to the world with the magic of radio waves! Each License Exam from Technician through Extra class has questions to test our knowledge on antenna design and building skills. Home-brewed antennas are easy and relatively inexpensive projects.
This article describes a 2m, 3-element Yagi antenna construction concept that the N1FD FCC license teaching team has used over the last year for class demonstrations. The “Lego” style construction (v. 2.0) shown in the above picture is our new design that demonstrates the operating principles of the ubiquitous basic dipole antenna as well as a 2-meter, 3 element Yagi. (Note, This project evolved from an earlier effort by Diana Eng at Makezine.com, which can be seen here.
In this Newsletter issue, we will describe the construction of the “Lego” stylized antenna and show how it can illustrate basic properties of a dipole antenna. We will build a Yagi antenna with the addition of reflector and director arms in a future Newsletter article.
CONSTRUCTION of the LEGO STYLIZED ANTENNA.
The antenna demonstration unit consists of two assemblies.
A handheld receiver dipole set to a fixed frequency (e.g., 146.550 MHz). It is shown at the top of the photo above. It follows a “plumber’s delight” construction using pieces of PVC pipe for a short boom and handles. The dipole arms are two telescoping (7-28 inch) FM radio replacement antennas, available on eBay or Radio Shack ($4-6 dollars). The arms feed through the boom and are epoxied. Bridging across the arms is a common 6-volt flashlight bulb. The bulb lights up when the dipole receives a resonant rf signal.
The “Lego stylized” Yagi antenna components are shown below the receiver unit. The boom (middle item) is made of red oak dimensioned at ¾ x 1 ½ x 48 The top surface is grooved to hold an epoxied 3/16 steel rod. The bottom surface has drilled recesses to fit ¾ in PVC pipe for leg stands. The edge of the boom has two 24-inch adhesive tape rulers running from center to front and back of the boom. The rulers read-out the spacing between the driven dipole element and the parasitic reflector and director arms. In the photo, the D.E. and parasitic elements are seen below the 48 in. boom. The center element is the driven dipole and it is flanked by identical units that can be configured as either reflectors or directors. Each unit consists of two telescoping FM radio antenna rods epoxied in a grooved piece of red oak ( ¾ x 1 ½ x 3 inches) serving as “riders” on the boom. The telescope arms can be adjusted to “resonance” at any frequency in the 2-meter band. The bottom of all riders has 2 x ½ inch rare earth magnets. These allow the three antenna elements to be fixed at any position on the 48 in. boom.
You can view a closer look at the assembled Yagi antenna configuration in this video (Click on Link)
DEMONSTRATIONS OF BASIC DIPOLE BEHAVIOR.
1. Antenna Resonance Determined by Dipole Length.
As we all know, the resonance length of a dipole is given by the equation: L (in inches) = 5616/ [ Frequency (in MHz)]. We can show this fact with aid of the “receiver” antenna, which is set for a frequency of 146.55 MHz The light bulb of this antenna will light when it senses a signal of this value from our “Lego” antenna.
In the video below (Click on Link), we begin with a resonant D.E. length of 38.5 inches and see the receiver antenna light up. Next, we manually shorten the D.E. and see the bulb light dramatically dim. When the D.E. length is returned near the start value, the light bulb again brightens up.
Effect of SWR on Signal Strength.
Most modern transceivers have a built-in auto-tuner that can match SWR up to 3:1. We know this only makes the “radio happy”, still we key down without much thought on how our Tx signal degrades with a 3:1 match. The pictures below use the transmitting “Lego” dipole and receiver dipole to show the received signals for an SWR of 1.1 and 3.0. The SWR was changed by lengthening the D.E. elements by 2 inches while holding the Tx frequency at 146.55 MHz
3. Polarization Effects between Tx and Rx Antennas.
A horizontal dipole shows “horizontal” polarization; meaning the electric field vector of the rf signal is parallel to the earth surface. Similarly, a vertical dipole displays “vertical” polarization with the electric field perpendicular to the earth. We all learn this in a Technician class course.
When we use our 2m HT’s for short distance contacts, Tx and Rx antennas with opposite orientation create a huge signal loss. The effect is shown dramatically in the video below.
Our classroom constructible antenna for demonstrations in our Ham Radio license classes has evolved in design over the past year. We believe it has been a useful resource, helping students translate textbook theory to “Hands On” practice. Perhaps, this review has kindled interest for our readers to think of their Next Antenna Project!
This article discusses some work on designing a matching network to make antennas match well (low VSWR) across the entire ham band. This will be a described in more detail at the September Tech Night.
Antennas have an impedance (or match) that varies with frequency. Transmitters want to see a matched antenna with an impedance of 50 ohms. The antenna has the best match at one frequency and the match gets worse as the operating frequency changes.
Some bands and antennas are more challenging to match than others. Shortened or loaded antennas have a narrow range of match frequencies. The 75/80 meter band has a wide bandwidth in term of percentage.
Here’s a plot of the SWR for my 40 Meter Dipole. It’s a good match at 7.000 MHz and degrades to about 2:1 at 7.100 MHz. Obviously, this is not optimized.
Modern radios have built in automatically adaptive matching networks make the radios work over a wider bandwidth, but networks are lossy and reduce transmitted power.
A manual antenna tuner has a lot lower loss than the built in tuner, but it requires manual adjustment. In fact, the extra tuned circuits generally act to make the antenna have even less bandwidth.
The QUCS RF circuit simulation program has the ability to model SWR, bandwidth, matching networks based on data about antenna performance. The antenna data can come from either an antenna modeling program such as 4NEC2 or EZNEC. Or the data can come from a measurement made by a good antenna analyzer.
QUCS also has a built in optimizer. It has the ability to try hundreds of circuit values and home in on an optimal design.
The optimizer setup needs a definition of “optimal”. For the case of a broadband antenna, “The worst case SWR anywhere in the ham band shall be as low as possible”. In the terms that QUCS understands, “minimize the maximum SWR over the frequency range 7.00 to 7.35 MHz.
Here is the result from running the optimizer on the data for my mistuned 40M dipole. QUCS has designed a broadband matching network that can achieve less than 1.5:1 SWR over the whole band.
QUCS achieved this by varying the components of a filter network. I drew a general filter network and let QUCS tune the component values. This network is designed with coaxial stubs.
The model of the antenna is stored as a file in the X1 file component. Line7 is a 30-meter coax feedline. The actual matching network consists of Line 1, 2, 3, 4. Each line is 50 Ohm coax. Line 1 and 3 are configured as open stubs. The line lengths predicted by the model are…
Line 1: 7.75 meters
LIne 2: 4.47 meters
Line 3: 8.49 meters
Line 5: 8.03 meters
Here’s another example. 160-meter antennas are often implemented as shortened loaded verticals. The loading makes the match very narrow-band. The red curve in the plot below shows a top loaded 160 meter vertical. It only covers a fraction of the band.
The blue curve shows the result of an optimization run that selected the values for a 7 component matching network. It achieves about 1.7:1 across the whole band. This network uses capacitors and inductors because coax stubs would be very long on 160 meters.
The component values for this network…
C1: 3450 pF
L1: 3.954 uH
C2: 3978 pF
L2: 6.951 uH
C3: 6156 pF
L3: 2.831 uH
C4: 4778 pF
I have not built any of these networks to see how they work in practice. The 160-meter network has some extreme values and it is probably very touchy to get right. Building that network to handle Tx power will require vacuum variable capacitors in parallel with high quality stable fixed value capacitors. But, the 160 network doesn’t really need 7 components. Put in one less stage of L-C and the ripple across the passband goes up a bit.
QUCS is a great RF circuit simulator. This shows that it can work with data from an antenna model or analyzer and can optimize matching networks to create a broadband antenna.