Differences

This shows you the differences between two versions of the page.

--- user:kurser:ham_vt2023_l7 [2023/04/24 19:07] – Added some exam questions. user
+++ user:kurser:ham_vt2023_l7 [2026/03/02 17:18] (current) – loka
@@ Line 1: / Line 1: @@
 =====ETA313-07: Theory Lesson 3: Antennas, Transmission lines, Propagation =====
-[[user:kurser:ham_vt2023|Back to course information]]
+[[user:kurser:ham_vt2025|Back to course information]]
 **Recommended reading: KonCEPT page 191-229 (chapter 7 + 8) **
@@ Line 28: / Line 28: @@
 **Antennas**
+\\ de SA6KRZ
+Updated 2026-03-02
 In this segment, possible exam questions have been marked //**POSSIBLE EXAM QUESTIONS**//.
@@ Line 82: / Line 85: @@
   * Polarisation and x-pol suppression
-Many of these parameters can be analysed using a vector network analyser or an antenna analyser. (Let's do that at ETA?)
+Many of these parameters can be analysed using a vector network analyser or an antenna analyser.
 \\
@@ Line 111: / Line 114: @@
 \\
-== Lobes (SE: Lober) ==
+== Lobes (SE: Strålkäglor) ==
-Important: almost always, antennas do not emit/receive in a single direction. Most antennas emit/receive in one "very good" direction, and a small set of "less good but OK" directions. How well an antenna is emitting to a particular direction, is known as a //lobe// (SE: lob).
+Important: almost always, antennas do not emit/receive in a single direction. Most antennas emit/receive in one "very good" direction, and a small set of "less good but OK" directions. How well an antenna is emitting to a particular direction, is known as a //lobe// (SE: strålkägla).
-The direction with the highest directivity of the antenna, is known as the //main lobe// (SE: huvudloben). Thus, the smaller lobes are known as //sidelobes// (SE: sidolober). The main lobe in practice defines which way the antenna is pointing.
+The direction with the highest directivity of the antenna, is known as the //main lobe//. Thus, the smaller lobes are known as //sidelobes//. The main lobe defines which way the antenna is pointing, both by convention and often in practice.
 Simple antennas, like a monopole antenna, only have a single lobe. Very complex antennas, may have lobes that are shaped practically in any way imaginable. Example: an antenna in a satellite orbiting above a nation, might have an antenna with a lobe pattern (SE: strålningsdiagram) that is shaped according to the borders of that nation. The antenna is thus good at transmitting/receiving to/from that nation, and worse at transmitting/receiving to/from locations outside of that nation's borders. In practice, it is very hard to design an antenna with such a complicated lobe pattern. Companies approach this problem for instance using evolutional AI algorithms that brute-force designs until the lobe pattern is achieved. Another very common approach, is to make a very large array of antennas, and control the phase of the signal reaching each antenna, in order to achieve a more complicated lobe pattern.
+A different example is the antenna running along the edge of your smartphone, disguised as a metal border rim. Having such a weird shape allows for a very high bandwidth, but the antenna must be paired with an always-on autotuner inside the phone for matching.
@@ Line 139: / Line 144: @@
 \\
 ==How wide is a lobe?==
-Stand in front of a transmitting antenna with a power detector. Assume that the strongest power in the main lobe is denoted P. As you move to the side, you see the power going down. The point at which the power has dropped 3 dB, is known as the -3 dB point (SE: halvvärdesbredd). By convention, the lobe is said to end at this point. Even though there is some power being transmitted beyond that point, as you move to the side further. Another (less common) datasheet specification, is also the -10 dB point.
+Stand in front of a transmitting antenna with a power detector. Assume that the strongest power in the main lobe is denoted P. As you move to the side, you see the power going down. The point at which the power has dropped 3 dB, is known as the //-3 dB point// (SE: halvvärdesbredd). By convention, the lobe is said to end at this point. Even though there is some power being transmitted beyond that point, as you move to the side further. Another (less common) datasheet specification, is also the -10 dB point.
 \\
-Now, let's assume that you've found the -3 dB points to the left and to the right of the main lobe. If you draw a triangle between these two points and the antenna, you'll create some angle α at point of the triangle (at the antenna). This angle is known as the //beamwidth// of the lobe (SE: öppningsvinkel).\\
+Now, let's assume that you've found the -3 dB points to the left and to the right of the main lobe. If you draw a triangle between these two points and the antenna, you'll create some angle α at apex point of the triangle (at the antenna). This angle is known as the //beamwidth// of the lobe (SE: öppningsvinkel).\\
 \\
@@ Line 178: / Line 183: @@
 Size-wise, antenna //elements// are usually 0.25 · λ or 0.5 · λ in length/size. An antenna with several elements of different lengths, can usually operate fairly well across a span of frequencies.
-//Why have I never seen an antenna that is 1.0 · λ in length?//
-\\
-A full-wave antenna is by definition resonant. A positive voltage on the antenna is cancelled by a negative voltage on the antenna. No field leaves the antenna. It's gain is thus 0; it doesn't work.
@@ Line 198: / Line 198: @@
-==Velocity factor (SE: förkortningsfaktor)==
+==Realistic design factors (SE: förkortningsfaktor)==
-Light travels slower in various media. Fact is that antenna component dimensions have to be scaled with the velocity factor in the relevant media. Often, you may see that some factor is given as 0.95, 0.96 or 0.98 etc. For instance, aluminium tubing typically has a factor of 0.96.
+Antenna component dimensions have to be scaled down when making real antennas. There are various factors that all make up a 0-1 scaling factor, that effectively makes it so that your antenna is shorter than what it would have been if you only accounted for the wavelength of some frequency. Often, you may see that some factor is given as 0.95, 0.96 or 0.98 etc. For instance, aluminium tubing typically has a factor of 0.96.
 \\
 //**POSSIBLE EXAM QUESTION**//
 \\
-You are building a full-wavelength delta-loop antenna for 7.1 MHz. The wire has a velocity factor of 0.95. How much wire will you use in total?
+You are building a full-wavelength delta-loop antenna for 7.1 MHz. The wire has a scaling factor of 0.95. How much wire will you use in total?
   * 20.07 m
@@ Line 214: / Line 214: @@
 Answer: ( 300 / (1.0 · 7.1) ) · 0.95 = 40.14 m
 \\
-Whether full-wavelength antennas are a good idea or not is irrelevant, that was not part of the question.
 \\
@@ Line 233: / Line 232: @@
 ==Polarisation==
-All antennas emit/receive EM waves. Meaning, that the antenna emits electric and magnetic fields. By convention, the orientation of the //electric// field is said to define the //polarisation// of the antenna. Example: let's say that the antenna is //vertically// polarised, then that would mean that the E-field is sent from the antenna like a sine wave moving up (and down) along the Z-axis, i.e. vertically with respect to the ground. Vice versa, //horisontal// polarisation means that the E-field is propagating like a sine wave that is laying down flat with respect to the ground.
+All antennas emit/receive EM waves. Meaning, that the antenna emits electric and magnetic fields. By convention, the orientation of the //electric// field is said to define the //polarisation// of the antenna. Example: let's say that the antenna is //vertically// polarised, then that would mean that the E-field is sent from the antenna like a sine wave moving up (and down) along the Z-axis, i.e. vertically with respect to the ground. Vice versa, //horizontal// polarisation means that the E-field is propagating like a sine wave that is laying down flat with respect to the ground.
-Very often, it's fully possible to just look an an antenna, and figure out its polarisation. "Which way are the antenna elements pointing?"
+Very often, it's fully possible to simply look an an antenna, and figure out its polarisation. "Where are the antenna elements pointing?"
 Why polarisation is important: typically, the best transmission efficiency between two antennas, is achieved when their polarisations are matching.
@@ Line 253: / Line 252: @@
 \\
 == Antenna impedance matching ==
-Different antenna types have different ideal input impedances. And, the the input impedance is typically frequency dependent. For instance, a given antenna may look like a 50 ohm impedance at 5 MHz, but may look more like an open circuit at 10 MHz.
+Different antenna types have different ideal input impedances. And, the the input impedance is typically frequency dependent. For instance, a given antenna may look like a 50 Ω impedance at 5 MHz, but may look more like an open circuit at 10 MHz.
-Example: the ideal dipole antenna has a 73 ohm input impedance. Feeding this antenna with a coaxial cable of 50 ohm characteristic impedance, leads to a 50 ohm -> 73 ohm impedance interconnect. This impedance difference will result in signal reflections, which are unwanted for several reasons.
+Example: the ideal dipole antenna has a 73 Ω input impedance. Feeding this antenna with a coaxial cable of 50 Ω characteristic impedance, leads to a 50 Ω -> 73 Ω impedance interconnect. This impedance difference will result in signal reflections, which are unwanted for several reasons.
 Overcoming impedance differences in antennas may for instance be done using matching networks.
@@ Line 320: / Line 319: @@
 https://www.youtube.com/watch?v=JHSPRcRgmOw&ab_channel=GerryTrenwith
+Vocabulary
+^ English ^Svenska ^ Comment ^
+| Resistor     | Motstånd       | |