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user:kurser:ham_vt2023_l7 [2026/03/22 17:34] – Language edits lokauser:kurser:ham_vt2023_l7 [2026/03/22 18:34] (current) – Updated Swedish glossary. loka
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 characterized by: Characteristic impedance, Z_0, a geometry and material parameter. Length and the speed of light in the transmission line. Two metal conductors that guide the fields.  characterized by: Characteristic impedance, Z_0, a geometry and material parameter. Length and the speed of light in the transmission line. Two metal conductors that guide the fields. 
  
-Used for high frequency signals. Lambda = 300/f [MHz], Lambda similar to length in size. +Used for high frequency signals. λ = 300/f [MHz], λ similar to length in size. 
  
 Waves propagate along transmission lines. Reflections along a TL are similar to light in a glass/water. Explain transmission/reflection coefficients.  Waves propagate along transmission lines. Reflections along a TL are similar to light in a glass/water. Explain transmission/reflection coefficients. 
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 Balanced/unbalanced (differential/single-ended) TL are important and difficult. Explain this in detail.   Balanced/unbalanced (differential/single-ended) TL are important and difficult. Explain this in detail.  
  
-balanced TL folded out -> dipole antenna! Nice SWR achieved. L = lambda/2 = 300/(2*f) ~=(0,96*lambda/2)+balanced TL folded out -> dipole antenna! Nice SWR achieved. L = λ/2 = 300/(2*f) ~=(0,96*λ/2)
  
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 ... however, in practice there is nothing prohibiting an antenna array from being built using any antenna type. ... however, in practice there is nothing prohibiting an antenna array from being built using any antenna type.
  
-Very often, specific antennas are are combination of other antenna types. For example, the very common Yagi-Uda antenna, is usually built using a combination of three (or more) dipole antennas, and one magnetic loop antenna.+Very often, specific antennas are are combination of other antenna types. For example, the very common Yagi-Uda antenna, is usually built using a combination of three (or more) dipole antennas, and an additional "folded" dipole antenna.
  
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   * Directivity, D, dBi, dBd   * Directivity, D, dBi, dBd
   * Antenna gain   * Antenna gain
-  * Far-field distance = d_f > 2*D^2/λ, given d_f >> D, d_f >> λ+  * Far-field distance = d_f > 2·(L_D)²/λ, given d_f >> L_D, d_f >> λ. Where, L_D is the aperture ≈ largest physical part of the antenna.
   * Radiation efficiency, η   * Radiation efficiency, η
   * Radiation pattern, E & H patterns   * Radiation pattern, E & H patterns
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 These elements are often mounted to a frame of sorts, like a large metal bar that supports all elements. This bar is known as the //boom// (SE: bom). These elements are often mounted to a frame of sorts, like a large metal bar that supports all elements. This bar is known as the //boom// (SE: bom).
  
-Often, antennas are shielded from the evil world of rain, snow, pidgeons etc. by placing them inside a plastic cover shell. This cover shell is known as a //radome// (SE: radom).+Often, antennas are shielded from the evil world of rain, snow, pigeons etc. by placing them inside a plastic cover shell. This cover shell is known as a //radome// (SE: radom).
  
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 ==Direction== ==Direction==
  
-The most ideal antenna is a single charge floating in free space, radiating as a sphere equally strongly in all directions. Such a single charge is known academically as an //isotropic radiator//. Practically, antennas are real objects and thus not single charges, meaning that the "radiation sphere" (made-up word) is very much not a sphere. Most antennas only //illuminate// (actual term) a smaller part of that hypothetical sphere, meaning that most of the EM field is sent/received from/to the antenna at that specific direction in space. The illuminated area is known as the //beam area// (SE: ??).+The most ideal antenna is a single charge floating in free space, radiating as a sphere equally strongly in all directions. Such a single charge is known academically as an //isotropic radiator//. Practically, antennas are real objects and thus not single charges, meaning that the "radiation sphere" (made-up word) is very much not a sphere. Most antennas only //illuminate// (actual term) a smaller part of that hypothetical sphere, meaning that most of the EM field is sent/received from/to the antenna at that specific direction in space. The illuminated area is known as the //beam area// (SE: strålrymdvinkel).
  
 How small that illuminated segment of the sphere is as opposed to size the entire sphere, is known as the //antenna directivity//. The directivity is often given in dB with respect to that ideal //isotropic radiator//. The unit is thus **dBi**. A very large part of an antenna's design specification, is its directivity. Different types of antennas have very different directivities. How small that illuminated segment of the sphere is as opposed to size the entire sphere, is known as the //antenna directivity//. The directivity is often given in dB with respect to that ideal //isotropic radiator//. The unit is thus **dBi**. A very large part of an antenna's design specification, is its directivity. Different types of antennas have very different directivities.
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 Practically, it is not uncommon to describe the directivity of some antenna with respect to something more real. Such as, a dipole antenna's directivity. How much more "directive" (made-up word) is our antenna, in comparison to a dipole antenna? Practically, it is not uncommon to describe the directivity of some antenna with respect to something more real. Such as, a dipole antenna's directivity. How much more "directive" (made-up word) is our antenna, in comparison to a dipole antenna?
  
-A dipole antenna is -2.15 dB less "directive" than an isotropic radiator. Thus, the unit **dBd** = dBi - 2.15.+A dipole antenna is -2.15 dB less "directive" than an isotropic radiator. Thus, the unit **dBd** = dBi -2.15.
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 //dBd = directivity in dB with respect to an ideal dipole antenna.// //dBd = directivity in dB with respect to an ideal dipole antenna.//
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 ==Shaping the lobes + Terminology 2== ==Shaping the lobes + Terminology 2==
-The EM wave that we wish to transmit/receive to the outside world, will travel along a cable into the antenna. Where that cable meets the antenna, is almost always at an antenna element. In a way, you could say that this antenna element is what is in fact transmitting inside of the antenna. This element is known as the //driven// element (SE: drivelement). An antenna may have several driven elements.+The EM wave that we wish to transmit/receive to the outside world, will travel along a cable into the antenna. Where that cable meets the antenna, is almost always at an antenna element. In a way, you could say that this antenna element is what is in fact transmitting inside of the antenna. This element is known as the //driven// element (SE: matat element, aktivt element). An antenna may have several driven elements.
  
 The resulting lobe pattern from the driven element, is then by-design usually deformed using other elements that are in fact not connected to the cable that fed the antenna. All elements on the antenna that are not driving the EM wave, are known as parasitic elements (SE: parasitelement). The resulting lobe pattern from the driven element, is then by-design usually deformed using other elements that are in fact not connected to the cable that fed the antenna. All elements on the antenna that are not driving the EM wave, are known as parasitic elements (SE: parasitelement).
  
-These parasitic elements have different purposes. They could be used to direct the lobe pattern into some wanted direction; such elements are known as //directors// (SE: direktorer). Or, those elements could be to block off the lobe pattern from emitting/receiving into some direction; such elements are known as //reflectors// (SE: reflektorer).+These parasitic elements have different purposes. They could be used to direct the lobe pattern into some wanted direction; such elements are known as //directors// (SE: direktorer, passiva element). Or, those elements could be to block off the lobe pattern from emitting/receiving into some direction; such elements are known as //reflectors// (SE: reflektorer).
  
 Example: the Yagi-Uda antenna, has one driven element on its boom. To get the signal pointing forwards, three dipole directors are mounted at the front of the antenna. And to get the lobe pattern pointing less backwards, a reflector is mounted at its back. Example: the Yagi-Uda antenna, has one driven element on its boom. To get the signal pointing forwards, three dipole directors are mounted at the front of the antenna. And to get the lobe pattern pointing less backwards, a reflector is mounted at its back.
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-==Emitted power: p.e.p. and e.i.r.p==+==Emitted power: p.e.p., e.r.p. and e.i.r.p==
 The HAM radio band plan sets radiation emission limits in terms of power, either as **p.e.p.** or **e.i.r.p.** (peak emitted power, equivalent isotropic radiated power). The HAM radio band plan sets radiation emission limits in terms of power, either as **p.e.p.** or **e.i.r.p.** (peak emitted power, equivalent isotropic radiated power).
  
   * The p.e.p. limit defines how much peak power may be fed into your antenna.   * The p.e.p. limit defines how much peak power may be fed into your antenna.
-  * The e.i.r.p. limit takes antenna gain into account as well, meaning that no lobe may peak above a certain power.+  * The e.r.p. limit takes antenna gain into account as well, where gain = the best gain you get from that antenna, meaning that no lobe may peak above a certain power. 
 +  * The e.i.r.p. limit assumes that your are using a theoretically perfect isotropic radiator as an antenna. So, from a given limit, divide by the gain you would get from an isotropic radiator -> gives you the maximum power you may feed your antenna. 
 + 
 +All power limits allow for subtracting a known loss in the cable, filters etc. before power hits the actual antenna input.
  
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 //**POSSIBLE EXAM QUESTION**// //**POSSIBLE EXAM QUESTION**//
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-In the 5.3515-5.3665 MHz band, a HAM radio operator may at most transmit with 15 W e.i.r.p. Are you allowed to transmit at 5.36 MHz with 10 W using a +3 dB gain directional antenna?+In the 5.3515-5.3665 MHz band, a HAM radio operator may at most transmit with 15 W e.r.p. Are you allowed to transmit at 5.36 MHz with 10 W using a +3 dB gain directional antenna?
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-Answer: No, this is not allowed. An antenna with +3 dB gain, would make a 10 W radiated emission seem as if we're transmitting with 20 W, which is above the e.i.r.p. limit.+Answer: No, this is not allowed. An antenna with +3 dB gain, would make a 10 W radiated emission seem as if we're transmitting with 20 W, which is above the e.r.p. limit.
  
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 All commonly used formulas related to antennas, assume simplifications that happen once we are standing at a large distance away from the antenna. All commonly used formulas related to antennas, assume simplifications that happen once we are standing at a large distance away from the antenna.
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-The far-field distance = d_f > 2*D^2/lambda, given d_f >> D, d_f >> lambda.+The far-field distance = d_f > 2·(L_D²)/λ, given d_f >> L_D, d_f >> λ.
  
 Meaning, that for very high frequencies, our simplifications and thus our formulas, are valid already fairly close to the antenna. The opposite of the far-field is known as the near-field, where most of our formulas stop being valid, and in practice the behaviour of the antenna has to be numerically simulated.  Meaning, that for very high frequencies, our simplifications and thus our formulas, are valid already fairly close to the antenna. The opposite of the far-field is known as the near-field, where most of our formulas stop being valid, and in practice the behaviour of the antenna has to be numerically simulated. 
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 ^ English ^Svenska ^ Comment ^ ^ English ^Svenska ^ Comment ^
 +| -3 dB point     | Halvvärdesbredd       | | 
 +| Antenna array     | Gruppantenn       | | 
 +| Boom     | Bom       | | 
 +| Design factor     | Förkortningsfaktor       | | 
 +| Directors     | Direktorer, passiva element       | | 
 +| Driven element     | Matat element, aktivt element       | | 
 +| Elements     | Antennelement, spröt       | | 
 +| Gain     | Antennvinst       | | 
 +| Lobe     | Strålkägla       | | 
 +| Lobe beamwidth     | Öppningsvinkel       | | 
 +| Lobe pattern     | Strålningsdiagram       | | 
 +| Parasitic element     | Parasitelement       | | 
 +| Radio broadcast     | Rundradio       | | 
 +| Radome     | Radom       | | 
 +| Reflector     | Reflektorer       | | 
 | Resistor     | Motstånd       | |  | Resistor     | Motstånd       | | 
 +
  
user/kurser/ham_vt2023_l7.1774200886.txt.gz · Last modified: 2026/03/22 17:34 by loka