user:kurser:ham_vt2023_l7
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user:kurser:ham_vt2023_l7 [2023/04/24 19:08] – user | user:kurser:ham_vt2023_l7 [2024/02/13 18:08] (current) – user | ||
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=====ETA313-07: | =====ETA313-07: | ||
- | [[user: | + | [[user: |
**Recommended reading: KonCEPT page 191-229 (chapter 7 + 8) ** | **Recommended reading: KonCEPT page 191-229 (chapter 7 + 8) ** | ||
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* Polarisation and x-pol suppression | * Polarisation and x-pol suppression | ||
- | Many of these parameters can be analysed using a vector network analyser or an antenna analyser. | + | Many of these parameters can be analysed using a vector network analyser or an antenna analyser. |
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==How wide is a lobe?== | ==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, | + | 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, |
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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 // | 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 // | ||
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Size-wise, antenna // | Size-wise, antenna // | ||
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- | //Why have I never seen an antenna that is 1.0 · λ in length?// | ||
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- | 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' | ||
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- | ==Velocity factor | + | ==Realistic design factors |
- | Light travels slower in various media. Fact is that antenna | + | Antenna |
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// | // | ||
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- | You are building a full-wavelength delta-loop antenna for 7.1 MHz. The wire has a velocity | + | You are building a full-wavelength delta-loop antenna for 7.1 MHz. The wire has a scaling |
* 20.07 m | * 20.07 m | ||
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Answer: ( 300 / (1.0 · 7.1) ) · 0.95 = 40.14 m | Answer: ( 300 / (1.0 · 7.1) ) · 0.95 = 40.14 m | ||
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- | Whether full-wavelength antennas are a good idea or not is irrelevant, that was not part of the question. | ||
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user/kurser/ham_vt2023_l7.1682363281.txt.gz · Last modified: 2023/04/24 19:08 by user