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--- user:kurser:ham_vt2023_l7 [2023/02/12 16:56] – user
+++ user:kurser:ham_vt2023_l7 [2023/04/07 12:35] – user
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 [[user:kurser:ham_vt2023|Back to course information]]
-Recommended reading: KonCEPT page 191-229 (chapter 7 + 8)
+**Recommended reading: KonCEPT page 191-229 (chapter 7 + 8) **
+Start with transmission line (TL), the most difficult component.
+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.
+Waves propagate along transmission lines. Reflections along a TL are similar to light in a glass/water. Explain transmission/reflection coefficients.
+Reflections cause standing waves and non-optimal power transfer/losses
+VSWR = Voltage Standing Wave Ratio = Z1/Z2 OR Z2/Z1 so a x:1 relation is formed.
+We want to "match" the antenna, transmission line and radio to minimize losses.
+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)
+==Antennas==
+Show some example antennas.
+  * Ground plane/verticals
+  * Loop antennas
+  * Yagi
+  * log periodic
+  * Parabolic
+  * etc.
+Talk about polarization.
+Common mode current on coax = bad!
+== Propagation ==
+**HF/short wave**
+) Ground wave (20-40 km typical)
+) Space wave (global range)
+    * Reflections from the ionosphere's D, E, F regions. Sunlight ionize the ionosphere.
+    * Reflections affect polarization chaotically.
+    * D = 60-90 km height.
+      * "Dämpningsskiktet" attenuates signals
+      * Only daytime
+      * Attenuate <10MHz
+    * E = 90-110 km
+    * F = F1 + F2 = 150-350 km - reflection.
+      * Reflect <30-50MHz depending on sun activity
+      * Created during daytime, slow to unionize
+**3.5-7 MHz**
+  * Attenuated by D
+  * skyward wave/antenna can reflect back to local contacts (E/F)
+**14-30 MHz**
+  * Not really affected by D
+  * skyward wave/antenna cannot reflect back to local contacts (E/F)
+  * Sporadic-E might enable local connections
+DX -> 10 degree max antenna gain is best
+**VHF/UHF/...**
+  * Penetrates the atmosphere, EME possible
+  * Basically only local line-of-sight connections possible
+  * Troposphere propagation possible. Heat and humidity gradients guide waves. Ex. hearing Danish FM radio in Göteborg.
+  * northern lights reflections >25 MHz. Distorts signals, phone sounds creepy.
+  * Moon/meteor/satellite/airplane scatter
+    * Reflect signals from big things
+**Microwaves**
+  * Moon/meteor/satellite/airplane scatter
+    * Reflect signals from big things
+    * Also rain scatter
+Fading example with cellphone if possible
+Radio Antenna Fundamentals Part 1 1947
+https://www.youtube.com/watch?v=JHSPRcRgmOw&ab_channel=GerryTrenwith