user:kurser:ham_vt2023_l7
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- | 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/ | ||
+ | |||
+ | Reflections cause standing waves and non-optimal power transfer/ | ||
+ | |||
+ | VSWR = Voltage Standing Wave Ratio = Z1/Z2 OR Z2/Z1 so a x:1 relation is formed. | ||
+ | |||
+ | We want to " | ||
+ | |||
+ | Balanced/ | ||
+ | |||
+ | balanced TL folded out -> dipole antenna! Nice SWR achieved. L = lambda/2 = 300/(2*f) ~=(0, | ||
+ | |||
+ | ==Antennas== | ||
+ | |||
+ | Antenna = two port that converts energy from propagating in a transmission line to propagation in free-space. | ||
+ | |||
+ | Characterized by: | ||
+ | * Input impedance, SWR, Z_in | ||
+ | * Operation frequency, resonance frequency, f_0 | ||
+ | * Directivity D, antenna gain, dBi, dBd | ||
+ | * far field distance = d_f > 2*D^2/ | ||
+ | * Radiation efficiency, eta | ||
+ | * radiation pattern, E & H patterns | ||
+ | * Polarization and x-pol suppression and so on... | ||
+ | |||
+ | We can only measure input impedance and operational frequency easily with a VNA/Antena analyzer ... so lets do that at ETA. | ||
+ | |||
+ | Different types | ||
+ | * Dipole | ||
+ | * Monopole | ||
+ | * Small loop | ||
+ | * Yagi | ||
+ | * Quad | ||
+ | * Patch | ||
+ | * Bowtie | ||
+ | * PCB/PIFA | ||
+ | * Spiral/ | ||
+ | |||
+ | Talk about polarization. | ||
+ | |||
+ | Common mode current on coax = bad! | ||
+ | |||
+ | == Propagation == | ||
+ | |||
+ | **HF/short wave** | ||
+ | |||
+ | 1) Ground wave (20-40 km typical) | ||
+ | 2) Space wave (global range) | ||
+ | * Reflections from the ionosphere' | ||
+ | * Reflections affect polarization chaotically. | ||
+ | * D = 60-90 km height. | ||
+ | * " | ||
+ | * Only daytime | ||
+ | * Attenuate <10MHz | ||
+ | * E = 90-110 km | ||
+ | * F = F1 + F2 = 150-350 km - reflection. | ||
+ | * Reflect < | ||
+ | * Created during daytime, slow to unionize | ||
+ | |||
+ | **3.5-7 MHz** | ||
+ | * Attenuated by D | ||
+ | * skyward wave/ | ||
+ | | ||
+ | **14-30 MHz** | ||
+ | * Not really affected by D | ||
+ | * skyward wave/ | ||
+ | * Sporadic-E might enable local connections | ||
+ | |||
+ | DX -> 10 degree max antenna gain is best | ||
+ | |||
+ | **VHF/ | ||
+ | * 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/ | ||
+ | * Reflect signals from big things | ||
+ | |||
+ | **Microwaves** | ||
+ | * Moon/ | ||
+ | * Reflect signals from big things | ||
+ | * Also rain scatter | ||
+ | |||
+ | Fading example with cellphone if possible | ||
+ | |||
+ | |||
+ | Radio Antenna Fundamentals Part 1 1947 | ||
+ | |||
+ | https:// | ||
user/kurser/ham_vt2023_l7.txt · Last modified: 2024/02/13 18:08 by user