Nā nīnau hoʻohālike no ke kūkākūkā ʻana i nā nalu lekiō
ʻO nā nalu lekiō kahi ʻano o ka radiation electromagnetic e hana ana i nā kamaʻilio uea ʻole. Me nā alapine (frequencies) mai kekahi mau kilohertz (kHz) a i kekahi mau gigahertz (GHz), hoʻohana ʻia nā nalu lekiō i nā ʻano noi like ʻole—mai nā hoʻolaha lekiō a me ke kīwī a hiki i nā ʻōnaehana kamaʻilio kelepona. Ma kēia ʻatikala, e kūkākūkā mākou i nā hiʻohiʻona o nā nalu lekiō a me kā lākou wehewehe ʻana e kōkua iā mākou e hoʻomaopopo i nā loina a me nā noi o kēia mau nalu i ke ola o kēlā me kēia lā.
Laʻana Nīnau 1: Alapine (frequency) a me ka lōʻihi o ka nalu
Nīnau:
Hoʻouna kahi kikowaena lekiō i nā nalu lekiō ma ke alapine (frequency) o 100 MHz. E helu i ka nalu. (ʻO ka wikiwiki o ke kukui he 3 x 10^8 m/s.)
Kūkākūkā:
Pili ke alapine (f) a me ka nalu (λ) o nā nalu electromagnetic i ka wikiwiki o ka mālamalama (c) ma o ka hoohalike:
\[ c = f \times \lambda \]
Ma hea:
– \( c \) = ka wikiwiki o ka mālamalama (3 x 10^8 m/s)
– \( f \) = alapine (100 MHz a i ʻole 100 x 10^6 Hz)
– \( \lambda \) = ka nalu (e loaʻa)
Mai ke kaulike ma luna, hiki ke helu ʻia ka nalu ma o:
\[ \lambda = \frac{c}{f} \]
No laila:
\[ \lambda = \frac{3 \times 10^8}{100 \times 10^6} = 3 \ \text{mika} \]
No laila, ʻo ka nalu o ke alapine (frequency) o 100 MHz he 3 mika.
Laʻana Nīnau 2: Mana Hoʻoili a me ka Ikaika
Nīnau:
Hoʻopuka kahi mea hoʻoili lekiō 50-watt i nā nalu lekiō isotropically (like ma nā ʻaoʻao āpau). E helu i ka ikaika o nā nalu lekiō ma kahi mamao o 10 mika mai ka mea hoʻoili.
Kūkākūkā:
Hiki ke helu ʻia ka ikaika (I) o kahi nalu i hoʻopuka ʻia e isotropically ma o:
\[ I = \frac{P}{A} \]
Ma hea:
– \( P \) = mana hoʻoili (50 watts)
– \( A \) = ka ʻilikai o ka poepoe (4πr^2)
Ma kahi mamao (r) = 10 mika, ʻo ka ʻili o ka pōpō penei:
\[ A = 4\pi (10)^2 = 400\pi \]
No laila:
\[ I = \frac{50}{400\pi} = \frac{1}{8\pi} \ \text{watt/m}^2 \]
No laila, ʻo ka ikaika o nā nalu lekiō ma kahi mamao o 10 mika mai ka mea hoʻoili ʻo \( \frac{1}{8\pi} \) watt/m².
Laʻana Nīnau 3: Bandwidth a me ke Kaha o ke Kahawai
Nīnau:
He 20 MHz ka bandwidth o ke kahawai kamaʻilio. Inā e hoʻohana ana i ka modulation QPSK (Quadrature Phase Shift Keying), he aha ka mana kiʻekiʻe loa o ke kahawai?
Kūkākūkā:
He ʻehā mau pae like ʻole o ka modulation QPSK, no laila hiki iā ia ke hoʻouna i 2 bits no kēlā me kēia hōʻailona i hoʻokahi manawa.
ʻO ka helu o nā hōʻailona i kekona e hiki ai i kahi bandwidth 20 MHz ke lawelawe:
\[ \text{Symbol} = 20 \times 10^6 \ \text{symbol/kekona} \]
ʻOiai ʻo QPSK e hoʻouna ana i 2 mau bits no kēlā me kēia hōʻailona, ʻo ka mana a i ʻole ka helu o nā bits i kekona (bitrate) penei:
\[ \text{Bitrate} = 20 \times 10^6 \times 2 = 40 \ \text{Mbps} \]
No laila, ʻo ka nui o ka mana o ke kahawai he 40 Mbps.
Laʻana Nīnau 4: Ke Kūʻē a me ka Hoʻopilikia
Nīnau:
ʻIke kahi mea hoʻoili lekiō ma ke alapine (frequency) o 101.1 MHz i nā mea hoʻopilikia mai kekahi mea hoʻoili ʻē aʻe ma ke alapine (frequency) o 101.3 MHz. E helu i ka hopena o ke alapine (frequency).
Kūkākūkā:
ʻO ke alapine kuʻi \( f_{beat} \) hiki mai ma muli o ka ʻokoʻa ma waena o ʻelua mau alapine kokoke a hiki ke helu ʻia e:
\[ f_{beat} = |f_1 – f_2| \]
Ma hea:
– \( f_1 \) = 101.1 MHz
– \( f_2 \) = 101.3 MHz
No laila:
\[ f_{beat} = |101.1 – 101.3| = | -0.2 | = 0.2 \ \text{MHz} \]
No laila, ʻo ka hopena o ke alapine (frequency) he 0.2 MHz.
Laʻana Nīnau 5: Hopena Doppler ma nā Nalu Lekiō
Nīnau:
Hoʻouna kahi kikowaena lekiō ma ke alapine (frequency) o 95 MHz. Hoʻokokoke kahi mokulele i ke kikowaena lekiō ma ka wikiwiki o 340 m/s. E helu i ke alapine (frequency) i loaʻa i ka mokulele inā like ka wikiwiki o nā nalu lekiō me ka wikiwiki o ka mālamalama (3 x 10^8 m/s).
Kūkākūkā:
Hiki ke hōʻike ʻia ka hopena Doppler no nā nalu lekiō penei:
\[ f_{ʻae} = f_{0} \left(\frac{c + v}{c}\ʻākau) \]
Ma hea:
– \( f_0 \) = alapine (pinepine) mua (95 MHz)
– \( v \) = ka wikiwiki o ka mokulele (340 m/s)
– \( c \) = ka wikiwiki o ka nalu (3 x 10^8 m/s)
No laila:
\[ f_{ʻae} = 95 \times 10^6 \left(\frac{3 \times 10^8 + 340}{3 \times 10^8}\right) \]
\[ f_{ʻae} = 95 \times 10^6 \left(\frac{3 \times 10^8 + 3.4 \times 10^2}{3 \times 10^8}\right) \]
\[ f_{ʻae} \approx 95 \times 10^6 \left(1 + \frac{3.4 \times 10^2}{3 \times 10^8}\right) \]
\[ f_{ʻae} \approx 95 \times 10^6 \left(1 + 1.1333 \times 10^{-6}\right) \]
\[ f_{ʻae} \approx 95 \times 10^6 \times 1.0000011333 \]
\[ f_{ʻae} \approx 95.000107 \ \text{MHz} \]
No laila, ʻo ke alapine (frequency) i loaʻa e ka mokulele e hoʻokokoke mai ana ma kahi o 95.000107 MHz.
Pani
He mea nui ka hoʻomaopopo ʻana i nā loina kumu a me nā ʻano helu o nā nalu lekiō ma nā ʻano ʻenekinia a me nā ʻepekema like ʻole. Hāʻawi nā pilikia ma luna nei i kekahi mau laʻana o ke ʻano o ka hoʻopili ʻia ʻana o ka physics nalu lekiō ma nā ʻano hana like ʻole. ʻO ke ala i ka hoʻomaopopo hohonu ʻana ma o ka hoʻomaʻamaʻa mau a me ka ʻimi ʻana i nā noi honua maoli o nā nalu lekiō i ka ʻenehana kamaʻilio a mākou e hoʻohana ai i kēlā me kēia lā.
