{"id":96636,"date":"2020-10-13T07:42:45","date_gmt":"2020-10-13T05:42:45","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/opredelyaem-napravlenie-na-aeroport-s-pomoshhyu-rtl-sdr-i-gnu-radio"},"modified":"2020-10-13T07:42:45","modified_gmt":"2020-10-13T05:42:45","slug":"opredelyaem-napravlenie-na-aeroport-s-pomoshhyu-rtl-sdr-i-gnu-radio","status":"publish","type":"post","link":"https:\/\/prohoster.info\/ro\/blog\/administrirovanie\/opredelyaem-napravlenie-na-aeroport-s-pomoshhyu-rtl-sdr-i-gnu-radio","title":{"rendered":"Determin\u0103m direc\u021bia c\u0103tre aeroport folosind RTL-SDR \u0219i GNU Radio","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Salut, Habr!<\/p>\n

\u00cen prezent, nu exist\u0103 at\u00e2t de multe standarde de comunicare care, pe de-o parte, s\u0103 fie interesante \u0219i curioase, iar pe de alt\u0103 parte, descrierea lor s\u0103 nu ocupe 500 de pagini \u00een format PDF. Unul dintre acestea, u\u0219or de decodat, este semnalul VHF Omni-directional Radio Beacon (VOR), utilizat \u00een aeronautic\u0103.<\/p>\n

\"Determin\u0103m
\nVOR Beacon (c) wikimedia.org<\/i><\/p>\n

Pentru \u00eenceput, o \u00eentrebare pentru cititori - cum se poate forma un semnal astfel \u00eenc\u00e2t, folosind o anten\u0103 de recep\u021bie omnidirec\u021bional\u0103, s\u0103 se poat\u0103 determina direc\u021bia? R\u0103spunsul este mai jos.
\n<\/a><\/noindex><\/p>\n

Informa\u021bii generale<\/h2>\n

\nSistem Very High Frequency Omni-directional Range<\/a><\/noindex> (VOR) este folosit \u00een aeronautic\u0103 \u00eenc\u0103 din anii '50 ai secolului trecut \u0219i const\u0103 din radiomaiacuri de relativ scurt\u0103 distan\u021b\u0103 (100-200 km), care func\u021bioneaz\u0103 \u00een intervalul de frecven\u021be VHF 108-117 MHz. Acum, \u00een era gigaher\u021bilor, denumirea de very high frequency aplicabil\u0103 acestor frecven\u021be sun\u0103 amuzant \u0219i deja sugereaz\u0103 v\u00e2rsta<\/i> acestui standard, dar, de altfel, mai func\u021bioneaz\u0103 mai multe radiomaia NDB<\/a><\/noindex>, care opereaz\u0103 \u00een intervalul mediilor de und\u0103 400-900 kHz. <\/p>\n

Amplificarea antenei direc\u021bionate pe avion este construc\u021bional incomod\u0103, a\u0219a c\u0103 a ap\u0103rut problema cum s\u0103 codific\u0103m informa\u021bia despre direc\u021bia spre radiomaiac chiar \u00een semnal. Principiul de func\u021bionare poate fi explicat \u00een termeni simpli. Imagina\u021bi-v\u0103 c\u0103 avem un radiomaiac obi\u0219nuit, care trimite un fascicul \u00eengust de lumin\u0103 verde, ale c\u0103rui lampi se rotesc o dat\u0103 pe minut. Este evident c\u0103, o dat\u0103 pe minut, vom vedea o fulgerare de lumin\u0103, dar o astfel de fulgerare nu poart\u0103 multe informa\u021bii. S\u0103 ad\u0103ug\u0103m radiomaia omnidirec\u021bionat\u0103<\/i> o lamp\u0103 de culoare ro\u0219ie, care p\u00e2lp\u00e2ie \u00een momentul \u00een care fasciculul farului \"trece\" \u00een direc\u021bia nord. Deoarece perioada de fulgere \u0219i coordonatele farului sunt cunoscute, calcul\u00e2nd \u00eent\u00e2rzierea \u00eentre fulgerile ro\u0219ie \u0219i verde, putem determina azimutul fa\u021b\u0103 de nord. Totul este simplu. R\u0103m\u00e2ne s\u0103 facem acela\u0219i lucru, dar cu ajutorul radio. Acest lucru a fost rezolvat prin modificarea fazelor. Pentru transmitere sunt utilizate dou\u0103 semnale: faza primului este constant\u0103 (referin\u021b\u0103), iar faza celui de-al doilea (variabil\u0103) se schimb\u0103 \u00eentr-un mod complex \u00een func\u021bie de direc\u021bia radia\u021biei - fiec\u0103rui unghi \u00eei corespunde un anumit decalaj de faz\u0103. Astfel, fiecare receptor va primi semnalul cu \"decalajul\" s\u0103u de faz\u0103, propor\u021bional cu azimutul c\u0103tre far. Tehnologia \u201emodula\u021biei spa\u021biale\u201d se realizeaz\u0103 cu ajutorul unei antene speciale (Alford Loop, vezi KDPV) \u0219i a unei modula\u021bii destul de ingenioase. Aceasta este, de fapt, tema acestui articol.<\/p>\n

S\u0103 ne imagin\u0103m c\u0103 avem un far legacy obi\u0219nuit, care func\u021bioneaz\u0103 din anii '50 \u0219i transmite semnale \u00een modulare AM obi\u0219nuit, folosind Alfabetul Morse. Probabil, c\u00e2ndva, navigatorul asculta cu adev\u0103rat aceste semnale \u00een c\u0103\u0219ti \u0219i marca direc\u021biile cu un rigl\u0103 \u0219i un compas pe hart\u0103. Vrem s\u0103 ad\u0103ug\u0103m func\u021bii noi semnalului, dar f\u0103r\u0103 a \"p\u0103ru s\u0103\" compatibilitatea cu cele vechi. Tema este familiar\u0103, nimic nu e nou... A fost realizat \u00een felul urm\u0103tor - semnalului AM i s-a ad\u0103ugat un ton de frecven\u021b\u0103 joas\u0103 de 30 Hz, care serve\u0219te ca semnal de faz\u0103 de referin\u021b\u0103, \u0219i o component\u0103 de frecven\u021b\u0103 \u00eenalt\u0103, codificat\u0103 prin modulare de frecven\u021b\u0103 la 9.96 kHz, care transmite semnalul de faz\u0103 variabil\u0103. Separ\u00e2nd cele dou\u0103 semnale \u0219i compar\u00e2nd fazele, ob\u021binem unghiul dorit de la 0 la 360 de grade, care este azimutul necesar. Totodat\u0103, toate acestea nu vor \u00eempiedica ascultarea farului \u201e\u00een mod obi\u0219nuit\u201d \u0219i r\u0103m\u00e2ne compatibil cu vechile receptoare AM. <\/p>\n

Trecem de la teorie la practic\u0103. S\u0103 pornim receptorul SDR, s\u0103 alegem modularea AM \u0219i o l\u0103\u021bime de band\u0103 de 12 kHz. Frecven\u021bele farurilor VOR pot fi u\u0219or g\u0103site online. Pe spectru, semnalul arat\u0103 astfel:<\/p>\n

\"Determin\u0103m
\n
\n\u00cen acest caz, semnalul farului este transmis la o frecven\u021b\u0103 de 113.950 MHz. La mijloc se vede o linie de modula\u021bie a amplitudinii u\u0219or de recunoscut \u0219i semnale \u00een cod Morse (.- \u2014 \u2026 care \u00eenseamn\u0103 AMS, Amsterdam, aeroportul Schiphol). \u00cen jur, la o distan\u021b\u0103 de 9.6 kHz de purt\u0103tor, se v\u0103d dou\u0103 v\u00e2rfuri care transmit semnalul secundar. <\/p>\n

S\u0103 \u00eenregistr\u0103m semnalul \u00een format WAV (nu MP3 \u2014 compresia cu pierderi va distruge \u00eentreaga structur\u0103 a semnalului) \u0219i s\u0103-l deschidem \u00een GNU Radio.<\/p>\n

Decodare<\/h2>\n

\nPasul 1<\/b>. Vom deschide fi\u0219ierul cu semnalul \u00eenregistrat \u0219i aplic\u0103m un filtru de frecven\u021be joase pentru a ob\u021bine primul semnal de referin\u021b\u0103. Graficul GNU Radio este prezentat \u00een imagine.<\/p>\n

\"Determin\u0103m
\n
\nRezultatul: semnal de frecven\u021b\u0103 joas\u0103 cu o frecven\u021b\u0103 de 30 Hz.<\/p>\n

\"Determin\u0103m
\n
\nPasul 2<\/b>: decodific\u0103m semnalul de faz\u0103 variabil\u0103. A\u0219a cum am men\u021bionat anterior, acesta se afl\u0103 la frecven\u021ba de 9,96 kHz, trebuie s\u0103-l mut\u0103m la frecven\u021ba zero \u0219i s\u0103-l trimitem la demodulatorul FM.<\/p>\n

Graficul GNU Radio:<\/p>\n

\"Determin\u0103m
\n
\nTotul este rezolvat. Vedem dou\u0103 semnale, diferen\u021ba de faz\u0103 a c\u0103rora indic\u0103 unghiul dintre receptor \u0219i farul VOR:<\/p>\n

\"Determin\u0103m
\n
\nSemnalul este destul de zgomotos \u0219i pentru calculul final al diferen\u021bei de faz\u0103 poate fi necesar\u0103 filtrarea suplimentar\u0103, dar sper c\u0103 principiul este clar. Pentru cei care au uitat cum se determin\u0103 diferen\u021ba de faz\u0103, imaginea din aviation.stackexchange.com<\/a><\/noindex>:<\/p>\n

\"Determin\u0103m
\n
\nDin fericire, nu trebuie s\u0103 facem toate acestea manual: exist\u0103 deja un proiect gata<\/a><\/noindex> \u00een Python, care decodific\u0103 semnalele VOR din fi\u0219iere WAV. De fapt, studiul acestuia m-a inspirat s\u0103 cercetez acest subiect.<\/p>\n

Cei interesa\u021bi pot rula programul \u00een consol\u0103 \u0219i ob\u021bine unghiul \u00een grade dintr-un fi\u0219ier deja \u00eenregistrat:<\/p>\n

\"Determin\u0103m
\n
\nPasiona\u021bii de avia\u021bie pot chiar s\u0103 \u00ee\u0219i construiasc\u0103 un receptor portabil din RTL-SDR \u0219i Raspberry Pi. Apropo, pe un avion \u201eadev\u0103rat\u201d, acest indicator arat\u0103 cam a\u0219a:<\/p>\n

\"Determin\u0103m
\nImagine © www.aopa.org<\/a><\/noindex><\/p>\n

Concluzie<\/h2>\n

\nAstfel de semnale \u201edin secolul trecut\u201d sunt cu siguran\u021b\u0103 interesante pentru analiz\u0103. \u00cen primul r\u00e2nd, sunt destul de simple, DRM-ul modern sau, cu at\u00e2t mai mult, GSM-ul, nu pot fi decodificate at\u00e2t de simplu. Ele sunt deschise pentru recep\u021bie, nu au chei \u0219i criptografie. \u00cen al doilea r\u00e2nd, este posibil ca \u00een viitor ele s\u0103 dispar\u0103 \u00een istorie \u0219i s\u0103 fie \u00eenlocuite de naviga\u021bia prin satelit \u0219i sisteme digitale mai moderne. \u00cen al treilea r\u00e2nd, studiul acestor standarde permite descoperirea unor detalii tehnice \u0219i istorice interesante despre modul \u00een care problemele au fost rezolvate \u00een trecut cu alte scheme \u0219i baze de elemente. A\u0219adar, posesorilor de receptoare li se poate recomanda s\u0103 primeasc\u0103 aceste semnale, c\u00e2t timp \u00eenc\u0103 func\u021bioneaz\u0103.<\/p>\n

Ca de obicei, tuturor experimente reu\u0219ite.
\n
Sursa: habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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