vreau sa fac emitator pe 26Khz

[Vizitator sharckdj]

As vrea sa stiu si eu daca se poate construi un emitator pe frecventa de 26Khz si daca da as fi recunoscator daca m-ar ajuta cineva cu niste scheme sau documentatii.Va multumesc!

[radu25]

In principiu se poate, dar cred ca va fi antena cam mare.

[mircea888]

Eu nu ma pricep prea mult la radio dar stiam ca frecventa purtatoare(modulata) trebuie sa fie de cateva ori mai mare decat aia modulatoare.

[yo9hrb]

Poate nu o moduleaza.

[radu25]

Eu nu ma pricep prea mult la radio dar stiam ca frecventa purtatoare(modulata) trebuie sa fie de cateva ori mai mare decat aia modulatoare.

Trebuie sa fie de cel putin doua ori mai mare. Asadar, daca modulezi cu un spectru de 300Hz -10KHz ar merge. Sau poate omul moduleaza in amplitudine. Oricum, ar trebui o antena de cativa kilometri.Cred ca vroia sa spuna 26Mhz. In cazul asta ar fi mai bine 27MHz cu maxim 4W. Pt 27 se gasesc statii gata facute la preturi mici.

[mircea888]

am uitat de modularea in amplitudine :rolleyes: am inteles ca antena trebuie sa fie foarte mare (din cauza lungimii de unda) dar stiam ca frecventele joase nu pot transporta multa energie, deci nu pot fi folosite in transmitatoare radio. nu ma pricep prea mult dar poate mai invat ceva.

[radu25]

As vrea sa stiu si eu daca se poate construi un emitator pe frecventa de 26Khz si daca da as fi recunoscator daca m-ar ajuta cineva cu niste scheme sau documentatii.Va multumesc!

De curiozitate!?Ce vrei sa emiti si cine te receptioneaza pe frecventa asta?Numai submarinele comunica pe frecventa asta.

[Stefan]

cum naiba comunica submarinele in aceasta frecventa ca nu sunt balene (parca astea emit ultrasunete in apa??) Sigur a gresit , trebuia 26-27 MhzSau poate are un prieten liliac... :yawinkle:

[radu25]

cum naiba comunica submarinele in aceasta frecventa ca nu sunt balene (parca astea emit ultrasunete in apa??) Sigur a gresit , trebuia 26-27 MhzSau poate are un prieten liliac... :yawinkle:

Cam asa!Electromagnetic waves in the ELF frequency range (see also SLF) can travel through the oceans and reach submarines anywhere. Building a ELF transmitter is a formidable challenge, as they have to work at incredibly long wavelengths: The US Navy's system (called Seafarer) operates at 76 hertz, the Soviet/Russian system (called ZEVS) at 82 hertz. The latter corresponds to a wavelength of 3658.5 kilometers. That is more than a quarter of the Earth's diameter. Obviously, the usual half-wavelength dipole antenna cannot be constructed, as it would spread across a large country.Instead, one has to find an area with very low ground conductivity (a requirement opposite to usual radio transmitter sites) and bury two huge electrodes in the ground at different sites separated by about 60 km, and feed lines (wires on poles) to them from a station in the middle. Although other separations are possible, 60 km is the distance used by the ZEVS transmitter located near Murmansk. As the ground conductivity is poor, the current between the electrodes will penetrate deep into the the Earth, essentially using a large part of the globe as antenna. The antenna is very inefficient. To drive it, a dedicated power plant seems to be required, although the power emitted as radiation is only a few watts. Its transmission can be received virtually anywhere. A station in Antarctica noticed when the Russian Navy put their ZEVS antenna into operation.Due to the technical difficulty of building an ELF transmitter, only the US and the Russian Navy owned such systems. Until it was dismantled in late September 2004, the American Seafarer system (76 Hz) consisted of two antennas, located at Clam Lake, Wisconsin (since 1977) and at Sawyer Air Force Base near Gwinn, Michigan (since 1980). Before 1977, the Sanguine system was used, placed in the Laurentian Shield in Wisconsin. The Russian antenna (ZEVS, 82 Hz) is installed at the Kola peninsula near Murmansk. It was noticed in the West in the early 1990s. The British Royal Navy once considered building their own transmitter at Glengarry Forest, Scotland, but the project was cancelled.[edit] ELF TransmissionThe method employed was a 64-ary Reed-Solomon, meaning that the alphabet had 64 symbols, each represented by a very long pseudo-random sequence. The entire transmission was then encrypted. The advantages of such a technique are that by correlating multiple transmissions, a message could be completed even with very low signal-to-noise ratios, and because only a very few pseudo-random sequences represented actual message characters, there was a very high probability that if a message was successfully received, it was a valid message (anti-spoofing).Two facts should be noted: First, the communication link is one-way. No submarine could have its own ELF transmitter on board, due to the sheer size of such a device. Attempts to design a transmitter which can be immersed in the sea or flown on an aircraft were soon abandoned.Second, on such low frequency, information can be transmitted very slowly, on the order of a few characters per minute (see Shannon's coding theorem). Although the actual codes used are secret (their meaning only - the transmissions can be received all over the world), it is reasonable to assume that no specific orders are given, but rather commands like "surface and await orders by satellite radio."

[Vizitator sharckdj]

Frecventa nu vreau sa o modulez, sau o pot modula dat cu o frecventa mai joasa pe la 20hz, in principiu vreau sa generez o frecventa de 26 Khz cu o putere de aproximativ 1W

[yo9hrb]

Teoretic se poate, dar, daca tot ai deschis discutia, ai mila si spune-ne, la ce-ti trebuie? Nu de alta, dar nu mai dorm de vreo 2 zile :partyman: . Mai e undeva o discutie despre frecventele astea, daca nu ma insel ori a deschis-o ori a participat userul dalu364.

[Vizitator sharckdj]

Teoretic se poate ....... dar practic......... m-ar pute ajuta cineva co o scema de oscilator pe acea fercventa cu tuburi sau cu tranzistori........... secretul .... va veni mai tarziu daca voi obtine ceva indrumari si informatii in realizarea acestui circuit.

[Vizitator sharckdj]

Eu cred ca ori faci misto, ori esti in totala necunostinta de cauza.

Eu cred ca nu e nici una valabila din doua. Nu fac misto si nici nu sunt in necunostinta de cauza, probabil crezi asta ca abia mi-am facut cont pe acest forum dar nu e asa. Am sa va dau mai multe detalii despre folosirea lui atunci cand o sa fie in stare de functionare.o zi buna!

[cirip]

Probabil ca a doua... si nu are nici o legatura cu faptul ca esti recent inregistrat. Bun venit!Ca sa scoti 1W in 26KHz nu e nici o filozofie. Problema reala e cu ce radiezi wattul ala. Ce impedanta are radiatorul? Cat de stabil tre sa fie emitatorul? Ca sa poti sa impingi 1W in ceva care radiaza, trebuie sa transformi impedanta la ceva rezistiv, altfel tot ce bagi se reflecta inapoi.Ca emitator se poate folosi un 555 care da intr-un tranzistoras mai tzapan, dar revenim la impedante. Una e sa bagi 1W in 10 ohmi si alta e sa-i bagi 1n 10KOhmi. De asemenea, de la ce tensiune? Sunt o gramada de detalii. Nu orice schema pe care scrie 1W inseamna ca si scoate 1W. Dar fara detalii... e greu sa te ajute cineva. Nu cumva vrei sa comunici pe retea? A, si ce vrei sa radiezi? Acustic sau unda electromagnetica? Vezi cate detalii lipsesc?Cirip

[Vizitator]

secretul .... va veni mai tarziu daca voi obtine ceva indrumari si informatii in realizarea acestui circuit.

"Nu exista nimic care sa nu fi fost descoperit inaintea noastra, inclusiv P4" :yawinkle: Evanghelia dupa dalu364 :partyman: