''ΕΡΑΣΙΤΕΧΝΙΚΟ ΔΥΚΤΙΟ ΕΛΛΑΔΑΣ ΝΟΣΤΑΛΓΙΑ''
H ΚΑΛΥΤΕΡΗ ΕΛΛΗΝΙΚΗ ΜΟΥΣΙΚΗ ΑΠΟ ΤΑ 1960 ΜΕΧΡΙ ΣΗΜΕΡΑ ΟΛΟ ΤΟ 24ΩΡΟ . Ο ΣΤΑΘΜΟΣ ΤΩΝ ΜΕΓΑΛΩΝ ΕΠΙΤΥΧΙΩΝ ΤΟΥ ΕΛΛΗΝΙΚΟΥ ΠΕΝΤΑΓΡΑΜΟΥ ΣΤΗΝ ΕΛΛΑΔΑ ΜΕ ΕΚΠΛΗΚΤΙΚΗ ΠΟΙΟΤΗΤΑ ΗΧΟΥ HD.
In this article LodeRunner explains
what an Inverted-L antenna is, how it works, and why you might strongly
consider building one for use on the lower bands. While explaining its
use with a high degree of technical information, he’s written it in a
manner that’s easy to follow and digest. The diagram data is sourced
from EZ-NEC, which a link to the software is provided in the sidebar.
The Inverted-L Antenna and NVIS
An
“Inverted-L” antenna is basically a wire antenna, typically ¼ to ½
wavelength long on the band it is designed for. The Inverted-L antenna
is a common antenna for the 160 meter and 80 meter amateur bands, where
typical ¼ wave verticals are impractically tall for most amateurs.
In
the Inverted-L configuration, the first portion of the wire rises
vertically from the feedpoint, and at some height is bent roughly 90
degrees, and then extends horizontally to the unterminated end. The
feedpoint is very close to ground level (typically not more than 3 feet
above ground), and the antenna is worked against a Ground consisting of
one or more ground-rods, and/or a counterpoise consisting of one or more
radial wires – which may be buried, laid directly on the ground, or
suspended above the ground at some low height.
Because
the input impedance of a typical Inverted-L antenna is low, and the
feedpoint is at or very close to ground level, where ground losses are
substantial, it is very important to establish a good ground to work the
antenna against.
Most
of the amateur literature regarding the Inverted-L antenna is focused
on optimizing performance of the Inverted-L antenna for “DX” operation –
that is, high efficiency in radiating its energy in a pattern that is
low in elevation (low Take-off Angle, or ToA) – typically below 30
degrees relative to the horizon – which maximizes the distance to which
communications may be achieved. Effective NVIS communications, on the
other hand, require an antenna which is optimized to produce a pattern
where the majority of the radiated energy has a high ToA pattern –
ideally between 60 and 90 degrees – to provide reliable communications
from zero to several hundred miles.
Fig. 1: DX dipole pattern on 80 Meters
First, lets take a look at the difference between a good “DX Antenna” pattern vs. a good “NVIS Antenna” pattern –
Figure
1 is a diagram of a dipole optimized for DX communications; Figure 2
represents the exact same dipole, but the height has been lowered by
approximately 1/3 wavelength to optimize the antenna pattern for NVIS
communications.
This RF amplifier for FM 88-108 MHz with no tune (broadband) needed to cover all the FM Band. This RF Power amplifier is equiped with the famous Mosfet transistor the BLF245.
Depending on the output power level you are able to provide with your FM synthesizer, you can use or not the 2N3866 driver stage included in this amplifier design.
Boosting the output power of low power FM broadcast band exciters is the goal of the project which was based on Motorola MRF171A MOSFET.
The design of the project is based on a MOSFET device with the advantages of high efficiency, ease of tuning, and high gain. The construction was done in a small aluminum die cast box where coaxial sockets are used for the RF input and output connections. A ceramic feedthrough capacitor bolted in the wall of the box routes the power supply. The techniques of construction gave way to the prevention of RF radiation escaping from the amplifier due to excellent shielding. Significant amount of RF radiation as well as harmonic radiation could be radiated without it and could interfere with other sensitive circuits
Amateur radio came into being after radio waves (proved to exist by Heinrich Rudolf Hertz in 1888) were adapted into a communication system in the 1890s by the Italian inventor Guglielmo Marconi.[6] In the late 19th century there had been amateur wired telegraphers setting up their own interconnected telegraphic systems. Following Marconi's success many people began experimenting with this new form of "wireless telegraphy". Information on "Hertzian wave" based wireless telegraphy systems (the name "radio" would not come into common use until several years later) was sketchy, with magazines such as the November, 1901 issue of Amateur Work showing how to build a simple system based on Hertz' early experiments.[1] Magazines show a continued progress by amateurs including a 1904 story on two Boston, Massachusetts 8th graders constructing a transmitter and receiver with a range of eight miles and a 1906 story about two Rhode Island teenagers building a wireless station in a chicken coop. In the US the first commercially produced wireless telegraphy transmitter / receiver systems became available to experimenters and amateurs in 1905.[1] In 1908, students at Columbia University formed the Wireless Telegraph Club of Columbia University, now the Columbia University Amateur Radio Club. This is the earliest recorded formation of an amateur radio club, collegiate or otherwise.[7] In 1910, the Amateurs of Australia formed, now the Wireless Institute of Australia.
RMS Titanic (April 2, 1912).
The rapid expansion and even "mania" for amateur radio, with many thousands of transmitters set up by 1910, led to a wide spread problem of inadvertent and even malicious radio interference with commercial and military radio systems. Some of the problem came from amateurs using crude spark-transmitters that spread signals across a wide part of the radio spectrum.[1] In 1912 after the RMS Titanic sank, the United States Congress passed the Radio Act of 1912[8] which restricted private stations to wavelengths of 200 meters or shorter (1500 kHz or higher).[9] These "short wave" frequencies were generally considered useless at the time, and the number of radio hobbyists in the U.S. is estimated to have dropped by as much as 88%.[10] Other countries followed suit and by 1913 the International Convention for the Safety of Life at Sea was convened and produced a treaty requiring shipboard radio stations to be manned 24 hours a day. The Radio Act of 1912 also marked the beginning of U.S. federal licensing of amateur radio operators and stations. The origin of the term "ham", as a synonym for an amateur radio operator, was a taunt by professional operators.[11][12][13]
