A form of interference to received signals that is produced when a mixer responds to a signal frequency equal to the Local Oscillator minus the Intermediate Frequency when the desired signal frequency is equal to the LO + IF. Also when the mixer responds to a signal frequency equal to the LO + IF when the desired signal frequency is the LO - IF.
The opposition to electric current in an ac circuit. Impedance includes factors other than resistance, and applies to alternating currents. Ideally, the characteristic impedance of a feed line is the same as the transmitter output impedance and the antenna input impedance.
A measure of the ability of a coil to store energy in a magnetic field.
Inductor.
An electrical component usually composed of a coil of wire wound on a central core. An inductor stores energy in a magnetic field.
Input Frequency.
A repeater's receiving frequency. To use a repeater, transmit on the input frequency and receive on the output frequency.
Input Impedance.
The load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to its input. For example, an amplifier with 100,000 ohm input impedance looks equivalent to a 100,000 ohm resistor to the device driving it.
Insulator.
A material that maintains a tight grip on its electrons, so that an electric current cannot pass through it (within voltage limits).
Integrated Circuit (IC).
An electronic device with many transistors 'built' inside to reate circuits. Usually a black plastic rectangle or square. Connections to external circuits are made via pins that can either be along one side, two sides, four sides or even underneath.
Intermediate Frequency (IF).
The output frequency of a mixing stage in a superheterodyne receiver. The subsequent stages in the receiver are tuned for maximum efficiency at the IF.
Intermediate Frequency Shift (IF Shift).
A function that electronically shifts IF frequency from a center frequency, helping to eliminate interference.
Distortion within RF circuits made from upper and lower adjacent channel signals.
International Amateur Radio Union (IARU).
An international confederation of national amateur radio organisations that allows a forum for common matters of concern and collectively represents matters to the International Telecommunications Union (ITU). There are 3 regions of the IARU corresponding to the 3 ITU regions. The IARU was formed in 1925.
International Telecommunications Union [The] / ITU.
The ITU is a United Nations Organization that governs the international rules related to all radio operations including Amateur Radio. Member countries of this body meet every two years to discuss frequency allocations and other rules related to radio communication. These meetings are known as WRCs or World Radio Conferences. The main purpose of these frequency allocations is to prevent two users (especially from different services) from using the same frequencies at the same time.
The ITU divides the world into 3 regions:
ITU Region
Area Within Region
1
Europe and Africa
2
North and South America
3
Asia, Australia and Oceania
The three regions have similar but not identical frequency allocations. See also: EHF. HF. MF. SHF. UHF. VHF.
A way of using the internet to join repeaters or simplex stations together. Your RF signal is received by the local gateway radio, fed into a computer, converted to a digital signal, relayed via the Internet, converted back to audio and retransmitted by the remote gateway, this system of passing speech via digital data on the internet is known as VoIP (Voice over Internet Protocol). See also: Digital Modes page.
Internet Protocol (IP).
Data-oriented protocol used for communicating data across a packet-switched internetwork.
Internet Radio Linking Project (IRLP).
A project that links amateur radio stations around the world by using Voice over Internet Protocol (VoIP). Each gateway consists of a dedicated computer running custom software that is connected to both a radio and the Internet. This arrangement forms what is known as an IRLP Node. Since all end users communicate using a radio as apposed to using a computer directly, IRLP has adopted the motto "Keeping the Radio in Amateur Radio". Amateur radio operators within range of a local node are able to use DTMF to initiate a node-to-node connection with any other available node in the world. Each node has a unique 4 digit node number in the range of 1000-8999. Invented by David Cameron, VE7LTD, in 1997. In April 2007, there were over 1,280 nodes across 7 continents. See also: Digital Modes page.
Ionizing Radiation.
Electromagnetic radiation that has sufficient energy to knock electrons free from their atoms, producing positive and negative ions. X-rays, gamma rays and ultraviolet radiation are examples of ionizing radiation.
Ionosphere.
A region of electrically charged (ionized) gases high in the atmosphere. The ionosphere bends radio waves as they travel through it, returning them to Earth. See also: sky-wave propagation.
IOTA .
Islands on the Air. An amateur radio activity designed to encourage contacts with island stations world wide. The oceans' islands have been grouped into some 1200 IOTA groups with, for reasons of geography, varying numbers of 'counters', or qualifying islands, in each. The objective, for the island chaser, is to make radio contact with at least one counter in as many of these groups as possible and, for the DXpeditioner, to provide the island contacts.
