When there is radio interference, whether intentional (jamming) or unintentional, use radio direction finding to track down the source. This is done with a directional antenna or other equipment that gives a bearing to the strongest signal. By taking bearings from two or more different locations and plotting where those bearings intersect, you can pinpoint the location of the interfering transmitter.

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A hidden transmitter hunt (fox hunt) involves a transmitter that sends periodic signals while others try to locate it. The usual and simplest technique is to use a directional antenna and a receiver's signal-strength indication: rotate the antenna and note the direction where the signal is strongest to get a bearing toward the transmitter.

In contrast, a calibrated SWR meter is for tuning an antenna and doesn't provide directional information; it might be useful for antenna setup but not for locating a hidden transmitter. A directional wattmeter measures forward and reflected power and also does not give a direction to the signal source. For finding the fox, the directional antenna (used with an S-meter or separate signal-strength indicator) is the useful tool.

Memory aids / mnemonics:

• Fox hunts = use directionality (directional antenna + signal strength) to get a bearing
• SWR meter = antenna tuning, not direction-finding
• Wattmeter = measures power/return loss, not direction

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Contesting is an operating activity in which operators try to contact as many stations as possible during a specified period. Participants keep a log of their contacts and, rather than having extended conversations, exchange only the minimum information required by the contest rules (typically call signs, signal reports, and a contest exchange) so they can make as many contacts as possible within the time allowed. Contests take place on many amateur bands and can last from a few hours to several days; the emphasis is on rapid, efficient contacts and accumulating points.

• (No memory aids provided.)

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In a contest the goal is to make as many valid contacts as possible in the allotted time. That means you should give the other station only the information needed for proper identification and the contest exchange so they can log you quickly and move on to the next contact. Using only part of your call makes identification unreliable, contacting a station multiple times wastes both stations' time, and adding unnecessary phrases clutters the exchange and slows the station down.

Always be brief, but also be concise and complete.

Memory aids:

• Be brief, concise, and complete.

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A grid locator (often called a Maidenhead grid square or grid square) is a short letter–number code that represents a specific geographic location by encoding latitude and longitude. Amateur radio operators use these grid locators to report where a station is located for contests, awards, propagation studies, and logging. It is a location designator, not a physical instrument or a measurement of azimuth/elevation.

Memory aids:

• Think of a map’s grid: a grid locator tells you where on the map (geographic location) a station is located.

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IRLP: Internet Radio Linking Project

DTMF: Dual-Tone Multi-Frequency

DTMF is the generic term for Touch-Tone. A touch-tone telephone is a DTMF generator — when you press a button it produces a pair of tones. Accessing an IRLP node over the air is done by keying DTMF signals, which can be sent manually from a keypad or generated automatically.

A repeater might also require CTCSS or DCS to access that repeater itself, and some systems require a password to be sent, but the mechanism for controlling IRLP nodes over the air is DTMF signaling.

Memory aids:

• DTMF = Touch-Tone (your phone is a DTMF generator)
• Test tip: "DTMF" has the same number of letters as "IRLP"

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Voice Over Internet Protocol (VoIP) is a way of sending voice communications as digital data over an IP network (the Internet) rather than as an analog audio signal over a traditional telephone or radio link. The audio is digitized, packetized, sent across the network, and reassembled at the far end for playback, so you can carry real‑time conversations using computers, dedicated VoIP phones, or radio systems that interface to the Internet.

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IRLP is one of several projects used for linking repeaters and other amateur radio systems across the internet. It uses Voice over IP (VoIP) to carry the audio between nodes.

Operators send DTMF tones (phone-keypad signals) from a radio to a node to command it to link or unlink with another node or repeater.

Similar systems include EchoLink, AllStar, and Icom's D‑STAR network.

Memory aids (if helpful):

• IRLP = Internet Radio Linking Project — links radios over the Internet

• Think "link" = connect repeaters/nodes together over VoIP

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EchoLink is designed to let an amateur connect to and transmit through an EchoLink-enabled repeater using the EchoLink software on a computer or smartphone. After registering and verifying an account, the user connects over the Internet to the repeater's EchoLink node; audio from the user's device is then sent to the repeater and transmitted on RF, so no local radio is required to initiate the repeater.

Other systems such as IRLP, D-STAR, and DMR have internet-linked capabilities and there are technical ways to access nodes without a local radio, but that practice is generally not the intended or encouraged method for those technologies and is discouraged by many of their maintainers.

Memory aids / practical notes:

• Echo = Repeat(er)
• EchoLink lets you use a smartphone or computer (with a verified EchoLink account) to access EchoLink-enabled repeaters — search "Using Smartphone For EchoLink" for demonstrations.

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EchoLink is a system of Internet-connected stations (including repeaters) that you can access with client software to transmit and receive on amateur radio bands (typically VHF and UHF). Using EchoLink to operate a station is effectively remote control of that station, so when you use it you are the control operator of whichever station you are using.

Because you must be a licensed control operator to operate an amateur station (remote or local), you are required to register your call sign with EchoLink and provide proof of your license before you can use the network. Any licensed amateur may register for an EchoLink account, but registration and proof of license are required.

Keep in mind that you remain responsible for complying with all amateur regulations when using EchoLink. That includes following the rules for the band, IDing, and respecting any additional restrictions when connecting to stations or repeaters in other countries.

EchoLink client software is available for desktop and mobile devices.

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In networking terms, a gateway is a device that connects two different networks; a router is a common type of gateway. Therefore, an amateur station that links a packet radio network to the Internet is called a gateway.

A digipeater is a station that receives digital packets and retransmits them; that repeats packets on the radio network but does not by itself connect to the Internet (though a digipeater could also be configured to act as a gateway). A repeater simultaneously retransmits signals on another frequency and is typically used for voice operation. A beacon transmits information periodically to provide a signal source or propagation information.

Memory aids:

• Gateway = connects networks (think "gateway to the Internet").
• Digipeater = digital repeater (retransmits packets on radio only).
• Repeater = retransmits voice on another frequency.
• Beacon = periodic transmission for info or propagation.

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