Digital communications methods are methods that send digital information (encoded in bits, 0 or 1) instead of sending an analog signal, such as voice or video.

The methods listed here are all digital modes:

• Packet Radio is probably the best known digital mode which can be thought of as using a modem over a radio to allow computers to exchange data

• JT65 is a digital protocol developed for amateur radio communication with extremely weak signals. It was designed by Joe Taylor, K1JT, to optimize Earth-Moon-Earth (EME) contacts on the VHF bands. The "65" refers to the 65 tones the protocol uses.

• PSK31 is short for Phase Shift Keying, 31 Baud and is more of system for chat over radio; it allows realtime keyboard to keyboard informal chat between operators.

• MFSK is short for Multiple frequency-shift keying and is a variation of FSK, a method used by some packet radio systems.

• IEEE 802.11 is a set of specifications for implementing wireless local area network (WLAN) computer communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands.

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Tags: digital modes section3.7

A talk group on a DMR digital repeater is a way for groups of users to share a channel at different times without being heard by other users on the channel. This is accomplished by ID codes transmitted by the users. Users in a particular group will program their radios with the ID code for their group. Users' radios not programmed to their group's code will remain silent, even while on the same channel.

More in-depth information:

A number of different digital voice radio standards exist including DMR (Digital Mobile Radio) which implements talk groups defined for purposes of the exam as a way for groups of users to share a channel at different times without being heard by other users on the channel. None of the distractors make any sense.

That's all you need to know for this question, but Talk Groups can also be described as the DMR-MARC FAQ does here:

Q. What are Talk Groups?

A. Talk Groups are like different work groups that you communicate with. They are programmed as “channels”. Several can share a Time Slot on a repeater like multiple PL codes can share a community repeater. Each talk group can be isolated from the other, but may get a busy tone if the same time slot is in use by another. Greater efficiency can be achieved by bridge routing and trunking techniques. Each radio can have more than one talk group and may scan or roam based on talk group.

Digital repeaters can be operated stand-alone but often they are linked to other repeaters using the same standard in a network. See the bottom of this DMR-MARC FAQ for a list of networks, of which DMR-MARC is one.

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Tags: section3.7

APRS (Automatic Packet Reporting system) is, according to the APRS website, “a two-way tactical real-time digital communications system between all assets in a network sharing information about everything going on in the local area.” it can transmit all types of data mentioned in the question.

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NTSC is the name of the standard used to encode colors in an analog fast scan color TV signal.

If you ask a broadcast engineer, NTSC stands for Never The Same Color, because his job is to keep all the cameras looking the same. Now that TV is in the Digital Age the only people you see using the NTSC broadcast standard are Amateur Radio Operators.

Actually, NTSC stands for National Television Systems Committee. They created the rules that governed what the broadcast signal would be electronically so every TV would be able to display the correct picture

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Tags: amateur television (atv) section3.7

It helps to know what APRS is and does. It transmits a station's GPS coordinates, so other stations can locate it. The components are a GPS receiver, a ham radio transmitter, and some logic to connect the two so the transmitter sends out the GPS coordinates. So:

It has nothing to do with counting packets, It doesn't require voice over Internet, and It doesn't count stations connected to a repeater.

It just provides real time communications that gives your location. In conjunction with a map, it shows your location to the stations that receive your GPS coordinates via the APRS system.

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Tags: aprs digital modes packet radio section3.7

Phase Shift Keying is a method for digitally transmitting data (with a computer of some sort) by varying (keying) the phase of the signal.

Phase refers to where you are in the cycle -- the peaks and valleys of the sine wave

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Tags: digital modes definitions section3.7

DMR (Digital Mobile Radio) is one of several digital modes. It's the only one that uses time-multiplexing to allow two digital voice signals to be repeated through the same repeater, using the same 12.5 kHz repeater channel.

It's not a position tracking system.

It's not a logging technique.

The third distractor is tempting, because it talks about two simultaneous repeater inputs, but the part about time-multiplexing is unique to DMR, so the best answer.

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Tags: digital modes section3.7

A checksum is an error detection method used by many data transmission types including packet radio. Basically all bytes in the message are added (summed) up and sent as a "checksum". The receiving station repeates this process and "checks" the result against the checksum it received from the sending station.

If the checksum fails (the sums don't match) then an automatic repeat request is sent.

Since packet radio is a form of amateur radio communications the destination station is generally identified at least by call sign, so that information is often included in the header as well.

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Tags: digital modes packet radio section3.7

CW stands for "Continuous Wave" which originally distinguished it from other types of emissions. (see Wikipedia for more information) At this point the origin of the name is less important than just knowing that it's a name for Morse Code, which is really just something you'll need to remember.

Take the 'W' in CW and flip it. Now it is an 'M'. Switch the C and M around. Now you have M.C. (morse code).

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Tags: section7.2

WSJT [Weak Signal JT(after the program's initial author, Joseph Hooton Taylor Jr.)] is software that facilitates short, quick digital transmissions and is very useful for weak signals.

As such, it's great for moonbounce (Earth-Moon-Earth), weak signal beacons and meteor scatter, all of which result in very little of the transmitted signal reaching anyone's receiver.

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Tags: digital modes section3.7

ARQ stands for Automatic Repeat reQuest

When the receiving station detects an error, it automatically sends a repeat request to the sending station.

It has nothing to do with encryption (which would be illegal except for sending commands to a satellite), or video signals, or data compression. Indeed, it takes a long time to have the receiving station send a repeat request and to then re-transmit the message, or portion of the message.

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Tags: digital modes section3.7

WiFi is the only protocol listed in this question that takes advantage of meshing. "Mesh Networking" is defined by Wikipedia as "a local network topology in which the infrastructure nodes connect directly, dynamically and non-hierarchically to as many other nodes as possible".

Repeaters may be networked but are often done hierarchically (e.g. a main node and child nodes). DMR is not mesh, and satellite communications are not as well.

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FT8 is a relatively new digital mode which became popular in 2017. FT8 stands for Franke-Taylor 8-Frequency-Shift Keying modulation. FT8 was created by Joe Taylor, K1JT, and Steve Franke, K9AN.

It very quickly largely replaced JT65 because it's much faster. FT8 is usually used on HF bands and it can achieve very long distances because it is extremely tolerant of noise and interference. It requires that both transmitter and receivers synchronize their computer time with the same time source (which is easy with the internet).

When you transmit, you transmit for 15 seconds and send only a very short (75 bit) message with a 12 bit checksum. Hint: Remember FT as fifteen.

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