The admit criterion specifies a criterion under which transmissions on a channel are allowed. These criteria can be defined for both, analog and DMR channels. Irrespective of the channel type, the admit criteria “always” and “channel free” can be selected. The former simply always allows to transmit. The former requires the channel to be free.

For analog channels, usually there is also the criterion “tone”. This criterion would only allow transmissions if the matching CTCSS tone or DCS code has been received. For analog repeater operation, the criterion “channel free” should not be used as this would prevent any transmissions while the repeater is active.

For digital channels, usually there is also the criterion “color code”. This criterion would only allow transmissions if the matching color code has been received. To this end, this criterion is similar to the “tone” criterion for analog channels.

An all-call is a special type of an DMR call to a special number (16777215). All radios are supposed to receive this call irrespective of their particular configuration. This call type is usually used in emergency situations or on simplex channels.

Unfortunately, the local talk group (number 9) is frequently used on simplex channel although only those radios will receive calls to this talk group if it is in the group list assigned to the simplex channel. To be on the safe side, use the all-call for simplex calls.

The Automatic Packet Reporting System is a protocol that uses single broadcast frequencies to transmit small amounts of information though a network of repeaters. Usually but not limited to position reports. This allows other services (e.g., aprs.fi to display that information on a map. The usual APRS frequencies are 144.390 MHz (North America), 144.800 MHz (Europe) and 145.175 MHz (Australia).

The term “codeplug” is rather loosely defined. Usually it refers to the binary representation of the configuration of a radio that is written to the radio to configure it. It contains all contacts, channels, zones, settings, etc that form the configuration of the radio.

A color code is some additional information attached to each DMR call. It is used to prevent interference between repeaters with overlapping ranges that operate at the same frequencies. In amateur radio, this may only happen in very densely populated areas. It is much more frequent in commercial applications, where a single company may got only a few frequencies assigned but needs much more repeaters to cover a campus reliably.

The color code is a number between 0 and 16. A radio or repeater may only react to calls with matching color codes. Hence beside the actual input and output frequencies, the color code of a repeater must be known to be able to access it.

Means to control the squelch of a radio or to open a repeater, that does not rely on the strength of a carrier. Instead a tone is transmitted along with the audio, which is usually filtered out (e.g., less than 300Hz) by the receiver. There are a set of common CTCSS tone frequencies, but may radios allow for specifying arbitrary sub-tone frequencies.

DAPNET, short for Decentralized Amateur Paging Network does exactly what it says. It is a network of transmitters that transmit pager messages in the UHF band, usually at 439.9875 MHz. As the old pager operated at a frequency near by, they can be modified to operate at that frequency and can therefore be used in amateur radio.

The DAPNET is particularly popular with emergency operators as it allows for an convenient and reliable multicast notification.

Stands for dual capacity direct mode. This allows for two independent connections on a single simplex channel by TDMA. Lacking a single central repeater, one of the participants must act as the so-called leader. This radio then defines the clock and thus time slot 1 and 2. All remaining participants must act as so-called follower. They must synchronize to the clock of the leader. This obviously requires that all participants can reach the leader directly.

Similar to the CTCSS tones, the DCM allows to open the squelch or repeater by transmitting sub-tones along with the audio. These tones are usually filtered out by the receiver (e.g., below 300Hz). In contrast to CTCSS tones, DCS uses these tones to repeatedly transmit a digital code.

EchoLink is a network of analog FM repeaters that allows to link repeaters within this network temporarily. That is, two FM repeaters that are linked via EchoLink behave like a single repeater irrespective of their location. This network also allows to access the repeaters directly though the internet. This is particularly helpful if one cannot reach any repeater.

A group call is simply a call to a talk group. That is, not to a single participant but rather to a group of participants. Every participant that has this talk group in their group list can receive this call. See also Group List and Talk Group.

A group list is a simple list of talk groups. A group list is then assigned to a channel to specify which group calls to receive on that channel. If a talk group is not listed in the group list of a channel, the radio will ignore calls to this talk group on that channel.

The DMR network cannot know which talk groups you are interested in. You have to tell your radio using group lists.

The hang time specifies the time period, a DMR call remains “active” after it ended. For this time period, the call will replace the default transmit contact on that channel. This allows to directly answer a call received on a channel, even if that call is not the default transmit contact on the channel.

The Maidenhead locator, also known as “QTH locator” or “IARU locator” is a means for transferring a geo-location over radio. Using a so-called grid-square system.

“Lone worker” refers to a feature of many DMR radios used in some commercial settings, where a participant in the network needs to report regularly to some other station. This feature is certainly not very useful for the HAM radio context.

A DMR call to an individual participant. Usually, radios do not receive private calls not addressed to the radio. This therefore can be used to talk to a specific HAM over a repeater without disturbing other participants. The repeater however, will be blocked during that time.

A revert channel is a designated channel the radio resorts to, to transfer some information or the radio switches to, when the PTT is pressed. This is usually used in the context of APRS (i.e., the channel to switch to send the position) or scan lists (i.e., the channel the radio will switch to, when the PTT is pressed during the scan).

Specifies which settings of the current channel needs to be overridden to stay in contact with a particular talk group. These settings are usually those, specific for a repeater. That is, receive and transmit frequency and color code. The time-slot might also be overridden.

A collection of roaming channels usually sharing the same transmit contact. When roaming is enabled (and supported by the radio) this list of channels is scanned for a reachable channel once the current repeater gets out-of-range. This way, one can stay in contact with a particular talk group when being mobile.

AX.25 addresses (and thus APRS) consists of a call sign and a so-called SSID (0-15). This number can be used as a replacement for the lack of ports in AX.25 or to provide some additional information about the station.

The term “Talk Group” refers to a DMR ID, which represents a virtual contact. DMR repeater may subscribe to one or more talk groups. Every call to these talk groups are then transmitted by those repeaters, that are subscribed to these talk groups. Usually, it is possible to subscribe a repeater to any talk group temporarily by simply starting a transmission to this talk group on a repeater channel. For some time period after the initial transmission, the repeater will transmit all calls to this now subscribed talk group. The subscription gets renewed with every further call the talk group.

See Also Group Call.

Due to the lossy compression of audio data, it is possible to send more than twice the amount of audio data through a single 12.5kHz wide channel than needed. This allows to provide two independent audio streams within a single physical channel.

There are basically two ways to separate these two audio streams. Either by frequency, effectively splitting the single 12.5kHz channel into two 6.25kHz wide ones. Alternatively, one can split the channel in “time”. That is, the band width remains 12.5kHz but each of the two simultaneous participants sends one after the other. One in time slot 1 and the other in time slot 2. This is called TDMA and DMR uses this technique to provide two independent audio and data streams within a single physical channel.

For this TDMA to work, one participant needs to define the “clock” to specify when time slot 1 or 2 happen. This role is usually taken by the repeater but on direct simplex connections, one of the participants might provide that clock. This is then called DCDM (Dual-Capacity Direct Mode). This mode, however, makes little sense in amateur radio context.

A transmit or default contact can be specified for each DMR channel. Some radios actually require that each channel has an transmit contact. This contact can be any contact you want to call whenever the PTT is pressed on that channel.

It is, however, possible to answer any received call directly by pressing the PTT button within the so-called hang time, although the call may not match the transmit contact. These hang times can be set within the radio settings, usually for private and group calls separately.

It is also possible to call any contact by selecting it from the contact list or by entering the contacts DMR ID into the keypad.

Specifies the time of continuous transmission, after which the transmission is interrupted automatically. This prevents the accidental blocking of a repeater or talk group by transmitting continuously.

A scan list is just a list of analog and digital channels that one wants to scan. A scan list can be associated with each channel. This scan list is then used whenever a scan is started on that channel.

As there are usually several channels defined per repeater (at least two), the number of defined channels grows rapidly. To organize this large number of channels, zones are used. These zones usually collect all relevant channels for a region. That is all (analog and digital) channels associated with the local repeaters. The relevant zone is then selected via the keypad on the radio and only those channels in that zone are then accessible.

Some radios allow to specify a different zones for each VFO. Others set a zone globally. In the latter case, the zone consists of two channel lists. One for each VFO.