Digital Channel - Options with Vague Descriptions

[W4JEW]

Hello,

As I spend more time in the OpenGD77 CPS software, I find options that have supporting in-line help, but still do not provide enough information.

When looking at the various options available when configuring a channel, there are four check boxes on the lower right-hand corner of the dialog box:

1. Private Call Confirmed

In-Line Help:

This feature sets Private Individual calls on the current digital channel as confirmed. By default, Private Individual calls are unconfirmed. If enabled only rx, this feature will be disabled.

It would be helpful to understand what the difference in behavior is between a private call when it's unconfirmed vs. confirmed.

When would someone use this?

2. Data Call Confirmed

In-Line Help:

This feature enables individual packets in data calls on the current digital channel or personality to be confirmed (i.e. acknowledged) on the current digital channel to be confirmed on the Data Link level. The transmitting radio resends data packets in the data call if the receiving radio does not respond with Data Link level acknowledgements or confirmations upon receiving the data packets. By default, data calls are unconfirmed. This is a channel-wide feature.

When would someone use this?

This one will probably make more sense once someone explains the difference between confirmed and unconfirmed for Private Call Confirmed.

3. Emergency Alarm Ack

This feature identifies a single packet in the current emergency call on the digital channel, or is used to confirm (respond to) the personality on the current digital channel on the data link layer. If the receiving interphone receives the packet without giving any confirmation information or response information to the data connection layer, the transmission interphone sends the data packet again in the data call. By default, the data call is in an unacknowledged state.

What in the world is an "interphone"?

I'm fairly certain anything related to Emergency Systems/Alarms are only used in non-ham radio related use cases, but there may be people using Emergency Systems for other reasons. If so, please provide some background on how you might use this.

4. Dual Capacity Direct Mode

In-Line Help:

The Dual Capacity Direct Mode (DCDM) feature supports two simultaneous subscriber transmissions within a 12.5 kHz channel bandwidth for Direct Mode transmissions. The radios within the same group must use the same timeslot so that the group using timeslot 1 does not interfere with the group using timeslot 2. For proper operation, the radios need to identify and track the timeslot structure. A unique radio is elected as a channel timing leader. The other radios adjust their clocks to synchronize as possible with the channel timing leader.

What does this do (in plain English)?

When would someone use this?

Thanks in advance!

73,

-JeffH

Jeff Hochberg
W4JEW
Atlanta, GA

[kd2lh]

This will get you started.

The details are in the ETSI specification for DMR. The DMR standards are all at: https://www.dmrassociation.org/dmr-standards.html


This is a writeup from a commercial manual that discusses the feature:

Private Call Confirmed

This option configures whether the radio sends a confirmed private call request when user is trying to initiate a private call.

Checked: The radio sends confirmed private call request upon private call initiation.

Unchecked: The radio sends unconfirmed private call request upon private call initiation.

Default: Unchecked
Note
The RX Only option must be unchecked. This feature is available for digital channel only

In this mode, when a radio initiates a call, it can start with a digital handshake that must be digitally acknowledged before the radio will proceed with the contact. The feature makes sure that the radio you're trying to contact by private RadioID is on the channel before proceeding.

If you have two radios, you can try the feature out. In many commercial setups, there are a number of radios active, with a group call typically used to speak to everyone on the channel. If a single radio user wants to contact another user directly on the same channel (without others involved) private call can be used. The confirmed feature makes sure that they are on the channel before proceeding, and makes sure that another conversation isn't active simultaneously (either group or different private ID).

[kd2lh]

DCDM (Dual Channel Direct Mode) is an interesting adaptation that allows two independent conversations on one channel to take place directly between radios without a repeater involved.

https://cwh050.blogspot.com/2012/12/dcdm.html

It works by adding control and timing signals so that all the radios on a simplex channel can properly sort out the two time-slots that are used.

When you use a repeater, it makes use of two 12.5khz radio channels, and the repeater manages the clock timing and phase involved in forming and separating the two time slots. In effect the repeater has the master clock used by all radios to form and separate the time slots.

DCDM lets radios communicate directly and simultaneously on both time slots on one channel. One radio ends up being the master clock, and the others adapt to it. If I remember correctly, DCDM adds additional timing and handshake signals to connections.

[G4EML]

Also be aware that none of the the options you have listed are implemented in the OpenGD77 firmware (and may never be).

The CPS is a modified version of the one used by the original firmware. As such it still contains many options that are not supported by OpenGD77.

Development effort is concentrated on those features that are of the most use for amateur radio.

Colin G4EML