Working The Cluster

All content is Copyright of The Bristol 70cms Repeater Group

Working The Cluster Network.

The Repeaters.

Each of the five repeaters, GB7AA, GB7BS, GB7JB, GB7SD and GB7DR all operate on different RF channels.

Each repeater has two Time Slots available to it which can carry separate voice QSO’s on each of the slots. Or in other words, two different and separate QSO’s on the single RF channel, at the same time.

Each repeater will transmit at 100% duty cycle RF power irrespective if only one Time Slot is in use.

Each Time Slot equates to just 6.25KHz of RF bandwidth.

Each repeater is capable of relaying both Voice Data, Private Call voice Data, Text Messages and supplementary data services.


The repeaters will closedown after 7 seconds if there is no activity on both Time Slots.

Repeater Time Out is set for 4 min.

Talk Groups.

Talk Groups are probably the most important item in DMR to become familiar with.

A Talk Group is basically exactly what it says; it is a place where Groups of users all Talk together in one place. A Talk Group is given a unique number and can range from 1 to in excess of 16700000.

The world wide DMR Network uses many Talk Groups for different things and a list of them can be found on the web. For example one Talk Group maybe set up for World Wide English speaking users. While another could be for users using a different spoken language or a Talk Group for Local QSO’s only.

While having many Talk Groups available is all very well, but with a Repeater only having two Time Slots available this raises a problem. How do you fit all these Talk Groups into two Time Slots at the same time? The answer is you can’t!

If both Time Slots on a repeater are in use serving two different Talk Groups and suddenly someone on a completely different Talk Group wants to put a call out then the system will block his call and the person/radio attempting this call will get a Busy indication. A bit like an engaged tone on your telephone, the line is already being used!

From long term monitoring of this arrangement on the world wide DMR-Marc Network we found that this arrangement causes much confusion and frustration for people. It is mainly for this reason that we decided not to become part of the DMR-Marc Network as it currently is. Other people may have a different view regarding all of this but it is something that the keepers and users of the South West Cluster Network agree upon.

The repeaters that form the South West Cluster only use two Talk Groups. They are Talk Group 9 for only local repeater QSO’s. And Talk Group 950 for QSO’s that will be broadcast over all of the Clusters Networked repeaters, at the same time.

With this arrangement there is no problem with congestion, in having more Talk Groups than Time Slots. This also cuts down on confusion as to which Talk Group to use. Simply put, two Time Slots, Two Talk Groups, which are available 100% of the time.

Talk Group 9 was selected because it is also used in the DMR-Marc Network. This allows users from outside the area but who are familiar with the world wide DMR-Marc Network to also use the South West Cluster Network without the need to program a special or different Talk Group into radio’s. It also supports the reverse, a user who uses the Cluster can also use the same Talk Group on any repeater connected to the DMR-Marc Network.

The only difference is Talk Group 950, which has been registered and issued specifically for the South West Cluster Network and is already being adopted and recognised by the world wide network.

Do please ensure you only use:

A registered DMR-Marc ID.

Talk Group 9 on Time Slot 1 for Local Repeater QSO's.

Talk Group 950 on Time Slot 2 for QSO's across the Cluster Network.

If the above is not adhered to, then you may not be heard at all.

Equipment Programming.

DMR technology comes with a new set of rules. Remember, DMR was initially designed for commercial use, and has been adapted in ways for it to be used in the Amateur world.

For the system to work and provide all the facilities it was designed to do relies on the users radio (the Terminal) to be properly programmed. If not then this can cause interference problems with not only your equipment, in the way it operates, but to the network and users as a whole.

On this site we have a good FAQ section which should help most people to get started with DMR. However there are many settings to get right with a Terminals programming. Most of these are covered in the FAQ section but the most important ones are listed below along with the correct setting.

But firstly, if you have not done so already, PLEASE obtain a valid DMR-Marc user ID.

A valid user ID is important as it ensures that there are no duplicated ID's operating on the SW Cluster Network or on the DMR-Marc Network, if you intend to use it. This ID number is unique to you and your callsign.

PLEASE do not just make up or use your own ID on the repeaters as it will cause problems for you and other users.

You can get a valid user ID here: (up to 3 ID's per callsign).

Colour Code – 3 for GB7BS (Repeater specific).

Rx Group List: Talk Group 9 or Talk Group 950 depending on Time Slot.

Tx Contact Name:  Talk Group 9 or Talk Group 950 depending on Time Slot.

Time Slot 1 to only allow Talk Group 9.

Time Slot 2 to only allow Talk Group 950 (The Cluster).

Transmit Admit Criteria – Set to “Colour Code Free”.

In Call Criteria – Set to “Follow Admit Criteria”.

Digital Mic AGC – Turned off.

Talk Around – MUST be Disabled or turned off for any Repeater channel.

All settings regarding Emergency Calls or Man Down MUST be disabled.

Message Delay set to 90ms.

PTT Timer set to 4min.

RSSI Roaming Threshold set for -108dbm (suggested setting if Roaming is used).

Below is a list of all the Repeaters linked into the South West Cluster Network.

Repeater Channel List

Repeater & Channel list produced by Dave G3ZXX.