GB7SD

Updated 2/7/2023 by Mike G0LQI

GB7SD

A DIGITAL VOICE REPEATER FOR SOUTH DORSET

GB7SD - PART OF THE SOUTH WEST CLUSTER

A 70cm repeater using DMR/TDMA technology - the new generation of Amateur Repeaters.

Tx: 439.4125 Rx: 430.4125

The current status of the South West Cluster can always be found here: www.facebook.com/groups/gb3bs/

DMR KEY FEATURES: Time Division Multiple Access (TDMA) preserves full channel width and divides it into alternating time slots that can each carry an individual QSO. The two-slot 12.5 kHz TDMA-based systems (providing 6.25 kHz equivalency) is more efficient. This means that two separate conversations can be handled by the one repeater, on the same frequency but on a different "channel". TDMA technology for narrowband 12.5 KHz provides advantages of: feature flexibility, lower equipment costs, longer battery life, future-readiness and spectrum efficiency.

Since initial switch-on we have been using Colour Code 1 and Talk Group 1 on both Slots. This has now changed to TS1-TG9 for local repeater traffic and TS2-TG950 for access to the South West Cluster, which includes GB7BS, GB7AA, GB7JB, GB7SD and GB7DR. It is recommended that all users change to these settings as soon as possible.

A useful guide to the SW cluster:

Working The Cluster | gb7bs.com

Notes from Ed G3VPF on recent modifications to GB7SD (3 Oct 2022)

After a gap of several days, GB7SD has re-joined the South-West Cluster.

I went up to the site this afternoon (Monday 3rd October 2022) and made the necessary changes to the codeplug and, somewhat to my surprise, it came straight up on the new server and appeared on the dashboards as expected. The situation now is as follows:

Slot 2 is still the South-West cluster as before. The only noticeable difference is that you must wait a few seconds when transmitting before you speak. The new network seems to take that time to sort itself out as one station drops carrier and the next station starts transmitting. You can now connect on the internet to the server and look at two dashboards. One shows which repeaters are currently operational on the SWC, the other shows any users transmitting on the cluster. The dashboards are available at: www.gb7bs.com/gb7bs/swc-dashboards.html.

Slot 1 is now connected to freeDMR. If you access it as before it will still work as before and be available for local contacts. The only difference you will notice is that there is now a rather strange voice announcement identifying the repeater. FreeDMR includes a Dial On Demand (DOD) capability which allows the user to connect to other talk groups. Once I have instructions on how to use this I will circulate to the group. In the meantime, if you want to experiment then please do so, but remember to return the repeater to local operation when you finish.

The Bristol Group are still refining the server settings, so things may change over the next few days/weeks.

Some additional notes:

Look at the FreeDMR website for a list of talkgroups available

Please, always disconnect the repeater when you finish by connecting to talkgroup 4000

If you want to know if the repeater is already connected to a talkgroup connect to talkgroup 5000 and a voice will tell you the current status.

You may want to monitor a particular talkgroup for long periods, but remember other users may not. You are welcome to use the facility to talk to other talkgroups, but if you just want to listen to a particular talkgroup then please consider getting one of the hotspots that are available. Remember, repeaters are primarily intended for use by mobile and portable stations.

You can get to step 3 in the attached document on many rigs by pressing the '#' key.

We are all learning how to use this new capability, use it wisely and it can be a great enhancement to what we can do, but there is always a danger of misuse ruining the capability.

Ed G3VPF

Please watch this page for further updates.

Please see the NEWS page for the latest updates on GB7SD

DIAL ON DEMAND TG.pdf

The image above shows our proposed South West DMR Network.

Historical archive

This section is of historical interest only and many of the links will no longer work.

On October 29th 2014 Amateur Radio DMR reached an important milestone by adding its 10,000th user ID.

DMR is the fastest growing Amateur Digital Network in the UK.

See here for more information about DMR in the UK: www.dmruk.net

DIGITAL FUND The matter of funding the Digital Repeater Network was discussed at the 2013 SDRG AGM and it has now been decided that a 'Digital Fund' should be set up by the SDRG to enable supporters to contribute towards the cost of the digital repeater hardware. This will include the actual repeater transmitter/receiver and the aerial system and duplexer.

The fund will be administered by the SDRG Treasurer but kept separate in the accounts. Payment can be made in the usual way, either by using the PayPal option on this Website here or by sending a cheque made out to 'South Dorset Repeater Group 2000' to the Treasurer: Rob Mott, G0ECX, 2 Dennis Road, Weymouth, Dorset DT4 0NJ Please mark your payment 'digital fund'.

12/02/14 The fund is already growing and more information will be posted here as soon as possible. Thank you to everybody who has contributed so far.

13/02/14 Our Treasurer reports that to date, almost £450.00 has been donated. It is estimated that approximately £1500 will be needed to cover the capital cost of each DMR repeater installation.

10/05/14 A pair of dipoles have been purchased for use with GB7SD.

21/11/14 At the 2014 AGM the digital fund income at the end of September was reported as being £599.78.

HISTORY/TIMELINE

During the 2013 AGM of the South Dorset Repeater Group the members present accepted unanimously a proposal from the Committee to investigate the possibility of installing a Digital Voice Repeater at Eggerdon Hill. An application has been made via the RSGB for a UHF Repeater using DMR technology and can be seen here: www.ukrepeater.net/my_vetting.php?repeater=GB7SD The site and facilities have been offered free of charge and there has been no request for funding at this stage. The callsign requested is GB7SD and has been used before by the SDRG and was the callsign used by the Packet Radio Nodes that were for many years located at our Ridgeway site.

It must be emphasised that it is very early days and there is no certainty that the application will be successful. There is therefore no need to rush out and buy a DMR radio, although many of those that are currently available are fully programmable and dual mode DMR/FM and suitable for existing Amateur FM use as well as those using DMR.

Another DMR Repeater proposal has been made for the GB3JB site: http://gb7jb.blogspot.co.uk/

15/12/13 The application is now with OFCOM. The requested frequency is: Tx: 439.4125 Rx: 430.4125 but please note that this is subject to change during the vetting process.

24/12/13 Two more applications have been made for DMR Repeaters:

GB7BS http://www.ukrepeater.net/my_vetting.php?id=1148

GB7AA http://www.ukrepeater.net/my_vetting.php?id=1160

Both are located in the Bristol area.

01/12/14 This page now has its own URL: gb7sd.co.uk

12/01/14 Another application for a DMR Repeater covering the Poole/Bournemouth area has been made:

GB7DR http://www.ukrepeater.net/my_vetting.php?id=1179

21/01/14 GB7SD has been cleared to go! Much to everybody's surprise the NOV has been issued for GB7SD.

27/04/14 The proposed site for GB7SD on Eggerdon is no longer available. It is hoped to use our Ridgeway site instead - see the News page.

10/05/14 A request for a site change is currently being processed by RSGB/OFCOM

31/10/14 The NOV was issued today.

01/11/14 GB7SD was switched on today and is now fully operational.

10/12/14 The Ridgeway end of the microwave link to Dorchester has been installed and tested. Once the Dorchester end is installed GB7SD will be connected to the SW DMR Cluster.

16/12/14 Since initial switch-on we have been using Colour Code 1 and Talk Group 1 on both Slots. This is currently being changed to TS1-TG9 for local repeater traffic and TS2-TG950 for access to the South West Cluster, which includes GB7BS, GB7AA, GB7JB, GB7SD and GB7DR. It is recommended that all users change to these settings as soon as possible

Please see the NEWS page for all the latest information.

Geoff, G0EVW - November 2014

A typical DMR Radio - the Motorola DM1400

DMR RADIO

Digital mobile radio (DMR) is an open digital radio standard for professional mobile radio (PMR) users specified in the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1-4 and used in products sold in all regions of the world. The applicable ETSI emissions compliance standards are EN 300 113 and EN 300 390. The standard was first published in 2005 and has been widely adopted by radio manufacturers and users.

The DMR standard operates within the existing 12.5 kHz channel spacing used in land mobile frequency bands globally. Its primary goal is to specify a digital system with low complexity, low cost and interoperability across brands, so radio communications purchasers are not locked into a proprietary solution. DMR provides voice, data and other supplementary services. DMR is a two-slot, time division multiple access (TDMA) system offering voice, data and a range of other features and applications. The specification covers the RF frequency range 30 MHz to 1 GHz and uses 4 level FSK constant envelope modulation.

In 2005, a Memorandum of Understanding (MOU) was formed with potential DMR suppliers including Tait Communications, Fylde Micro, Selex, Motorola, Hytera, Vertex Standard, Kenwood and Icom to establish common standards and interoperability. While the DMR standard does not specify the vocoder, MOU members agreed to use the half rate DVSI Advanced Multi-Band Excitation (AMBE) vocoder to ensure interoperability.