A DIGITAL VOICE REPEATER FOR SOUTH DORSET
A 70cm repeater using DMR/TDMA technology - the new generation of Amateur Repeaters.
Tx: 439.4125 Rx: 430.4125
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:
lower equipment costs,
longer battery life,
GB7SD is not currently connected to the South West Cluster.
There is no Internet connection available a the moment.
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.
Please watch this page for further updates.
Above update kindly provided by Dave, G3ZXX
Please see the NEWS page for the latest updates on GB7SD
The image above shows our proposed South West DMR Network.
(Click on the image to enlarge it)
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.
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:
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:
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
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.
MORE INFORMATION AND LINKS
There was a very interesting article in the the November 2013 edition of RadCom about the first UK DMR Repeater, GB7TD in Yorkshire.
The full specification and capabilities of DMR can be found here: http://dmrassociation.org/the-dmr-standard/
Some Amateur DMR Repeaters are linked via a world-wide Network known as DMR-MARC. See here: www.dmr-marc.net
See here for more information about DMR in the UK: www.dmruk.net
SDRG Information >