ANALOGUE VS DMR

There are several differences between analogue and DMR, the main ones that affect users are the terminology, operating procedure and programming of the radio. Others include bandwidth and signal degradation.

OUT OF THE BOX EXPERIENCE

With most analogue (FM) radio’s they are ready to go straight out of the box. DMR on the other-hand often isn’t quite so user friendly, requiring some research and understanding of the mode.

You may be lucky and purchase a DMR radio that’s already been pre-programmed, but that’s as near as you’re likely to get if you’re looking for a ‘plug’n play’ offering.

Most seasoned users will have been through the ‘how do I do this’ or similar phase, but the newcomer to the mode still has learn their way around what DMR can or can’t do.

It’s all about managing expectations and hopefully that’s where this guide and other similar information will help. DMR, whilst being technically different from other modes, is no less enjoyable once you take the time to read about and understand the differences between analogue & DMR.

BANDWIDTH

An analogue repeater allows a single voice transmission through 12.5kHz of bandwidth where as a DMR repeater allows two simultaneous transmissions through the same bandwidth by use of two time slots.

TDMA (time division multiple access) sends the transmissions in alternating 30 millisecond slots which are syncronised by the repeater.

SIGNAL DEGRADATION

To all intents & purposes, signal degradation between analogue (FM) & DMR is negligible and comes down mainly to perception.

Irrespective of the mode of transmission, the RF will travel for roughly the same distance for both analogue and digital. The signal will weaken the greater that distance becomes and whilst our ears play a large part in ‘decoding’ the audio on an analogue signal, the electronic ‘ear’ used in digital modes, is far better at decoding the audio under weak signal conditions.

Hence the perception that digital travels further than its analogue counterpart.

As can be seen from the diagram below, the audio quality is better maintained for digital under poor signal conditions than for analogue. As previously mentioned, this is largely down to the technology rather than any other factor.

TERMINOLOGY

This is covered under the “terminology” menu – https://www.dmrguide.uk/index.php/terminology/

PROGRAMMING

This is covered inder the “Programming Basics” menu – https://www.dmrguide.uk/index.php/programming-basics/

OPERATING PROCEDURES – 1

PAUSES

This may seem like a simple topic but with the advent of digital transmission and network-linked repeaters in particular, as responsible radio operators we need to redefine our approach to the humble ‘pause between overs’ that we’ve become used to in the analogue world.

Standard Pause:

With analogue transmissions, either simplex or via a repeater, it’s been the adopted procedure to leave a short pause between overs (usually about 1-2 seconds) as a courtesy to other users who may wish to join the conversation or call another station. For the purpose of this guide, we’ve called it a ‘Standard Pause’.

Longer Pauses – why they are needed:

Whilst digital transmission & network linked repeaters offer us a wider and more varied range of networks and users, it’s not without its problems and limitations. One of those is Network Latency or delay.

Whereas analogue transmissions are almost instantaneous user to user, digital transmissions have an inherent processing delay as they travel through the network, which can sometimes be as much as 3-4 seconds in the worst cases. A good working example is if you have access to more than one repeater in your area. If you listen to the same Talkgroup on both repeaters, it’s unlikely that the two audio streams will be synchronised.

There are times when this delay is quite considerable, meaning that the person you’re listening to could well have actually stopped speaking by the time you hear them finish their over. It may only be 2 seconds, but it’s enough to cause potential problems for other users on the network.

It is therefore suggested that a longer pause of perhaps 4-5 seconds is allowed between the end of one over and the start of another. This should not only give enough time for the networks to ‘catch up’ as it were, but also provide some leeway for other users to break in, either to join your conversation, but perhaps more importantly, to switch between Talkgroups on the same Timeslot.

With the advent of cross-network access, the importance of leaving longer pauses has become more relevant due to the complexity of how the networks are linked and the inter-network delays. Occasionally a cross-network transmission has not to been relayed due to the network itself not having time to ‘reset’ – i.e doesn’t see the end of a valid transmission.

In Summary:

When using digital networks (of whatever flavour), it is recommended that the ‘pause between overs’ should be around 3-5 seconds. If you’re in QSO and are requested to leave a longer pause, please do so in a courteous manner. Leaving a long pause will not mean that you loose your slot to another Talkgroup – that’s why the hold-off timers were introduced.

OPERATING PROCEDURES – 2

The operating procedure depends on the network you are using. Some networks may have their own guidelines on their websites which are mainly in place to prevent unnecessary use of wider area talk group when another suitable talk group can be used, thus freeing up repeaters / time slots for other users and reducing data usage especially where there is a mobile internet connection.

Phoenix has a mix of “calling” and “user activated” channels where the calling channels cover a wide area. TG1 (Worldwide), TG2 (Europe), TG13 (English WW) and TG235 (UK Wide) are seen as the calling channels. These are supplemented by TG119/TG129 (Worldwide UA), TG113/TG123 (English WW UA) and TG’s 80-84 (UK Wide UA). Whilst short QSO’s are generally acceptable on the wide area groups, longer QSO’s should move to a UA group in order to allow others the opportunity to put out a call since these talk groups are all on the same time slot. More info here – http://www.dmr-uk.net/index.php/layout/

The Northern DMR Cluster follows a similar policy to that of Phoenix as it utilises the same talk group structure and they also have a blacklist policy which can be read here – https://www.northerndmrcluster.com/policy.html

Brandmeister has a different route as most of the +1400 talk groups are user activated. The repeater keepers decide which talk groups will be “always on” and some also have TG91 (Worldwide) as “always on” using a schedule so it’s only on during the Saturday net. TG9 TS2 is usually linked to reflector 4400 (UK Wide) for which they have an “acceptable used” policy (http://www.bm-dmr.uk/dash/4400%20use.html) where it can be used for short QSO’s and users are to leave gaps for others to join or put out a call. Also, as the network has numerous talk groups covering many countries down to smaller states, counties and regions, please take in to consideration the the area that the talk group you are using will cover.

Clusters (SALOP & SW Cluster) do not seem to have any published guidelines or policies however it would be ideal not to use the cluster TG (TG75 on SALOP and TG950 on the SW Cluster) for chatting to someone on the same repeater.

OTHER

There are a few other differences due to DMR being internet connected such as having live monitors and the ability to send text (sms) messages to other users on the network. DMR can also be seen as an alternative to HF in regards to making long distance contacts, through internet linking of repeaters and hotspots. Hotspots have also progressed a lot to the point where users can take them mobile/portable to maintain contact when there are no repeaters in range (subject to having mobile signal).

There are pros and cons to all systems and we should not see any as being superior to another. As amateurs like to experiment, so we will do so with various modes just as we have done with D-Star, Echolink, IRLP and now moving onto NXDN, P25 and Tetra.

Facilities such as Hubnet (https://www.hubnetwork.uk/index.php) allow many modes to link together – Allstar, Echolink, Analogue FM, DMR (Phoenix, Brandmeister & TGIF), WiresX and D-Star. Many digital modes include bridges to different systems so that we are not fully segregated.