Talkgroups vs reflectors

I’ve been thinking recently about talkgroups and reflectors.

In the beginning, I saw that the UK had chosen reflectors, so I went about trying to build a repeater that only used one talkgroup (TG9 on both slots). I experimented with TalkGroup rewrite to allow access to other talkgroups but still rewrite them to TG9 at the repeater. This was interesting and educational, but it was not perfect.

Later, for technical reasons, the code I had contributed to the MMDVM project to make this happen had to be removed.

Recently, I’ve been pondering this “sitting on the fence” approach of having reflectors and talk-groups. To be honest I think it’s messy to use both and perhaps we should choose one or the other, or at recognise that they have different purposes. In particular, it makes things harder for mobile users as manual-dialing reflectors can be to taxing whilst driving. Also, many radios don’t actually support this functionality, e.g. my MD650 I use in the car does not.

So what do you, as users, think. Should we remove the default connection to 4400 on TG9? Reflectors would still be available on demand but would disconnect after 10 mins or so of inactivity.

This does not mean we have to give up 4400. 4400 is also TG2350 so in place of an always-connected reflector 4400, I can make TG2350 static. This gives an option to use roaming on this TG too.

Note, we are the only country in the world that has this obsession with reflectors. Everywhere else the primary access method is talk-groups, with reflectors available to connect when required. This is sensible because regularly used talk-groups are always there, but if you want to try something new, just connect it as a reflector and try it out.




GB7FR Intermittent TX fault

FR has an intermittent TX fault. Thankfully its not causing too much problem today. I am looking in to it. When the fault occurs, the TX radio puts out blank carrier. Work continues….


It seems there is still a problem. I am going to look into replacing the TX radio, then I can take my time over repairing (if possible) the current one.

Talk Group Rewrite disabled.

I have today disabled rewrite on FR because some changes made to support more advanced DMR features (embedded GPS etc) are incompatible with it and I want FR to be fully functional in this respect.

Everything else is as normal.

Please note also, TG23150 (aka reflector 4411) is enabled as a static TG, as a trial, on TS1. This is the South East group and if also enabled on other South East repeaters, will allow true roaming between repeaters in the group.

The link to BH on TG9 TS1 also still exists and can be used for the same purpose between these two boxes.

GB7PK was removed from BrandMeister so we no longer have a link to PK.

Twitter Feed

Something I forgot to mention in my last post:

As well as SMS, the repeater now publishes it’s RF heard contacts via Twitter as the ID @GB7FRfeed. Also, when the system is finished, you will be able to add friends you want to watch and it will notify you via a mention in a twitter post, via email or DMR sms.

November update

I’ve been hard at work behind the scenes recently. Enhancements include:

  • Repeater dashboard (see sidebar link)
  • Talkgroup ReWrite (see user guide)
  • Slot 1 also supporting TG23510, rewritten to TG9 (see user guide)
  • Purchased some RG214 to upgrade the radio <-> duplexer links, to minimise possible de-sense from stray RF.
  • SMS service – repeater is able to send welcome messages, send you your current BER etc. (More on this soon, in the mean time, please see user guide).

I am also interested in getting some feedback on some points of discussion:

  1. Should FR go true multi-mode? Note, I don’t have radios for other modes at present, so this would require input from other stations to monitor the repeater in other modes, either by loan equipment or by users listening and reporting back to me if any issues are seen.
  2. GB7FR social meet – I’ve been meaning to do this for ages, probably at The Henty in Ferring. Are you interested?

Feedback welcome.


73 Simon


During JOTA this weekend, FR will default to the JOTA reflector on TS2 TG9. Please support the Scouts and make some contacts.

Of course, you are free to move the repeater to another reflector if you wish.

Connect talkgroup by private call

I have today implemented a feature whereby you can connect a talkgroup to TG 9 on slot 2 using the same mechanism as a reflector. So, for example, you can place a private call to ID 1 and TG1 will be connected to TG9 until it times out. If you want to reply on TG1, you must respond within the callhang (carrier) period on the repeater, or place a new private call to reconnect.

New feature – TG Rewrite

I have today enabled a new feature on FR – TG Rewrite. I coded this for MMDVM to try and provide talk-group access whilst avoiding the slot-contention problem. It is currently enabled on slot 2.

Details below – from the readme file:

Talk-Group Rewrite was conceived as a way of making talk-groups behave more
like the reflector system and of attempting to solve the problem of “slot
contention”,where the user may be locked out of a slot by traffic on a
talk-group they know nothing about, without knowing why. This is frustrating to
users, both those new to DMR and seasoned DMR users.

TG Rewrite, when enabled for a slot, rewrites the DST ID of incoming talkgroup
traffic to TG9, alowing audio to be heard by any user monitoring TG9 on that
slot. If the user then replies on TG9, as long as they key-up during the
CallHang period, the DST ID (TG) is again rewritten on the outbound traffic,
which transparently maps back to the originating talkgroup.

To use a User Activated talk-group, briefly key-up on that talk-group to
activate it, then switch back to TG9 and talk as normal. If the CallHang period
expires, you may need to activate the talk-group again by keying up on that
talkgroup briefly, as before.

It is useful to set the CallHang parameter to a generous amount. I am currently
using seven seconds.

Two boolean configuration options control the TG Rewrite feature:


ACL’s are applied before the rewrite, so still apply to rewritten traffic on source talk-group.