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REAST Presentation - Digital Voice Hotspots



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Presented by Scott VK7HSE.

Apologies about the first 4 minutes of audio not being available - in this time Justin VK7TW introduced Scott and Scott went through the Zumspot, OpenSpot1, Openspot3 and Pi-Star hotspots that he brought along on the night. Scott then started to show the Pi-Star web based dashboard.

00:04:15 - Audio starts - There was a description of the hotspots and whether they support DMR, D-STAR, YSF/C4FM/Fusion, P25, NXDN and Tetra and the Openspot3 is the set and forget option for amateurs although they are relatively expensive.

00:13:20 - There are simplex hotspot and a duplex hotspots. Simplex hotspots can only receive and transmit one timeslot or mode at a one time.
DMR Hotspot Dashboard - https://vkdmr.com/hotspots/

00:16:50 - Description of the VK DMR network with the Pi-Star Dashboard showing a D-STAR broadcast at the same time. Scott described the fact there is s 3minute time out timer on most digital voice repeaters and therefore there are systems to drop the carrier every 3 minutes to reset the timeout timer. Usually done with an Arduino switching the PTT line.
VK DMR website - https://vkdmr.com/

00:19:50 - Scott described the dynamic setup of a hotspot where you can key up the talk group you want versus a statically configured hotspot where you can configure many talk groups.

00:22:00 - The hotspot frequencies in VK are 439.150 and 439.125MHz. The software on the hotspot can lock to your callsign only. The convention is that hotspots are a single user device. Hotspots are usually pretty deaf to reduce multiple users. Never put an amplifier on a duplex hotspot as there are many spectral artefacts.

00:26:30 - The hotspot status webpage for VK was displayed and Scott went through the VK7 showing on the dashboard and what things meant on the dashboard.

00:29:00 - Scott threw it open to questions. First question was about MMDVM limitation of hotspots monitoring five talk groups per timeslots. Scott described the scenario where monitoring too many static talkgroups can lock up the hotspot and also flip to conversations on other talkgroups and you can miss the conversation you were on without some manual intervention. This is to do with the hangtime on each talkgroup.

00:35:00 - using the System Cron to setup the Pi-Star hotspot to switch to particular talkgroups. There are many advanced feature on the Pi-Star.

00:37:00 - The Australia-wide talkgroups are shown on the VK DMR website: https://vkdmr.com/using-dmr/
Talk Group 8 is setup to only activate VK7RAD, VK7RCR and VK7RJG on timeslot 1.

00:41:00 - Tetra description with 4 timeslots in trunking mode across about 150kHz bandwidth channel like a cellular phone network in a UHF spectrum.

00:43:20 - Setting up your handheld for a hotspot - modifying a code plug. Scott then went into the jargon or lingo associated with DMR and the sequence to setup the configuration for hotspot operation. It the Zone, Talk Group, Channel and Contacts. The IOpenGD77 project simplifies the configuration and you only need to setup the contact, channel and the zone.

00:49:25 - The codeplugs on the REAST website are slightly out of date and will be updated when time permits.

00:51:00 - Outline of the OpenGD77 project issues and how this was overcome by uploading the original firmware then overload the updated firmware to overcome the licencing issues.

00:54:00 - Code plugs discussion and the feeling is that you stick with specific simplified structure that meets the local need.

00:55:40 - Each DMR network - VKDMR 3801-3808 = BandMeister 5051-5058 these are linked between the DMR networks.

00:58:00 - Demonstration of the timeout periods on each channel on the DMR hotspot dashboard. Scott discussed the differences between a hotspot and repeater and the differences between the Yaesu DR-1X and DR-2X repeaters.

01:02:00 - Distance limitation of DMR is 32km which is limited by TDMA timings. D-STAR not being a TDMA mode the distance issue does not exist. If you have a multi-pathing DMR radios will most likely not work.

01:06:00 - Scott outlined his opinion of recovered audio quality is P25, NXDN, C4FM, DMR then D-STAR.

01:09:30 - The DRM specification came from Europe to improve spectral efficiency as there are two timeslots/channels on the one frequency, this is same with P25 which is another TDMA mode.

01:11:30 - A discussion on sending text messages over the DMR / DV network which is possible if the repeaters are configured to support. On the amateur networks most configurations drop any packets other than the digital voice packets so texting may not be available.

01:16:10 - Scott announced that VK7RAD has just been put on the VK YSF/C4FM network courtesy of Peter Brennan and Scott's work.

A huge thank you to Scott for this presentation.
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Audio
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