By Dale L. Puckett, KØHYD
These are exciting times in amateur radio here in the Wichita area. The VHF DMR repeater is on the air from atop Wesley Medical Center. This new machine creates many new possibilities for local hams.
Wichita Amateur Radio Club repeater trustee John Lock, KFØM, gives you the technical details. His excellent article in the March edition of the Grounded Grid, and found here on this site, also shows you the proper way to use it. I’ve worked with the repeater and had a lot of fun during the past month. Last week I spoke with John and we came up with a list of topics designed to complement his article. We both thought a quick introduction to time slots would be an excellent starting point.
Time Slots
Consider this: time slots are all about spectrum efficiency. Let’s compare them to a typical analog signal.
An analog FM signal is often 25 kHz wide. A DMR signal is only 12.5 kHz wide. The use of Time Division Multiple Access (TDMA) doubles the efficiency again. It allows the transmission of two separate conversations on this single channel. DMR using TDMA is then four times as frequency efficient as analog.
TDMA delivers this efficiency by splitting the signal. Alternating 30 millisecond slices carry the two conversations. Time Slot 1 and Time Slot 2 are the names given to these two time slices. John’s article describes how time slots work on the new W0SOE DMR repeater.
Static vs. Dynamic Talk Groups
The next topic John and I thought pertinent was the concept of talk groups. Consider this analogy: Imagine the two time slots as the two halves of a duplex home. The two sides of the house are independent and they each contain different rooms. In our analogy, these rooms are the talk groups.
The duplex may have two types of rooms, bedrooms and living rooms, for example. Our DMR talk groups also have two types: some are static and others are dynamic.
When a repeater operator creates a static talk group in a time slot that talk group is always available. Dynamic talk groups come and go.
To switch your radio to a talk group you key the radio with a channel pointing to the desired talk group. When you do this the hotspot or repeater opens a route to that talk group. Note: You may only do this when the channel is clear and no one is talking.
When you switch to a talk group the hotspot or repeater will stay connected until you disconnect, or until the end of the time out period defined by the repeater operator.
When you finish your conversation in a talk group, disconnect. Both courtesy and protocol dictate this. You do this by connecting to Talk Group 4000.
Sending a transmission to Talk Group 4000 disconnects the talk group you were using. Note: Do not do this yet on the new W0SOE DMR repeater. This functionality is being tested by the SysOps.
Pause Between Transmissions
What is the most important thing you can do in the DMR world? Pause between transmissions! The fast pace you need during HF operation makes it a hard habit to develop. But you must. Leaving a short pause gives other hams a chance to link to a talk group or disconnect from one. The connect and disconnect operations all must take place when no one is talking.
Another interesting note about DMR operation. If your radio cannot reach a repeater it will stop sending. Most of the time it will also place a message on your radio screen letting you know why it stopped sending.
Kansas vs. KS-Link Talk Groups
Someone once said that the dumbest question is the one that is never asked. Bowing to this theory I had to ask. I couldn’t for the life of me figure out what the difference was between the Kansas and the KansasLink Talk Groups. As it turns out the “Kansas” Talk Group is Brandmeister Talk Group 3120. Most repeaters in Kansas provide it, often as a static talk group. It’s where you’ll be able to hold a conversation with other hams in Kansas.
KansasLink is completely different. It is a network of repeaters in Kansas using both DMR and System Fusion. The repeaters are linked on an independent, locally provided network. While they do provide links to wide area networks to allow the use of popular talk groups, the primary focus is to provide YSF and DMR users with a high quality mobile network within Kansas.
The KansasLink repeaters provide “Kansas” on Time Slot 2, Talk Group 3120. All repeaters in the KS-DMR network carry this talk group. However, it is not the same as the Brandmeister Talk Group 3120. It includes only the repeaters on the KS-DMR network. Connection to a selection of Brandmeister network talk groups must be made on Time Slot 1. Conversations between users on repeaters throughout the state stay within Kansas and are not bounced off master servers around the nation and the world.
If you are using a DMR radio you connect to the repeaters on KansasLink by connecting to Talk Group 31203. If you are using a YSF repeater you connect to YSFReflector US-KansasLink by using the WIRES-X mode on your radio. To do this you connect to WIRES-X room 21696. It is important to note that YSF users need to avoid the use of Voice Wide (VW). Rather, they must use the DN mode. If they use VW their voices will not pass through the Brandmeister bridge.
Final Tidbits
In closing I thought I would pass along information about a new DMR network in Kansas. For information browse to http://ks-dmr.net/. This network is a partnership between the KØUSY Group, KØPRO and NV80 / N7KLR.
There is a lot of information on the KS-DMR.Net website. It includes details about a new DMR repeater in El Dorado. By the way, I can work this repeater using an antenna on my tower from west of Goddard. You’ll find it on 444.9875 MHz. The transmit frequency is +5. The Color Code is 1.
To find information about any repeater in the Brandmeister network, including W0SOE, browse to https://brandmeister.network. Click on the Repeaters tab on the left and then do a search.
Questions? Please Ask! Let me know what you want to read about here: k0hyd@arrl.net.