How To Program Your DMR Radio For The Balloon Single Frequency Repeater

One of the recurring payloads on the Richardson-area balloon flights is a DMR single-frequency repeater (SFR). This payload is very effective as a voice repeater, and very simple to access if you have a DMR radio. In various forms, we have been flying DMR repeaters for almost 10 years. Near apogee, the DMR repeater will cover most of Texas, Oklahoma, Louisiana and Arkansas, with some Kansas, Mississippi, and Missouri.

After our Balloon is in the air, the DMR Single-Frequency Repeater will be active. Since DMR has two timeslots (T1 and T2), some DMR radios can “listen” on one slot and “transmit” on the other at the same time. This allows you to transmit to the balloon and be received by all other DMR radios at the same time – just like a mini repeater in the sky. We want to know how far you can talk!

The purpose of this post is to help you program your DMR radio (or the one you intend to buy soon) so you can access the repeater payload on our weather balloon launch targeted for May 3rd. If you make a contact through the DMR repeater on the balloon, or interact with any other payloads, you’ll be eligible to receive a special event QSL card from the Richardson Wireless Klub.

How does the single-frequency repeater (SFR) work? When you transmit, the HT flying on the balloon will receive your voice packets and retransmit them in the opposing timeslot. This leverages the TDMA architecture of DMR — the 50% duty cycle means the repeater can retransmit your voice packet right after receiving it. Although the packets are retransmitted on the opposing timeslot, they are still encoded as if they were on timeslot 1.

What radio will be flying on the balloon payload string? A Hytera PD982 with the SFR license. This radio has flown several times with great success.

For the experienced DMR operator:

The payload will be on Simplex 1 (UHF) per the DMRTexas website — 441.0MHz / CC1 TS1 / TG99. If you have receive groups, make sure that TG99 is in your receive groups list.

For the DMR operator-in-training:

1. Add Talkgroup 99 as a Group Call to your talk group list (sometimes part of your “contact list” depending on CPS).

2. Create a channel for Simplex 1 with these settings:

— RX Frequency: 441.0
— TX Frequency: 441.0
— Channel Type: Digital
— TX Permit / Admit Criteria: Channel Free
— Contact: TG99 (per step 1)
— Color Code: 1
— Timeslot: 1

3. Add the Simplex 1 channel to a Zone.

4. Program to radio

Screen snippet from Anytone 878 CPS: