DMRhub hotspot channel by hand: frequency, CC, TS2, contact

A ready-made codeplug for your radio model gets you started much faster, but sooner or later you have to add channels by hand: you changed the hotspot frequency, you are setting up a second hotspot, or you simply want to understand exactly what lives in each field. This article is a complete breakdown of every parameter of a digital channel for a simplex MMDVM hotspot. It applies to OpenGD77, AnyTone AT-D878UV/AT-D868UV, TYT MD-380/390 and other DMR radios.

What a simplex hotspot is and why it matters

A standard MMDVM-based hotspot (HS_Hat, Nano-Hat, DVMEGA boards and the like) operates in simplex mode: the radio and the hotspot talk on the same frequency. This is not a repeater, where RX and TX are split by an offset. Hence the first and most important rule: in the channel, the RX Frequency and TX Frequency fields must be identical.

A simplex hotspot works in so-called DMO mode (Direct Mode Operation) at the RF interface level. This carries one more fundamental consequence — about the time slot, covered below.

Where to get the parameters: your DMRhub account

Before opening the CPS, log in to your DMRhub account. There, in your hotspot's section, you will find three key parameters that cannot be guessed — the server assigns them when the device is registered:

• Frequency — the one you chose when setting up the hotspot (or the one the system recommended for your band);
• Color Code (CC) — a numeric identifier of the network "cell", the digital equivalent of CTCSS in analog;
• Talkgroup list — which group calls are available on your server.

Channel fields, one by one

RX Frequency and TX Frequency

Both fields are the same number. For example, 433.450 MHz. In the 70 cm amateur band the usable range is 430–440 MHz, so pick a frequency within it. For the 2 m band it is 144–146 MHz.

Color Code

Color Code (CC) is a number from 0 to 15. If the radio and the hotspot have different CC values, there will be no link: the hotspot simply ignores the RF traffic. It is the equivalent of a CTCSS tone — no match, no sound. The value must match exactly what is set in the MMDVM config on your hotspot.

Time slot: always TS2

A simplex hotspot is a Tier I device: it does not split the channel into two independent time slots. From the server's point of view, all traffic from a simplex hotspot is always handled as Time Slot 2 (TS2). If you set TS1 in the channel, the radio will transmit but the server will reject it as "RF rejected". There will be no link.

Contact (TX Contact)

This is the talkgroup your voice goes to when you press PTT. You need to add the matching TG in advance in the codeplug's "Contacts" section (type — Group Call, number — from your DMRhub account). One channel = one primary Contact. If you want to use several groups, create several channels on the same frequency that differ only in this field.

RX Group List

The set of talkgroups the radio will receive on this channel in addition to the primary Contact. If you want to hear several groups at once, add them to an RX group and assign it to the channel. If you only need to receive one TG, you can choose "None" or make an RX group with a single entry.

Admit Criteria

This is the condition under which the radio allows itself to key up on PTT. For a hotspot the correct choice is Always. The "Channel Free" value suits repeaters with live traffic, where you need to yield to someone else's QSO. On a personal hotspot the "wait for silence" logic only gets in the way.

Summary table: quick reference

For convenience, all fields in one place. Take the specific frequency, CC and TG values from your DMRhub account.

Field              Value for a simplex hotspot
-------------------------------------------------
RX Frequency       = TX Frequency (simplex!)
TX Frequency       desired frequency, 430–440 MHz
Color Code         from MMDVM config (usually 1)
Timeslot           TS2 (TS2 only!)
Contact (TX)       desired talkgroup (Group Call)
RX Group List      list of TGs to receive
Admit Criteria     Always
Channel Mode       Digital

Example: three channels on one hotspot

Suppose your hotspot is on 433.450 MHz, Color Code 1. You want three separate channels: a local group, a regional group and a private call to a friend.

Channel 1: "Local"
  RX/TX: 433.450
  CC: 1, TS: 2
  Contact: TG "Local" (Group Call)
  RX Group: local+region
  Admit: Always

Channel 2: "Region"
  RX/TX: 433.450
  CC: 1, TS: 2
  Contact: TG "Region" (Group Call)
  RX Group: region
  Admit: Always

Channel 3: "Private"
  RX/TX: 433.450
  CC: 1, TS: 2
  Contact: colleague's DMR ID (Private Call)
  RX Group: None
  Admit: Always

Put all three channels into a single "Hotspot" zone and scroll through them with the encoder.

Common mistakes and symptoms

• No outgoing link, the hotspot stays silent — most likely the wrong Color Code or TS1 is set. Compare both parameters with the MMDVM config.
• The radio "hears" the hotspot, but the server rejects the call — that very "RF rejected". The cause is TS1 in the channel. Change it to TS2.
• The hotspot responds, but you only hear yourself (echo) — this is normal diagnostics; it means the RF part works. Check that the Contact is set correctly and that the TG is available on the server.
• The radio "stalls" before transmitting — Admit Criteria is set to "Channel Free" or "Color Code Free"; change it to "Always".