RX Group List in practice: what your radio hears on a channel

There is one field in CPS that confuses people more than any other: the RX Group List (receive group). A beginner sees that the channel already has a "TX Contact" — the group your voice is sent to — and doesn't understand why another "group" is needed. Let's sort out what the RX Group List is for, how it works on a simplex hotspot, and why you shouldn't overload it.

TX Contact and RX Group List are different things

Every digital channel in a codeplug contains two independent fields for talkgroups:

• Contact (TX Contact) — the talkgroup your voice is sent to when you press PTT. One per channel.
• RX Group List — the set of talkgroups the radio listens to on this channel. It can include several groups at once.

A simple analogy: the TX Contact is "where I talk," the RX Group List is "who I hear." They aren't rigidly tied together. You can transmit to one group and receive from five different ones — all of them in a single RX List on the channel.

Why it matters in real life

Imagine your DMRhub network passes several active talkgroups to your hotspot — a general chat, a regional one, a group for QSOs. If the channel only has a TX Contact set (say, "General"), you'll only hear traffic from that one group. Everything else passes you by.

Add all the network groups you need to the RX Group List and a single hotspot channel becomes an "ear" for the entire network at once. You'll still transmit to one TG (via the TX Contact field), but you'll hear all the current traffic.

Limits and structure of the RX Group List

The maximum size of one RX Group List is 32 talkgroups. In practice, that many is overkill for a personal hotspot. A few dozen active groups at once will create chaos on the air: the radio will keep unmuting constantly.

Typical ways to fill it:

1. One list — one TG (1:1). You create a separate list for each channel and put exactly one TG in it. The list is essentially decorative here — the radio hears the same thing as the TX Contact. Handy if you want to isolate a channel.
2. A shared list for the slot. You add all the TGs you need from the hotspot/repeater into one list. You then attach the same list to several channels. This saves time when the network's active groups change — you edit it in one place.

Promiscuous mode (Digital Monitor)

Some radios support Digital Monitor (called "Promiscuous Mode" or "Digi Monitor" in other firmwares). In this mode the radio unmutes on any traffic on the current frequency with a matching Color Code — regardless of whether the incoming TG is in your RX Group List or not.

This is handy for monitoring an unfamiliar repeater or debugging a hotspot: turn the mode on and you hear everything. But it's inconvenient for everyday use: the radio will react to any transit traffic. That's why Digital Monitor is usually turned on temporarily — for diagnostics.

Common setup mistakes

An empty RX Group List

If the channel's RX Group List field is empty (or set to "None"), the behavior depends on the firmware. On most radios it means the radio only hears the current channel's TX Contact. On some, it stays silent on any traffic. It's always better to explicitly assign a list.

A timeslot mismatch

The RX Group List only works within a single timeslot. If the hotspot carries traffic on TS2 but the channel is set to TS1, the radio won't hear anything, no matter how many TGs you add to the list.

A list that's too big

Adding every conceivable TG "just in case" is a bad idea. The DMRhub network isn't isolated from worldwide traffic: under certain conditions, foreign groups can pass through the hotspot. A stuffed list turns your radio into a scanner — it will unmute on any activity. Keep only what you actually need in the list.

The list exists, but the hotspot's TG isn't in it

A classic: you built a nice list, assigned it to the channel, but forgot to add the network's main TG — the one that arrives from the hotspot. The radio stays silent. Always make sure the channel's TX Contact is also present in the RX Group List.

Example: a DMRhub hotspot channel

Here are the typical settings for a digital channel for a RadioStar simplex hotspot:

Channel name:  DMRhub General
RX frequency:  438.8000 MHz
TX frequency:  438.8000 MHz  (simplex — same as RX)
Timeslot:      TS2
Color Code:    1
TX Contact:    DMRhub General  (network TG, see /contacts)
RX Group List: DMRhub HS       (list with all active network TGs)
Admit Criteria: Always

The DMRhub HS list then contains the TGs whose traffic interests you on the hotspot: the general chat, the regional group, and so on. For the exact TG numbers, check the contacts section of your dashboard — they're current and always match what's configured on the server.

How to add a TG to the RX Group List: the general procedure in CPS

1. Make sure the TGs you need are already created as Contacts (type — Group Call).
2. Go to the RX Group List section (Digital → RX Group List in most CPS).
3. Create a new list and give it a meaningful name (for example, DMRhub HS).
4. Move the TGs you need from the "Available" column to "Members" (the arrow button or a double-click).
5. Save the list.
6. Open the desired channel → the RX Group List field → select the list you created.
7. Write the codeplug to the radio.