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Meshtastic Channel Number Selection Guide

Meshtastic'sMeshtastic channelhas numbertwo settingdistinct controlsconcepts that are easy to confuse. The LoRa Frequency Slot (lora.channel_num) selects the exactsingle center frequency ofthe LoRaradio transmissionstransmits withinon. This is separate from the regulatoryup-to-8 band.logical ChoosingChannels (each with its own name and PSK, indexes 0–7), which all share the rightsame channelfrequency. numberAdding canlogical reducechannels interferencegives withyou otherseparate usersencrypted andmessage allowstreams multiple— independentit networksdoes not change your RF frequency, provide RF isolation, or avoid collisions. Only changing the frequency slot (or the modem preset) actually moves you to coexista peacefully.different frequency.

How Channelthe NumbersFrequency WorkIs Chosen

Meshtastic calculatesdoes not compute the center frequency from thea logical channel number,number modemusing a simple base + spacing formula. Instead, the firmware divides the region's band into a fixed number of frequency slots (slot width = the preset's bandwidth) and picks one slot:

    If lora.channel_num is 0 / UNSET (the factory default), the firmware computes a hash of the PRIMARY channel's NAME (a djb2 hash in RadioInterface.cpp) and uses it to select a slot. If lora.channel_num is set to 1–104, that value is an absolute slot index and overrides the name hash.

    For the US 902–928 MHz band with the LongFast preset, andthe region:bandwidth is 250 kHz, which yields 104 frequency slots of 250 kHz each across the 26 MHz usable band. (125 kHz is the bandwidth of the Long Moderate / Long Slow presets, not LongFast — those presets have more slots.)

    # For US region withregion, LongFast preset
# Bandwidth (125slot width): 250 kHz
BW)# Number of frequency slots: 104

# Default channel_num = 0/UNSET -> frequency comes from a HASH of
# the PRIMARY channel NAME, NOT from a linear base+offset formula.
# The default LongFast channel name hashes to slot 20 = 906.875 MHz.

# Slot-to-frequency formula (only when you set an explicit slot):
#   Basefreq_MHz frequency:= freq_start + (slot * bandwidth) + (bandwidth / 2)
# US: freq_start = 902.0 MHzMHz, bandwidth = 0.250 MHz, slot is 1-based (1..104)
#
Channel# spacing:Example, default LongFast slot 20:
#   902.0 + (20 * 0.250) + 0.125 MHz... (125is kHz)reached via the name hash,
#   Centergiving frequencythe =documented Basedefault +of (channel_num906.875 *MHz.
    spacing)

    Note +that offset # Channel 0: 906.875 MHz (default)corresponds #to Channelfrequency 1:slot 907.000 MHz # Channel 2: 907.125 MHz # ... # Channel 7: 907.875 MHz # For MediumFast20 (250the kHzresult BW):of #hashing Channelthe spacing:default channel name), not "channel 0.25" MHzThere #is Channelno 0:base 906.875902.0 MHz+ #channel Channel× 1:0.125 907.125linear MHzprogression, and the slot index is not limited to 0–7 — those are the logical channels, a completely separate concept.

    Why Change the Default Channel 0?Slot?

    Most Meshtastic nodes ship withon channelthe 0default asLongFast default.channel, which hashes to slot 20 (906.875 MHz). If your area already has significant Meshtastic traffic already,traffic, you may benefit from staying on channelthe 0default to maximize connectivity with existing nodes. However, if:

    • You're running a private community network that doesn't wantwants to receiveoperate oron interfereits withown strangersfrequency (note: changing frequency means those nodes can no longer hear the default mesh, and vice versa)
    • You've identified interference at the default frequency with an SDR
    • You want to operate on a less crowded frequency in a dense metropolitan area

    ...then changingsetting an explicit frequency slot (or choosing a different primary channel name that hashes to a different channel numberslot) makes sense. Changing logical channels alone will not do this — logical channels all share the same frequency.

    Channel NumberFrequency Coordination

    WithinFor all nodes in your community network,network allto nodeshear each other, they must usetransmit on the same channelfrequency number— (along withmeaning the same modem preset and the same frequency slot (which means either the same primary channel key)name, since the name-hash sets the slot, or the same explicitly set lora.channel_num). They must also share the same channel name/PSK to decode each other's traffic. Keep a community coordination document:

    # Check current channelfrequency number:slot:
meshtastic --get lora.channel_num

# Set channelan number:explicit frequency slot (absolute slot index, 1-104 for US LongFast):
meshtastic --set lora.channel_num 3

# CalculateThis actualselects centerfrequency frequency:SLOT 3, an absolute slot - NOT an offset added
# US, LongFast:to 906.875875. For US LongFast (250 kHz):
#   902.0 + (3 * 0.125)250) + 0.125 = 907.250903.375 MHz
#
# Setting channel_num to 0 reverts to the channel-name hash (default).

    Bandwidth and ChannelFrequency-Slot Separation

    For twoTwo independent networks on the same band coexist by transmitting on different frequency slots (set via different slot numbers, or different primary channel names that hash to havedifferent trueslots). Separating two networks by ≥2 slots reduces adjacent-channel interference, but it does not give complete RF isolation,isolation their— channelsLoRa's needspectral toskirts beextend separatedbeyond bythe at least 1x theirnominal bandwidth and the 902–928 MHz band is shared ISM spectrum, so some interference is always possible. (125Separate kHzchannel fornames/PSKs LongFast).alone provide only logical separation — same frequency, same airtime, same collisions.) Practical guideline:

    Modem PresetBandwidth (slot width)Min Separation for Isolationsubstantial isolation
    LongFast125250 kHz2≥1 channel numbersslot (250 kHz); ≥2 slots (500 kHz) for better margin
    MediumFast250 kHz≥1 slot (250 kHz); ≥2 channel numbersslots (500 kHz) for better margin
    ShortFast250 kHz≥1 slot (250 kHz); ≥2 channel numbersslots (500 kHz) for better margin
    ShortTurbo500 kHz≥1 slot (500 kHz); ≥2 channel numbersslots (1000 kHz) for better margin

    If two networks operate on adjacent channelsslots with the same bandwidth, they'll still experience some co-adjacent-channel interference butand won't be completely isolated. ForRemember mostthat communityputting situations,your 2network channelon numbersa separationdifferent isfrequency sufficient.slot from the local default mesh means the two networks can no longer relay for each other — that's the intended trade-off when you want a private frequency.

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