LILYGO T-DECK Plus Frequency Settings & Allowable Bands (US 915 MHz)
I went to breakfast at That Place Downtown yesterday (Saturday). George Haneke (NV7Z) and Randy Holland (N5DDS) met me and much of our breakfast discussion was on the recent interest in Meshtastic. I had taken our LILYGO T-DECK Plus device with me and looking at at it’s settings, and knowing the nonlicensed frequency is 915 MHz, I was a little perplexed with some of the settings I found. Dr. Holland and I puzzled over it, I made a change and promptly bricked the unit. 🤣😂 When I got home I reflashed it and all is well, then I did some further review of things. 😎👍🏼
There is a slider that changes to things like LONG SLOW. Each one has a slightly different frequency, like 915.xxx. I wondered “What are the allowable frequencies?”
After digging into the Meshtastic documentation and FCC rules, here’s what I found:
Allowable Frequency Range (US / North America)
The LILYGO T-DECK Plus (915 MHz version with SX1262 LoRa module) operates in the 902–928 MHz ISM band. This is the standard unlicensed band for Meshtastic/LoRa devices in the US under FCC Part 15 rules. All of the preset slider options stay safely within this range.
The Slider (Modem Presets)
The slider options like Long Slow, Long Fast, Medium Slow, etc., are Meshtastic modem presets. They don’t just change the center frequency slightly — they adjust key LoRa parameters for different range/speed trade-offs:
– Bandwidth (e.g., 31.25 kHz up to 500 kHz)
– Spreading Factor (SF7–SF12)
– Coding Rate
Until yesterday I didn’t know any of that.
Meshtastic then uses a channel hashing algorithm based on the chosen preset and your Frequency Slot (0–n) to pick a specific center frequency like 915.xxx MHz. For example:
– LongFast (a very common default) often lands around 906–915+ MHz depending on the slot. There are ~100+ available slots in the US LongFast configuration.
– Slower presets (LongSlow, etc.) use narrower bandwidth and higher spreading factors for better range at the cost of lower data rates.
You can view or manually adjust the exact frequency and slot in the Meshtastic app (Android/iOS/web) or via the device’s web interface.
Recommendations for Our Group
– Set Region = US in the app. This enforces legal channels, power limits, and duty cycle rules.
– Start with LongFast for a good balance unless you need maximum range (then try LongSlow).
– Make sure your antenna is tuned for 915 MHz — a better antenna might make a big difference. Cliff Leath (KI5OPP) is experimenting with an 8db gain antenna. We will see what his experience is.
– Power is limited to +30 dBm (1W) ERP for unlicensed use, but most nodes run lower for battery life.
Legality Note
As long as we stay in the 902–928 MHz band with reasonable power and no interference, this is fully legal for unlicensed Meshtastic use (no ham license required, and encryption is allowed). For higher power or other bands we could explore licensed amateur radio operation on the overlapping 33 cm band.
If anyone else is setting up T-Deck Plus units, what preset and slot are you using? I don’t want to impose my will on anyone, but let’s standardize for better mesh interoperability.
73
Phillip Beall (W5EBC)