Hydra RF 424 824 924 Sub-GHz bands for Cardputer ADV

Hydra RF 424 vs 824 vs 924: Which Cardputer Sub-GHz Band Should You Buy? (2026)

PINGEQUA Lab · Hydra RF buying guide · 7 min read · Updated 2026-07-10

Hydra RF 424, 824 Pro, and 924 Pro all add Sub-GHz radio to the Cardputer ADV — the band you need depends on where you live and what you're talking to, not which one looks nicer.

Quick answer Pick by region and target-device frequency: 433 MHz for most of the world outside the Americas (Hydra RF 424, SKU CP-HYDRA-424, USD 32.99), 868 MHz for EU/UK SRD devices (Hydra RF 824 Pro, SKU CP-HYDRA-824, USD 35.99), or 915 MHz for the US/Canada/Australia/Latin America (Hydra RF 924 Pro, SKU CP-HYDRA-924, USD 35.99). All three are dual-radio CC1101 + nRF24L01+ caps for Cardputer ADV only, and a cap tuned for one band will not work well on another.

What all three Hydra RF caps share

Before the band decision, it helps to know that the 424, 824 Pro, and 924 Pro are the same platform underneath — only the Sub-GHz frequency and hardware refinement differ:

  • Dual-radio design: a CC1101 Sub-GHz radio paired with an nRF24L01+ 2.4 GHz radio in the same cap.
  • Cardputer ADV only: designed for the M5Stack Cardputer ADV. None of the three fit the original Cardputer v1.1 — see our ADV vs v1.1 compatibility breakdown if you're not sure which board you have.
  • Bruce firmware: all three run on Bruce and require a brucePins.conf setup to map the module correctly.
  • Auto-switching, hardware-level: mutual-exclusion circuitry switches between the Sub-GHz and 2.4 GHz radios automatically — there's no physical toggle switch to flip.
  • Host device not included: you supply the Cardputer ADV; the Hydra RF is the add-on cap.

If you want the fuller explainer on what CC1101 actually does on this platform, we covered it separately in what is a CC1101 cap for M5Stack Cardputer.

Decision table: 424 vs 824 Pro vs 924 Pro

Band SKU Price Region ISM allocation Typical devices
424 — 433 MHz CP-HYDRA-424 USD 32.99 ITU Region 1 (Europe/Africa/Middle East) license-free ISM/SRD; also the most common Sub-GHz band worldwide for consumer devices Key fobs, garage doors, sensors, weather stations
824 Pro — 868 MHz CP-HYDRA-824 USD 35.99 EU/UK SRD band, regulated under ETSI EN 300 220 and CEPT Rec 70-03 with duty-cycle limits EU/UK Sub-GHz consumer and IoT devices operating in the 863-870 MHz SRD range
924 Pro — 915 MHz CP-HYDRA-924 USD 35.99 902-928 MHz ISM band for the Americas, FCC-regulated US, Canada, Australia, and Latin America Sub-GHz devices in the 902-928 MHz range

Not sure a Sub-GHz cap is even the right module for your project versus other RF options? Our best RF module for M5Stack Cardputer comparison lays out the broader field.

Why the band choice actually matters

The CC1101 chip itself is a configurable Sub-GHz transceiver, but the antenna on each Hydra RF cap is physically tuned to one center frequency. That tuning is what makes the radio efficient at 433, 868, or 915 MHz — it isn't a firmware setting you can change after purchase.

A 433 MHz-tuned antenna performs poorly at 915 MHz, and vice versa. Band selection has to match both your region's legal ISM allocation and the frequency your target devices actually use — getting either one wrong means a cap that's compliant on paper but weak in practice, or the reverse.

424 vs 824 Pro vs 924 Pro: the hardware difference

Beyond the frequency, the 824 Pro and 924 Pro carry engineering upgrades over the 424's compact base design — but they are not identical to each other:

Feature Hydra RF 424 (base) Hydra RF 824 Pro Hydra RF 924 Pro
Band 433 MHz 868 MHz 915 MHz
RF chip CC1101 TI CC1101 CC1101
RF engineering Compact base design 50-ohm impedance-matched RF path, refined power path Transient-stabilized power rail, dual-chip PCB layout minimizing cross-talk
In the box Module only Module + 2 high-gain antennas + 3D-printed case Module + 2 high-gain antennas + 3D-printed case
Price USD 32.99 USD 35.99 USD 35.99

In short: the 424 is the compact, base-spec way into 433 MHz. The 824 Pro and 924 Pro are the "Pro" tier, but their upgrades differ — the 824 Pro adds a 50-ohm impedance-matched RF path, while the 924 Pro adds a transient-stabilized power rail and dual-chip PCB layout. Both aim at cleaner Sub-GHz performance, and both ship with two high-gain antennas plus a case rather than a bare module.

Region to legal band: matching your country

Framed as general ISM/SRD allocation information, not legal advice — always verify your local radio regulations before transmitting:

  • 433 MHz: license-free ISM/SRD in ITU Region 1 (Europe/Africa/Middle East, 433.05-434.79 MHz) per the Wikipedia "ISM radio band" overview and TI's ISM-band application note (SWRA048), and it's the most common band worldwide for consumer Sub-GHz devices. In the US, 433 MHz overlaps the 70 cm amateur radio band, though low-power unlicensed device use is common there under FCC Part 15 limits.
  • 868 MHz: the EU/UK SRD band (863-870 MHz), regulated by ETSI EN 300 220 and CEPT Recommendation 70-03, which impose duty-cycle limits.
  • 915 MHz: the 902-928 MHz ISM band used across the Americas (US, Canada, Australia, Latin America), regulated by the FCC under Part 15, per Wikipedia's "ISM radio band" entry.

Not legal advice — verify current allocations and duty-cycle rules with your own country's telecom regulator before transmitting.

Which one should you actually buy?

  • You're in Europe, the Middle East, or Africa working with typical consumer fobs/sensors: go with the Hydra RF 424 at 433 MHz — the most common band for this class of device.
  • You're in the EU/UK and specifically targeting 868 MHz SRD devices: the Hydra RF 824 Pro matches the ETSI EN 300 220 / CEPT 70-03 band and ships with the impedance-matched RF path plus two antennas and a case.
  • You're in the US, Canada, Australia, or Latin America: the Hydra RF 924 Pro covers the 902-928 MHz FCC ISM band with the transient-stabilized power rail and dual-chip layout.
  • You want the Pro-tier accessories (two high-gain antennas + case) regardless of band: choose between 824 Pro or 924 Pro based purely on your region/device frequency — the accessory package is identical, only the tuned frequency differs.

Match the band to your region and devices

All three Hydra RF caps require a Cardputer ADV and Bruce firmware with brucePins.conf configured.

Hydra RF 424 — 433 MHz Hydra RF 824 Pro — 868 MHz Hydra RF 924 Pro — 915 MHz

FAQ

Which Hydra RF band should I buy for my country?
Match your region's legal ISM/SRD allocation first, then check what frequency your target devices use. Broadly: 433 MHz (Hydra RF 424) suits ITU Region 1 — Europe, Africa, the Middle East — and is the most common band worldwide for consumer Sub-GHz devices. 868 MHz (Hydra RF 824 Pro) is the EU/UK SRD band under ETSI EN 300 220 / CEPT 70-03. 915 MHz (Hydra RF 924 Pro) is the FCC-regulated ISM band for the US, Canada, Australia, and Latin America. This is general ISM/SRD information, not legal advice — verify your local radio regulations.
Can one Hydra RF cap cover all three bands?
No. Each Hydra RF cap's antenna is physically tuned to a single center frequency — 433, 868, or 915 MHz. A 433 MHz-tuned antenna performs poorly at 915 MHz and vice versa, so band selection is a one-time hardware choice, not a firmware setting.
Is 433 MHz legal to use in the US?
433 MHz overlaps the 70 cm amateur radio band in the US, and low-power unlicensed device use at 433 MHz is common there under FCC Part 15 limits. This is general ISM/SRD allocation information, not legal advice — verify current FCC rules and your specific use case before transmitting.
What's the actual difference between the 424 and the 924 Pro?
Beyond frequency (433 MHz vs 915 MHz), the 424 is the compact base version — CC1101 module only. The 924 Pro adds a transient-stabilized power rail and a dual-chip PCB layout minimizing cross-talk, and ships with 2 high-gain antennas plus a 3D-printed case kit, versus the 424's module-only package. (The 50-ohm impedance-matched RF path is the 824 Pro's upgrade.)
Does Hydra RF fit the original Cardputer v1.1?
No. All three Hydra RF caps (424, 824 Pro, 924 Pro) are designed for the M5Stack Cardputer ADV only, not the original Cardputer v1.1. See our ADV vs v1.1 RF module compatibility guide for the full breakdown.

Sources & further reading: PINGEQUA product pages for Hydra RF 424 (CP-HYDRA-424), Hydra RF 824 Pro (CP-HYDRA-824), and Hydra RF 924 Pro (CP-HYDRA-924); Wikipedia, "ISM radio band"; Texas Instruments ISM-band application note SWRA048; ETSI EN 300 220; CEPT Recommendation 70-03; FCC Part 15. PINGEQUA is an independent manufacturer and is not affiliated with M5Stack, Bruce, Texas Instruments, Nordic Semiconductor, Semtech, or Meshtastic.

Frequency and ISM/SRD band information above is general reference material, not legal advice — always verify current radio regulations for your specific country before transmitting on any Sub-GHz band.

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