Start with the connection you have and the peers you want to reach. JSQ provides shared service meanings; the waveform and supported services must match at both ends. Explore the transport
FM / HF · Classic + Fast profiles
FSQ++ is our name for OpenJSQ’s FSQ enhancements: multi-slot conversations, CRC integrity checks, and stronger receive validation. FSQ Fast adds speed using more bandwidth.
FM · Experimental
A purpose-built packet waveform for ordinary FM voice audio. Explore higher data rates with selectable error protection.
FM · Standard packet compatibility
Use familiar 1200-bit/s AX.25 framing with existing packet equipment and digipeaters, or let OpenJSQ be the modem.
Verified direct chat is available on supported AX1200/JG25 links. Groups and relayed chat use Live. Capability discovery establishes which other services a peer offers. Delivery evidence · Service capabilities
FM / HF
Classic FSQ-2, FSQ-3, FSQ-4.5 and FSQ-6 preserve ordinary FSQ waveform compatibility, subject to the peer application’s framing and features. Use the conventional 1500 Hz position for fldigi/FSQCall and unknown peers.
Fast profiles are OpenJSQ extensions: wider tone spacing and faster signaling use more audio bandwidth. They need compatible support at both stations. A wider profile is a tradeoff, not a promise of a faster transfer on every path.
OpenJSQ’s multi-slot enhancement lets different stations hold concurrent conversations in separate parts of the passband at classic speeds. Here, FSQ++ names that capability—not a separate waveform.
Faster, wider profiles trade space for speed. Fewer slots fit as bandwidth grows; higher profiles use the whole channel.
Check for corruption on classic and Fast profiles. A CRC checks received data for errors. FSQ protects the sender callsign; OpenJSQ also supports an optional whole-message check. A CRC detects corruption—it does not repair it or prove delivery.
OpenJSQ checks candidate decodes before accepting them as messages, with the aim of reducing false decodes. Uncertain text stays marked unverified; failed validation is kept out of conversations. These receive checks complement multi-slot operation and CRC protection.
Separate stations can use clear narrow slots within the received audio passband. Wider Fast profiles leave less room for neighboring conversations.
Illustrative spacing, not exact frequencies, widths or a fixed slot count; capacity depends on the passband and profile. Each station transmits only one FSQ signal at a time. FSQ-6W can still share; FSQ-12 and higher operate as whole-channel profiles. Profiles and channel courtesy
The optional whole-message CRC is off by default for legacy compatibility: fldigi and FSQCall can display its extra check characters. Sender-callsign protection and whole-message protection cover different data.
Receive validation considers framing and integrity evidence. Checked traffic is eligible for automatic replies; unverified traffic needs operator approval and does not trigger automatic actions. Monitored candidates remain explicitly untrusted, and rejected decodes are excluded from conversations. Receive grades and controls · Decode Inspector
Ordinary lower-case text ranges from about 2 to 41 characters per second across the registered profiles. Capitals, digits and punctuation can take more symbols. These are character-rate estimates, not binary file speeds or measured end-to-end throughput.
FSQ is a single-carrier, constant-envelope, 33-tone waveform using differential incremental frequency-keying (IFK+) coding. The profiles use radio audio for FM / HF operation; the Fast profiles expand both symbol rate and tone spacing by an integer scale factor. FSQ Fast 4
Legacy compatibilityBandwidth scalingConfigure slots and audio
FM · Experimental
JG25 uses four-tone FSK through the normal microphone and speaker path, including FM emphasis and de-emphasis. It does not assume a flat high-speed data connector.
Choose a supported rate and error-protection setting for your radios and path. Both stations need compatible experimental builds; broader radio qualification remains in progress.
Jerome wanted a purpose-built format that leaves behind legacy AX.25 structure, aiming to spend less airtime on overhead and more on messages and files. That is a design goal, not a promise of faster delivery on every path.
The starting question was simple: 1200-baud AX.25 AFSK uses two tones—could more tones improve speed and reliability? Extensive testing through normal FM microphone and speaker paths, including pre-emphasis and de-emphasis, led to four-tone JG25 as the chosen speed/robustness balance among the designs tested, without requiring a flat 9600-baud data port.
JG25 is a separate on-air format. AX.25 equipment and standard KISS TNCs do not gain JG25 support simply because both modes use FM audio.
The seven modes run from 1,200 to 2,400 raw bit/s. Dividing by eight gives 150–300 bytes/s before frame overhead with no payload FEC; the half-rate FEC profile reduces that calculated body rate to 75–150 bytes/s. These are not measured file-transfer speeds.
| Mode | Baud | F0 | F1 (~3/4) | F2 (~2/3) | F3 (1/2) |
|---|---|---|---|---|---|
| JG1200 | 600 | 1200 | 900 | 800 | 600 |
| JG1400 | 700 | 1400 | 1050 | 933 | 700 |
| JG1600 | 800 | 1600 | 1200 | 1067 | 800 |
| JG1800 | 900 | 1800 | 1350 | 1200 | 900 |
| JG2000 | 1000 | 2000 | 1500 | 1333 | 1000 |
| JG2200 | 1100 | 2200 | 1650 | 1467 | 1100 |
| JG2400 | 1200 | 2400 | 1800 | 1600 | 1200 |
These are asymptotic payload rates while a data body is transmitting. The exact wire format also includes acquisition, a protected physical-layer header, frame integrity fields and coding termination bits. In OpenJSQ 1.0.0 the operator selects mode and FEC; the frame itself tells the receiver what was used. JG.25 6.2
FM · Standard packet
AX1200 uses standard AX.25 UI frames over 1200-baud AFSK. OpenJSQ can generate the audio itself, use Dire Wolf, or connect to a KISS-capable hardware TNC.
Serial and network KISS provide external connections. Bluetooth serial TNCs use the serial route; BLE KISS requires a compatible device and build support. Digipeating is distinct from JSQ application relay.
Suitable AX.25 digipeaters can forward OpenJSQ frames when radio/modem settings match and the configured route is supported by those digipeaters. OpenJSQ provides a Digipeater path setting for this link-level forwarding; it is separate from JSQ application relay.
Forwarding a frame does not require interpreting its JSQ contents. Mail custody, reliable files and other JSQ services still require a capable destination application. Not every APRS digipeater accepts arbitrary traffic or routes.
The Digipeater path is empty by default for simplex operation. Configure a suitable route for the network you intend to use; each hop repeats the frame and consumes airtime. APRS coexistence disables files, JSQ relay and automatic signal reports. Packet settings and coexistence
AX1200 carries 1,200 raw bit/s (150 bytes/s before overhead). Useful throughput is lower after framing, channel access, turnarounds and retries. Actual file-transfer speed depends on the setup and path.
Four profiles · Three modem families
FSQ is shown in ordinary lowercase characters per second; packet modes in raw bits per second. These native rates describe signaling, not measured file-transfer speed.
Classic · FSQ-6
≈5.9 chars/s
Classic FSQ compatibility at its fastest standard profile.
Fast · FSQ-42
≈41 chars/s
Seven times the FSQ-6 symbol rate, using more bandwidth.
Same text encoding; capitals, digits and punctuation can take more symbols.
AX.25 · AX1200
1,200 bit/s
Standard 1200-baud, two-tone AFSK packet.
JG25 · JG2400-F0
2,400 bit/s
Fastest documented JG25 FM profile, with no payload FEC.
JG2400-F3 trades half the nominal body rate for error protection: about 1,200 information bit/s before overhead.
Headers, error protection, channel turnarounds and retries reduce useful rates. The best profile is the one that completes the transfer on your path.
FSQ-6 sends 5.859375 symbols/s; FSQ-42 sends 41.015625. Ordinary lowercase letters use one FSQ varicode symbol, giving the rounded text estimates above during continuous text. Two-symbol characters, framing and service data reduce that rate. Binary files use their own transport encoding, so these values are not file bytes/s. FSQ profile registry · Character encoding
AX1200 sends one bit per symbol at 1200 baud. JG2400 sends two bits per symbol at 1200 baud. Its F0 body has no payload error-correction redundancy; F3 uses a nominal half-rate code, before termination bits and other overhead. Raw rate includes bits used for framing and service data, not just the user's message or file. AX1200 link · JG25 FM rates · JG25 protection
The specifications do not establish a common measured file-goodput comparison for these four profiles. A fair transfer test would need the same payload, radio path, service settings and retry accounting. The two groups therefore retain their own units.
The research follows candidate waveforms through simulations, rejected approaches and recordings from real radios. Explore the design history and the evidence behind the current experimental format.
Follow the guide for your hardware and make a direct test contact.