Freewave¶

The Freewave is a 900 MHz spread-spectrum RF radio modem used for short-range, high-speed communication with a Slocum glider. When the glider is on the surface within line-of-sight of a shoreside (or boat-side) Freewave, it gives you a fast, no-cost console — fast enough that no cable is needed for in-lab work, so most bench communication is done over RF rather than a direct connection.

Each glider carries a slave modem internally; you operate a master modem at the dock, in the lab, or on the recovery boat. The link is the glider operator's primary backup to Iridium: short range, but free and immediate when you can reach it.

Source

Paraphrased from the Slocum G3 Glider Operators Manual (Rev. 1, "RF Modem Telemetry" and Appendix F, "FreeWave Configuration"), the UG2 community Slack, and the Teledyne Webb Research user forum. Appendix F itself reproduces excerpts of the FreeWave Technologies Spread Spectrum User Manual — for the radios themselves, refer to FreeWave's documentation. This is a condensed field reference — always defer to the official Teledyne documentation for your specific glider.

Master and slave roles¶

The link is point-to-point: one master talks to one slave at a time.

Role	Where	Factory configuration
Slave	Inside the glider, on the flight Persistor	Set to call all masters
Master	Shoreside / lab / boat	Set to talk to one specific glider

The glider slave is factory-set to "call all", so any properly configured master can reach it. Teledyne strongly recommends never changing the slave configuration on the glider.
The master should never be set to "call all." You point each master at a specific glider by entering that glider's seven-digit Freewave serial number (from the glider's autoexec.mi) into the master's call book and selecting that entry.

Older gliders may not be set to call all

Some early units were not configured to call all, so a shared "emergency" master may fail to connect to them. Reconfiguring the slave is not trivial — it requires a special programming cable (one that can momentarily pull the setup pin to ground), and Teledyne's guidance is to contact glider support rather than reprogram the in-glider modem yourself.

Configuring a master to a glider¶

To point a master at a different glider (from Appendix F):

Connect the master to a computer's serial port and open a terminal program (e.g. PuTTY/HyperTerminal) at 19,200 N-8-1, no flow control.
Press the setup button next to the serial port on the back of the radio. The three board lights turn green and the Main menu appears.
Operation Mode (menu 0): set the radio as point-to-point master (0).
Baud rate (menu 1): setup is always 19,200, but set the radio's communication baud to 115,200 to match the glider link.
Frequency key (menu 3): set the key (the manual's example uses key 5). The master and slave must share the same frequency key.
Call book (menu 2): add the glider's seven-digit Freewave serial number into one of the 10 slots, then press C and select that entry to call. Do not select "A" (call all) on a master.
Press Esc to exit setup.

One master, many gliders in the lab

A common lab/yard setup is to keep one master permanently wired to the network and load several gliders into its call book, then switch which glider it calls as needed — rather than swapping modem boxes. This avoids cross-connecting to the wrong glider and means you never touch the glider-side slave.

A forgotten powered-on master will steal your comms

Because every glider slave is set to call all, any powered master whose call book contains your glider's serial can grab the link — and you won't know it. The classic time-sink: a second master left powered on a bench somewhere in the building, programmed to the same glider, intermittently steals the connection while you troubleshoot a glider that isn't actually broken. Operators have lost days to this. When comms are flaky in the lab, first confirm no other master (or another group's radio) is powered up and pointed at your glider.

Changing the glider-side baud or table needs a wired connection

You generally cannot reconfigure the in-glider Freewave through the RF link itself (you'd be cutting the very link you're using). Changing the glider's slave table or baud rate requires connecting directly to the modem board with the special cable. Note the baud the glider's Persistor uses to talk to its slave is independent of the baud between the master and your terminal emulator.

How to test the link¶

When both the glider and the master are powered and in range, the master's carrier detect (CD) light turns from red to green. A green CD is your quick confirmation that the RF link is up — this is also the standard bench test that the glider's comms board and Freewave module are alive.

consci — talking to the science Persistor over Freewave¶

The Freewave normally connects to the flight Persistor. To reach the science Persistor over the same radio:

From PicoDOS: type consci. This is a hardware-controlled hand-off. To return to the flight Persistor, the carrier must drop for three seconds — cut power to the master for about 10 seconds.
From GliderDOS: type consci. This uses a software-controlled connection (the "clothesline"); type quit to return to flight.

A successful hand-off changes the prompt from (GPICO)C:\> to (SCI)C:\>.

Freewave vs. Iridium during a mission¶

On the surface mid-mission, the glider prefers Freewave and falls back to Iridium:

On surfacing, the glider powers the Freewave console and looks for a carrier first.
If a carrier is found, it stays on Freewave and does not place an Iridium call.
If no carrier is found, it powers the Freewave off and dials in over Iridium.

Why a surfaced, in-range glider sometimes still calls Iridium

If the glider doesn't latch the Freewave carrier in that brief window, it will go to Iridium even though you're standing right there with a master. Issuing the callback command while in range usually establishes the Freewave connection. Note the behavior differs by state: from GliderDOS the glider can connect by Freewave and place its Iridium call at the same time; mid-mission it picks one.

Forcing the choice:

In mission, H is the in-mission shortcut for callback (e.g. h 0 0).
put c_iridium_on 1 turns Iridium on as a second console; for file transfers you can force the transfer over Iridium with the -f=irid flag, e.g. S -f=irid -num=3 *.sbd *.tbd. (When moving files, the Iridium phone hangs up and Freewave takes priority unless you force it.)
Surface-dialog argument force_iridium_use: 1.0 in a surfac*.ma file forces an Iridium call even while Freewave is connected — handy when simulating a mission on the bench: watch the dive over Freewave, drop master power at the GPS-fix point to trigger Iridium, then restore power to keep watching.

Power: the console and low-power drift¶

The Freewave console is a surprisingly large surface power draw. Operators report turning it off saved on the order of ~1 A·h per day on a glider drifting on the surface waiting for recovery.

c_console_on controls it:

Value	Behavior
`0`	Freewave console off
`1`	On at surface; powers off underwater after `u_console_reqd_cd_off_time` (default 15 s) with no carrier detect
`2`	On regardless (the usual default)

For a low-power surface drift far from any master, put c_console_on 0 is a meaningful saving; the starting-point mission nofly.mi is the canonical low-power surface-drift mission.
In mission, the console already turns off ~15 s after the surface check if there is no carrier (that's the "choosing Iridium" log line), so the savings there are smaller. In GliderDOS the Freewave is always on at the surface — this is where leaving it on really costs you.
Newer firmware exposes u_console_disabled_in_mission as a cleaner way to keep it off for low-power missions.

Turn the console back on before you send a boat

The Freewave is your in-range backup for recovery. If you take it out of service (use - console) or put c_console_on 0 to save power, remember to turn it back on before a recovery crew goes out expecting to home in on it. Also note: the operator does not have fine-grained control of Freewave power mid-mission — the surface behaviors constantly overwrite c_console_on as the glider climbs, fixes GPS, and chooses comms. Freewave is a critical device and cannot be taken out of service from GliderDOS with a glider on the pier.

Antenna placement and RF interference¶

Placement drives link quality — and a noisy Freewave can interfere with the glider's own sensors.

Height helps. A higher master antenna generally gives a better link.
Keep the master away from computers, phones, and other RF gear; even a ~2 ft move can clear up a noise problem.
For longer reach, FreeWave sells directional and omni antennas; band-pass / cavity filters help in extreme noise (near cell or pager towers).

Realistic range depends almost entirely on antenna height

Freewave is line-of-sight. From a ship's deck, expect roughly 0.5–1 mile. But operators using a directional Yagi raised up high — for example on a cliff or headland above the deployment site — have held a Freewave link 10–15 miles offshore. If you need range, get the master antenna high and pointed, not just bigger. Wave action that periodically blocks the line of sight will also cut in and out at the edge of range.

Freewave RF noise can trip pump and leak-detect faults

Several operators have traced bench and at-sea oddities — a deep/HD pump that misbehaves, spurious digifin leak-detect aborts ~300 s after surfacing — to RF interference from the Freewave coupling into the pump pot or leak-detect/pressure lines. Reported mitigations, with mixed success: use a good (outdoor coax-type) antenna and move it farther away; add ferrite beads to the antenna leads; physically separate the Freewave, Iridium, leak-detect, and pressure-sensor cabling inside the glider. For confirmed-noisy leak-detect, some operators (on Teledyne's advice) lower f_digifin_leakdetect_threshold to match the glider's background noise — values reported from ~980 to ~1015 are glider-specific. A few stubborn G3/G3S units never fully cleared and went back to Teledyne under warranty.

Field troubleshooting¶

Symptom	Things to check
In range, on surface, no Freewave (calls Iridium instead)	Issue `callback`; carrier may not have latched in the brief surface window. Confirm master powered and CD light behavior.
Master CD green in setup but dead outside setup (no lights, no comms)	Receiver may have failed — verify it works only in setup mode; if so the unit is likely toast and needs replacement.
Can't reach an older glider with a shared master	That glider's slave may not be set to "call all" / may have Slave Security on; needs the special cable to reconfigure (contact support).
Bench board powered but no Freewave comms	Confirm the glider-side modem has power — check voltage across the Freewave connector power pins; check TX/RX signal pins; confirm board is actually booting (a powered, booting flight board draws a few mA, not ~0).
Master not seen by Dockserver (rings, lights, but no pickup)	Confirm the right `/dev/ttyUSB*` is mapped to `freewave` in `dockServerState.xml`; verify you can reach the modem with `minicom` while Dockserver is stopped (rules out the cable/port).
Two gliders, one antenna	Operators have asked about a coax splitter feeding one antenna for dual-glider deployments — not a documented Teledyne setup; expect reduced link margin and test before relying on it.

Local terminal access

For direct low-level access you can talk to the glider over Freewave with a terminal program such as minicom (see the Dockserver notes), or use u4stalk for a glider terminal session. The radios run at 19,200 N-8-1 in setup mode regardless of the link's communication baud.