Auto Mode: Letting the Scanner Pick AM, NFM or DMR

Auto is a channel mode alongside AM, NFM and WFM. Instead of you telling the scanner how a channel is modulated, the engine listens to each stop and decides for itself — AM, NFM (narrow or wide), DMR digital voice, or, in Radio mode, WFM broadcast. It’s meant for the bands where modes are mixed: 137–144 MHz, 150–174 MHz marine and business, 400–470 MHz, and any scan list that mixes airband with repeaters or PMR.

Where to Set It

• Scanner tab — the Mode dropdown on the Scan Source card, for a frequency-range sweep.
• Bands tab — each band’s Mode column.
• Scan Lists tab — each entry’s Mode.
• Radio tab — the VFO’s Mode dropdown. Auto isn’t offered for SSB or CW, which have no carrier to measure.

How It Decides

When the scanner parks on an Auto channel, the engine demodulates it as AM and as FM at the same time and watches for the DMR sync pattern:

• Two DMR syncs — it’s DMR, and the native DMR decoder takes over.
• Three frames in a row reading clearly AM (a plain carrier counts as AM) — AM.
• FM reading above AM and above the noise — NFM; a signal with wide deviation gets the wider FM filter.

On an open channel it usually decides within about 0.6 seconds, and never takes longer than 1.5 seconds; if it still can’t tell, the band’s expected mode wins. You don’t lose the start of the call: both demodulators run until the decision is made, then the chosen one goes live and the audio it kept is replayed.

What You See

• The Now-Listening panel reads Auto… while it’s deciding, then the result, e.g. NFM · auto or DMR · auto.
• The engine’s hit rows and the Squawker Connect log carry the mode it chose, e.g. DMR (auto) — so a logged transmission records how it was actually modulated.

What It Expects Per Band

The engine starts each decision with an expectation, so a borderline reading doesn’t flip the mode on a band where one answer is nearly always right. Your Bands tab is sent to the engine for this: on an Auto channel inside one of your listed bands it leans toward that band’s mode (AM in the air bands, NFM for business, marine and amateur, WFM for broadcast) and needs clearer evidence to go the other way. Outside your listed bands it uses a built-in UK table — 87.5–108 MHz WFM, 108–144 and 225–400 MHz AM, everything else NFM. A band whose own mode is Auto gives no lean.

Auto in Radio Mode

With the VFO’s Mode on Auto, every squelch opening is probed on the side. The first opening after you tune is held and replayed in the mode chosen; later openings play on in the last mode and switch only if the probe disagrees. Radio mode can also recognise WFM — a signal occupying more than about 50 kHz is a broadcast station, and the audio path switches to wideband for it. The mode chosen shows beside the Mode box, and the Bandwidth box is greyed, because the engine picks the filter.

Limits

• Only DMR is told apart among the digital modes. P25, NXDN, TETRA and other digital signals read as NFM and you’ll hear them as noise — lock them out as usual.
• On a pure airband sweep there’s nothing to decide; set AM and save the engine the probe.
• SSB and CW are never chosen, so for HF utility and amateur listening pick the sideband yourself.