All beacons transmit using one antenna. The additional antennas are only active while searching at which time they play a significant role.

Steve Uncovers a Victim

Single Antennas

Single antenna transceivers typically have a long range when the searching beacon is in-line with the transmitting beacon's flux lines, but they have a significant loss in range when the antenna's are not aligned. Single-antenna beacons cannot display a directional indicator, although some single-antenna beacons do display a distance indicator.

Dual Antennas

Two-antenna transceivers have two antennas mounted perpendicularly. They compare the relative strength of the signal that is received on each antenna to calculate the location of the buried beacon. This allows the transceiver to guide you to the victim by displaying a directional indicator. Two-antenna beacons retain a strong signal even when they are turned 90°, because the second antenna is then aligned with the transmitting beacon's flux lines. Two-antenna transceivers, as with single-antenna transceivers, are unable to resolve spikes.

Three Antennas

Three-antennas transceivers have the advantages of two-antenna beacons (i.e., they can display a directional indicator), plus the third antenna (which only turns on when you get near the victim) can greatly reduce, or eliminate, spikes (where the beacon mistakenly points to a location a meter or two from the victim on deeper burials).

More About Multiple Antenna Beacons

The Tracker DTS was the first transceiver with two antennas. It quickly gained the reputation as the easiest avalanche beacon—it certainly was. The DTS uses its two antennas to display a directional indicator that points you toward your buried friend. Yes, some professionals discounted the Tracker as being for novices, but ease-of-use is important when your best friend is dying. The ARVA Advanced, ARVA Evolution+, and the Barryvox 3000 also have two antennas and as with the Tracker DTS, these beacons will quickly lead you to the victim. The Ortovox X1 also has multiple antennas (either two or three), but in my testing it performed relatively poorly.

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BCA Package

The ARVA Evo3, ARVA 3Axes, Ortovox S1,  Barryvox Pulse, Pieps DSP, Pieps DSP Advanced, and Tracker2 have three antennas. These avalanche transceivers not only offer the directional and distance benefits of two-antenna beacons, but they almost eliminate spike problems. You won't notice the spike handling when searching for a beacon a few inches under the snow (as is typical during practice), but bury it under a meter or two of snow and the difference is significant. Three antennas on a searching beacon ensure that antennas are pointed in three-dimensions (i.e., up/down, left/right, and forward/back). The beacon can then use the relative strength of the signal on each antenna to precisely locate the transmitting beacon. The Ortovox Patroller, Ortovox D3 and newer Ortovox X1s also have three antennas, but in my testing they did not accurately resolve spikes. The DSP (and probably others) has a 4th antenna that is only used during its self test.

In my testing, having two-or-more antennas is the most important factor in performing a rapid secondary search in a variety of conditions with a variety of rescuers. And three-antennas greatly improves the pinpoint search in all but very shallow burials. I know some old-timers will disagree, but only until they do serious tests with multi-antenna transceivers. I was a hardcore Ortovox F1 fan and swore that multiple antenna transceivers were for dummies—until I used one and discovered the benefits. That isn't a sales pitch, rather it is based on my experiences with many beacons.