Yagi + TeleBT + iPhone for range

At a normal club launch the stock setup is fine: a TeleBT v4 with its stock whip antenna, paired to an iPhone running AltosUI. For long-distance launches — high-altitude attempts, desert waivers, anywhere the airframe is going well past typical range — a directional yagi antenna on the TeleBT can extend the link enough to keep telemetry flowing through apogee and descent. In that configuration the TeleBT normally rides on the yagi itself via a 3D-printed bracket, so the receiver and the antenna move together when you track the rocket. This is a field-practice note about how that combination fits together, not an antenna-theory post.

What a yagi actually does

A yagi is a directional antenna. Instead of radiating and receiving roughly equally in all directions, it concentrates sensitivity along the direction it’s pointed. Point it at the rocket and it picks up a weaker signal than an omnidirectional antenna would; point it away and it picks up almost nothing. At range, that directional gain can be the difference between a solid packet stream and dropouts.

The trade is that you have to point it. A yagi is not “set it down and forget it” — someone holds it or mounts it on a tripod, and someone tracks the rocket as it moves. At a high-altitude flight that typically means following it up, past apogee, and along the drift until landing. If tracking wanders, the signal drops.

How it connects to TeleBT v4

The TeleBT v4 is the only supported ground station for AltosUI iOS over Bluetooth LE. It ships with a small stock whip antenna on the receiver’s SMA connector — fine for a typical club launch. A yagi is not included; you order one separately, sized for the 70 cm band, from whichever supplier you prefer. Once you have one, you unscrew the stock whip and connect the yagi in its place. There’s nothing iOS-specific about the swap — it’s the same TeleBT antenna configuration you’d use on any ground station.

One practical note on connectors. TeleBT uses SMA, and several popular hand-held yagis — the Arrow among them — use BNC at the feed point. If your yagi is BNC-terminated you’ll want an SMA-to-BNC adapter between the receiver and the antenna. The AltOS Owner’s Manual describes exactly that pairing — TeleBT plus SMA-to-BNC plus a hand-held yagi — as a strong ground-station configuration.

Most fliers don’t carry the TeleBT separately once a yagi is in play. Altus Metrum publishes a 3D-printable mount that clips the TeleBT directly to an Arrow yagi (see altusmetrum.org/TeleBT/), and other clubs have printed their own brackets for other yagis. The point is the same either way: the receiver rides with the antenna so the coax run is short and the two track together when you follow the rocket.

Altus Metrum’s hardware notes for the TeleBT line live at altusmetrum.org/TeleBT/. That’s the authoritative source for connector types, supported bands, and anything electrical about the receiver itself.

What changes on the iPhone side

Nothing. The iPhone’s job in this setup is unchanged: it pairs to the TeleBT v4 over Bluetooth LE and receives demodulated telemetry the same way it always does. There’s no iOS-side setting for antenna type, no “yagi mode,” no calibration step. AltosUI sees whatever packets the TeleBT decodes and drives the Pad, Flight, Map, and Recover tabs off them.

In practice that’s exactly what you want — the app doesn’t care how the packets got into the receiver, only that they did. If the yagi is doing its job the app will just show you a cleaner, more continuous telemetry stream at long range. You may see fewer gaps in the Recovery Map track, a later last-reported position, and shorter signal-loss warnings in the Flight Report.

Practical field notes

Plan the handoff. If one person is running the phone and another is holding the yagi, agree beforehand who calls bearing and who watches the screen. Voice callouts from AltosUI help — they narrate state transitions and peaks while the pointer tracks the sky.
Pre-aim. Before launch, point the yagi up the expected flight path. The beam is directional; the more accurately it’s pointed during boost, the better the boost-phase signal.
Track through apogee and drift. The rocket doesn’t stop where the boost ends. Keep tracking through descent — that’s where you’ll want the extra gain to preserve a clean last-reported position for recovery.
Don’t overtighten your grip on the phone. The iPhone is still doing the same pairing it always does; BLE range to the TeleBT is short regardless of the antenna on the RF side. Keep the phone within a few meters of the receiver.

Amateur radio license

More reach means more reason to be properly licensed. To legally operate an Altus Metrum flight computer in the US, you need at least a Technician-class amateur radio license. This isn’t a yagi-specific requirement — it applies any time you’re flying a TeleMetrum, TeleMega, or TeleGPS — but when you’re putting a directional antenna on the receiver you’re specifically building out a ham-radio station, and it’s worth pausing on that.

Altus Metrum’s radio page is at altusmetrum.org/Radio/. The ARRL’s licensing and education page is the standard starting point for the Technician exam.

What this post doesn’t cover

This isn’t antenna theory, it’s not an antenna-brand shopping guide, and it’s not a recommendation of specific yagi products. Which antenna is right for your setup depends on the band, the mount, the connector, the frequency coordination at your field, and local regulations — all of which are outside the scope of an app guide. Talk to the experienced fliers at your club and read the Altus Metrum radio page for the hardware-side specifics.