Understand your Spektrum telemetry

Radio link: frame losses, fades and holds

The receiver counts what goes wrong on the radio link:

• Frame losses are frames that did not arrive on any antenna. A few are normal. TLMscope rates up to about 20 per minute as high quality and up to about 100 per minute in the air as normal, in line with Spektrum receiver manuals.
• Fades are short dropouts on a single antenna (A and B, and L and R for remote receivers). The count per antenna shows which one is shadowed by the airframe.
• Holds are about a second without any signal. The receiver then goes to its hold or failsafe setting. A hold in flight is always rated critical.

These counters start at zero when the receiver powers up. TLMscope shows what happened during the session.

Signal strength

The signal strength at the receiver is given in dBm: the closer to zero, the stronger. In TLMscope's own sample flights, frame losses rose sharply below about −80 dBm. It therefore rates −70 dBm or better as high, down to −80 dBm as normal, down to −85 dBm as weak and anything lower as critical.

The Radio link tab plots the signal against height, because height and distance often go together.

Receiver voltage

The voltage at the receiver should stay steady under load. TLMscope rates 5.2 V or more as steady, 4.8 V or more as OK, anything above 4.0 V as dips and below that as brown-out risk. Look for dips when several servos move at once. The AR8360T manual asks to stay above 4.8 V under load, and receivers of this family drop out below about 3.5 V.

Battery: charge used, cells and internal resistance

• Charge used is the share of the pack's capacity drawn in the session. TLMscope rates up to 50 % as plenty left, up to 70 % as fine, up to 80 % as land soon and more as over-drawn: the common 80 % rule.
• Cell voltages from a Spektrum Smart battery show the lowest and highest cell. A growing difference between cells points to an unbalanced pack.
• Internal resistance per cell is estimated from how far the voltage sags when the motor draws current, so it includes the wiring. Under 10 mΩ per cell is excellent, up to 12 mΩ acceptable, and above 15 mΩ it is time to retire the pack, a rule of thumb from LiPo guides. The Batteries page follows this value from flight to flight and estimates how many charge cycles are left.
• Temperature of 35 to 45 °C after a flight is normal. TLMscope warns from 45 °C and treats 60 °C as the usual ceiling.

Motor and speed controller

Smart speed controllers such as the Avian report motor current, input voltage, throttle, rpm and temperatures. TLMscope uses them to find the motor runs, to work out the charge used per minute in the air and the height gained per 100 mAh in motor climbs.

Height, climb rate and thermals

A vario or altimeter sensor reports height and climb rate. TLMscope splits a flight into motor climbs, glides and lift: climbing with the motor off for about ten seconds or longer is marked as lift. The centres of thermals are estimated from circling flight and shown on the map.

Loads and rotation

Receivers with AS3X or SAFE report loads in g and rotation rates. TLMscope uses them to detect circling and to tell how gentle or sporty a flight was.

Frequently asked questions