ExpandedBasicTelemetry (Draft) - HdrType=2

Overview

Draft

ExpandedBasicTelemetry is draft and subject to change.

The purpose of ExpandedBasicTelemetry (HdrType=2) in Extended Telemetry

Carries an expanded range of measurements from those originally available within BasicTelemetry.

Summary of change

Field	ExpandedBasicTelemetry from BasicTelemetry Compare
Temperature	Shifted/Lower -60F to 70F range (from -58F - 102F)
Voltage	Wider 1.8v to 7.0v range (from 3.0v to 4.95v)
GpsValid	Unchanged
GPS Location	9% improved accuracy by using non-maidenhead grid scheme
Altitude	Wider 0 ft - 120,000 ft range (from 0 ft - 70,000 ft)
Speed	Dropped in lieu of receiver GPS speed calculation

Message Structure

The header, as explained in Header Fields, explains the whole message header structure.

The fields below are for when the HdrType=2 indicating an ExpandedBasicTelemetry message.

Link to Message Definition

The ExpandedBasicTelemetry message makes use of both Uniform and Segmented Field Encoding

Segmented fields are described in more detail below the message definition table.

The structure of the ExpandedBasicTelemetry fields

Field	Unit	LowValue	HighValue	StepSize	# Values
Temperature	F	-60	70	[segmented]	32
Voltage	V	1.8	7	[segmented]	44
GpsValid	Bool	0	1	1	2
Latitude	Idx	0	15	1	16
Longitude	Idx	0	35	1	36
Altitude	Ft	0	120,000	[segmented]	374

Field Temperature

A segmented field, so variable resolution within the range of values.

Field Calculator

Temperature Segments

Segment	Description
[-60, 5, -30]	Cold-end range, where a coarser resolution is acceptable
[-30, 3, 30]	Middle range, where temperature changes are more operationally useful
[30, 8, 70]	Hot-end range, where a broader step is acceptable

Field Voltage

A segmented field, so variable resolution within the range of values.

Field Calculator

Voltage Segments

Segment	Description
[1.8, 0.300, 3.0]	Low-voltage region, where only coarse resolution is needed
[3.0, 0.0625, 5.0]	Main operating range, with the finest resolution
[5.0, 0.200, 6.0]	Elevated-voltage region, where coarser resolution is acceptable
[6.0, 0.500, 7.0]	Extreme high-voltage region, where only broad visibility is needed

Field GpsValid

Same boolean yes/no.

When no, no meaning is defined for the GPS-sourced data

This applies to:

• Latitude
• Longitude
• Altitude

Field Location (LatitudeIdx and LongitudeIdx)

These fields are identical to those in HighResLocation in behavior (not value)

Read over the spec for HighResLocation to see how use these field values.

Comparing Resolution

Moving to a 36 x 16 Idx scheme intead of Grid56 brings better 2D accuracy for equal bits.

Dimension	Idx scheme (36 × 16)	Grid56 (24 × 24)
Width (east-west)	3.83 miles (20,240 ft)	5.75 miles (30,360 ft)
Height (north-south)	4.31 miles (22,770 ft)	2.88 miles (15,180 ft)
Center error (E-W)	± 10,120 ft	± 15,180 ft
Center error (N-S)	± 11,385 ft	± 7,590 ft
Worst-case error (diagonal, equator)	± 15,200 ft (2.9 mi)	± 16,950 ft (3.2 mi)

Field Altitude

A segmented field, so variable resolution within the range of values.

Field Calculator

Altitude Segments

Segment	Description
[0, 75, 3300]	Low altitude region, with fine resolution for takeoff and landing
[3300, 300, 33000]	Climb and cruise-to-near-float range, with moderate resolution
[33000, 75, 45000]	Float range, with fine resolution where balloon operation is common
[45000, 500, 60000]	High-altitude region, where less fine visibility is sufficient
[60000, 1500, 120000]	Extreme altitude region, where only broad coverage is needed

Segment range for first 3 segments (last two ignored to reveal scale better)

When this message can be sent

Scheduling

Slots 2, 3, 4, 5 in the same window that the referenced 4-char Maidenhead grid is found in.

Ok to send in multiple slots in the same window (ie with new or repeated location).

If the 4-char grid changes (eg with new location) it is not appropriate to send the new refinement as it no longer references an established 4-char grid. Re-sending old refinements are ok in that scenario.