LMS-6 Radiosonde

The LMS-6 Radiosonde is a radiosonde manufactured by Lockheed-Martin Sippican, and used for meteorological sounding.

Overview

There are two models of the LMS-6, a 403MHz model and a 1680MHz model. This article will cover the 403MHz model unless specified.

Specs

• 16 Fixed transmit carrier frequencies (MHz): 400.250, 400.625, 401.000, 401.375, 401.750, 402.125, 402.500, 402.875, 403.250, 403.625, 404.000, 404.375, 404.750, 405.125, 405.500, 405.875
• Frequency tolerance +/-30ppm
• Mean TX Power 70.8mW (18.5dBm)
• Emission Designator 16K8F1D
• FSK with a maximum modulating frequency of 4.8 kHz
• Emission 3dB BW +/-5.0 kHz
• Emission 20dB BW +/-12.7 kHz
• Omnidirectional antenna
• Main beam gain 2dBi
• Horizontal Beamwidth 360 degrees
• Vertical Beamwidth +84 degrees

Source: https://apps.fcc.gov/els/GetAtt.html?id=121623&x=.

Photos

Relative Humidity Circuit section

Connectors

There are four sensor connectors (SENSN) used for sensor input by the radiosonde. SENS1 is not populated on the 403MHz units. SENS2-4 have leads connected to them, and the sensors are connected to the other end of the leads, outside of the radiosonde housing. Only SENS1 appears to have spacing for a connector; the others have arbitrary lead spacing.

SENS1 - 7-pin, 0.1" header spacing

Pin	Characteristics
1	+5V (5.47 measured)
2	GND?
3	+4.93V (Microcontroller VCC?)
4	1 Hz
5	1 Hz
6	1 Hz
7	GND?

Public information shows this header can be used for adding additional analog sensors to the radiosonde.

SENS2 - Humidity

Pin	Connection
1	Sensor pin 1
2	Sensor pin 2

0.3" spacing. Both lead wires have ferrite beads immediately before connecting to the board.

SENS3 - Temp. Sensor (standalone)

Pin	Connection
1	Sensor pin 1
2	Sensor pin 2

0.5" spacing.

SENS4 - Temp. Sensor (humidistat)

Pin	Connection
1	Sensor pin 1
2	Sensor pin 2

0.3" spacing. Fine gauge insulated wire run along SENS3 wire and loomed in white heat-shrink tubing.

Card edge - 40-pin, looks like ISA spacing

Pin Number	Function
1,2,7,8	U3 - Vdd | U15 - Pin 4
9, 10, 15, 16, 19, 20, 33, 34	Ground
3	U3 - ICCLK | TP33 | U21 - PCLK
4	U3 - Vpp/ICCSEL
5	U3 - RESET
6	U3 - ICCDATA
11	J5 - Pin 2
13	U3 - SW1.4
17	U3 - SW1.2
18	U3 - SW1.1
31	BATT POS
36	U3 - SW1.3
38	U3 - OCMP1_A / AIN10 / PF4
39	RED WIRE

J1 - 4-pin, 0.1" header spacing

Pin	Wire Color	Use
1	Black	Ground
2	White	Battery +9
3	Red	+9 VDC In
4	NC	Unknown - goes to unpopulated CR1

J4 - NC - earphone jack? uses SENS3 leads

J5 - 4-pin, 2.0mm spacing

Pin	Use
1	Unknown
2	Unknown
3	Unknown
4	Unknown

These traces go to U3 (ST microcontroller)

SP1 - 2x4-pin, 0.1" spacing

Pin	Use
1	Unknown
2	Unknown
3	Unknown
4	Unknown
5	Unknown
6	Unknown
7	Unknown
8	Unknown

These traces go to U14 (SPI mem?)

Components

GPS - Trimble 63530-50 s/n 1190122906

   https://www.trimble.com/embeddedsystems/copernicus2.aspx

U3 - 72F324J6T6 - ST72324 - Main Microcontroller, ST7 series

U5, U6 - LP2985

U?? - TPS7201Q

TPS7201Q on PCB

U13 - CD4040BPW

U14 - CD74HC4051PWR

U16 - LMV761

U21 - TI/Chipcon CC1050 (TSSOP 24)

U22 - TPS791

Sens 4 - Capacitive Relative humidity sensor

Notes

U13 Package marking shows CM040B. TI Park marking lookup provides CD4040BPW

U16 Package marking shows C22A. TI Part marking lookup provides LMV761. The SOT-23 footprint appears to match what is on the PCB.

Sens 4 is know to be capacitive since it is listed as such on page 13 of the WMO Common Code Tables Document

Circuits

RF from CC to Ant1 - coming soon

Relative Humidity Circuit

File:Relative Humidity Circuit Schematic.pdf U16 -Input also has a cap to ground not shown on the sketch.