LMS-6 Radiosonde

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Revision as of 20:41, 5 September 2020 by Paul Rixon (talk | contribs) (Added TX output schematic; instructions on how to disable amplifier.)
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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 Notes / Observations
1,2,7,8 U3 - Vdd | U15 - Pin 4
9, 10, 15, 16, 19, 20, 33, 34 Ground
2, 8, 18*, 24, 30 +5VDC 18 needs more research, may occasionally drop to ground?
3 U3 - ICCLK | TP33 | U21 - PCLK
4 U3 - Vpp/ICCSEL
5 U3 - RESET
6 U3 - ICCDATA
11 J5 - Pin 2
12 3.3v - 2.5KHz square wave (4msec p/p)
13 U3 - SW1.4
17 U3 - SW1.2
18 U3 - SW1.1
23 Rounded-square wave data bursts
26 Rounded-square wave data bursts
31 BATT POS
36 U3 - SW1.3
38 U3 - OCMP1_A / AIN10 / PF4 Square wave data bursts, 0.2msec per bit
39 RED WIRE
40 Battery voltage Around 9VDC measured
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 Notes/Observations
1 +5VDC
2 Unknown 3V rounded square pulses, 2x per second, 2 different periods avg ~75msec?
3 +5VDC
4 Unknown 5V, 0.1msec pulse once per second
5 +5VDC
6 Unknown 5V, 0.1msec pulse once per second
7 +5VDC
8 Unknown 3V, 250msec pulse once per second

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

U15 - 92JK ZC5 (can't find much on this component)

92JK ZC5 chip noted as U15
U15 Pin Function Observations/Notes
1 GND
2 5VDC
3 Rounded square wave (maybe sawtooth) alternating between 2msec and 4msec, resting at +3VDC between bursts
4 Rounded square wave alternating between 3msec and 5msec, short periods of 0v, resting at +3VDC between bursts
5 Data. Square wave. 5V space, 0v mark? Pulses around 250msec per bit.
6 More rounded square wave bursts
7 5VDC
8 3.3VDC


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 Transmitter Circuit

The transmitter RF path contains a filter IC, pi matching network, broadband amplifier, and a few more output filter stages.

Schematic diagram



Relative Humidity Circuit

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

Modifications

Disable amplification

When testing, it's important not to transmit on unlicensed frequencies. Emissions can be eliminated by removing the RF amplifier from the chain and terminating the load at the antenna connection. The amplifier is an SOT-89 device just above the "-" terminal of B3. To access this RF chain, the shield housing may need to be temporarily removed. Also remove the bias feed resistor just below the "L104" marking. Then, remove the transmitter antenna from the "ANT1" connections. Use a 50 ohm resistor across the two terminals to provide a terminating load and eliminate any further transmission. Near-field reception is still possible after making these changes.