All Weather Inc 20981 User manual

All Weather Inc. • 1065 National Drive • Sacramento, CA 95834 • USA • 800.824.5873 • www.allweatherinc.com
Model20981
UHFDataRadio
User’s
Manual
Rev. A

Copyright ©2020, All Weather, Inc.
All Rights Reserved. The information contained herein is proprietary and is provided solely for the purpose
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and the All Weather, Inc. logo are trademarks of All Weather, Inc.
Disclaimer
The information and specifications described in this manual are subject to change without notice.
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Model 20981 UHF Data Radio User’s Manual
Revision History
Revision
Date
Summary of Changes
A
2020 Feb 15
Initial release.

Model 20981 UHF Data Radio User’s Manual
TABLE OF CONTENTS
OVERVIEW.........................................................................................................................1
1.1 Installation Kits...........................................................................................................................1
1.2 FCC Regulations.........................................................................................................................1
1.2.1 Licensing.............................................................................................................................1
1.2.2 Equipment Authorization (Certification)............................................................................1
1.2.3 Radio Frequency Exposure.................................................................................................2
I/O CONNECTOR AND LED INDICATORS........................................................................3
2.1 I/O Connector .............................................................................................................................3
2.1.1 Pinout Description ..............................................................................................................3
2.2 LED indicators............................................................................................................................5
OPERATION.......................................................................................................................6
3.1 Channel Selection.......................................................................................................................6
3.2 Power Supply Voltage................................................................................................................6
3.3 Current Drain vs Supply Voltage ...............................................................................................6
3.4 Duty Cycle/Key-Down Limitations............................................................................................7
INSTALLATION...................................................................................................................8
PROGRAMMING THE DATA RADIO .................................................................................9
5.1 Frequency Tab..........................................................................................................................10
5.2 Other Tabs ................................................................................................................................10
5.2.1 Buttons..............................................................................................................................10
5.2.2 General Tab.......................................................................................................................11
5.2.3 Modem Page .....................................................................................................................12
5.3 Analog Tab ...............................................................................................................................14
5.4 Summary Tab............................................................................................................................15
5.5 Restore EE Tab.........................................................................................................................15
AWOS INSTALLATION.....................................................................................................17
6.1 DCP Installation........................................................................................................................17
6.2 CDP Installation........................................................................................................................17
MAINTENANCE................................................................................................................18
7.1 AWOS Maintenance Procedures..............................................................................................18
7.1.1 Monthly Maintenance.......................................................................................................18
7.1.2 Triannual Maintenance .....................................................................................................19
7.1.3 Annual Maintenance.........................................................................................................19
SPECIFICATIONS ............................................................................................................21
WARRANTY......................................................................................................................23

Model 20981 UHF Data Radio User’s Manual
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1. OVERVIEW
The Model 20981 UHF Data Radio is an integrated modem and radio that provides digital data
transmission at data rates of 9600 bps in a 12.5 kHz channel over a frequency range of 450–
470 MHz. The user data interface is a serial port through a 15-pin D connector, and is configured
for RS-232 signal levels. The Data Radio comes in a small, compact package that is easy to
integrate into new systems or retrofit into existing systems.
Transmit and receive LEDs provide the operational status of the Data Radio.
The antenna interface to the Data Radio is through a standard 50 Ω female BNC connector. A
variety of antennas can be used.
1.1 INSTALLATION KITS
Kits have been prepared to allow the Model 20981 UHF Data Radio to be installed in an AWOS
3000 CDP, a DCP, or as a retrofit to a previous installation using other radio modems. The kits
provide the UHF Data Radio(s), attenuator, other hardware, and cables needed for the
installation.
Table 1. Model 20981 UHF Data Radio Installation Kits
Part Number
Description
M488306-01
AWOS 3000 CDP Installation Kit
M488678-00
Retrofit Kit to replace AWOS 3000 CDP and DCP radios
M488679-00
DCP Installation Kit
1.2 FCC REGULATIONS
1.2.1 Licensing
The FCC and regulatory authorities in other countries require that the radio owner/operator
obtain a station license for the radio before using the equipment to transmit, but do not require an
operating license or permit. The station licensee is responsible for proper operation and
maintenance of the radio equipment, and for ensuring that transmitter power, frequency, and
deviation are within the limits specified by the station license. This includes checking the
transmitter frequency and deviation periodically using appropriate methods.
1.2.2 Equipment Authorization (Certification)
FCC Approval had been granted for the Model 20981 UHF Data Radio in November, 2014.

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1.2.3 Radio Frequency Exposure
The FCC, with its action in General Docket 79-144, March 13, 1985, adopted a safety standard
for human exposure to radio frequency electromagnetic energy emitted by regulated equipment.
The Model 20981 UHF Data Radio has been evaluated for compliance with the maximum
exposure limits for RF energy at the maximum power rating of the unit. To ensure compliance
with the General Population/Uncontrolled maximum exposure limits, please ensure that all
persons will be at least 20.5 cm (8.1") away from the antenna.

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2. I/O CONNECTOR AND LED INDICATORS
2.1 I/O CONNECTOR
Table 2. I/O Connector Pinout
Pin
Name
Description
Comments
1
—
—
Not used
2
—
—
Not used
3
—
—
Not used
4
A/B
Input
Channel 1/2 or High/Low power
5
RSSI
Output
Analog Receive Signal Strength Indicator
6
Supply
Input
DC Power connects here to power unit
7
NC
Output
Receiver Alignment—DO NOT CONNECT
8
RD
Output
RS-232 data output from modem
9
TD
Input
RS-232 data input to the modem
10
CTS
Output
RS-232 clear to send output from modem
11
DSR
Output
RS-232 data set ready output from modem
12
—
—
Not used
13
CD
Output
Carrier detect
14
RTS
Input
RS-232 request to send input to modem
15
GND
System ground (power supply and signal)
2.1.1 Pinout Description
Pin 4 (A/B)
Depending on how it is programmed via the programming utility, Pin 4 can either be a Channel
A/Channel B selection pin or a High/Low transmit power selection pin. This pin has an internal
pullup resistor to +5 V and assumes a high (channel A or high power) state when left
unconnected.
Pin 5 (RSSI)
Pin 5 is an analog output whose amplitude is proportional to the signal strength of the received
signal. The voltage at this pin varies from about 1.6 VDC for a -130 dBm signal to about 4 VDC
for signals at or above -60 dBm.

Model 20981 UHF Data Radio User’s Manual
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Pin 6 (Supply)
Pin 6 is the positive power supply input for the modem.
Pin 7 (Receiver Alignment)
Pin 7 is the output pin of the modem IC’s input operational amplifier. It is used during alignment
to set the receiver gain and DC offset for proper modem IC receiver decoding. This pin must be
left unconnected.
Pin 8 (RD Receive Data)
RS-232 data to be received from the modem are available at Pin 8. The data are at normal
RS-232 levels and are transmitted from the modem to be received by the host computer or other
device connected to the modem.
Pin 9 (TD Transmit Data)
RS-232 data to be transmitted to the modem should be presented to Pin 9. The data should be at
normal RS-232 levels and are transmitted from the host computer or other device to the modem.
Pin 10 (CTS Clear to Send)
This RS-232 output pin is asserted by the modem as a response to an assertion of the RTS pin
when it is ready and able to receive data from the host computer or device.
Pin 11 (DSR Data Set Ready)
This RS-232 output pin is asserted by the modem when it is powered-up. It indicates that the
modem is actually connected, although not necessarily ready to receive data. The polarity (active
low/active high) is programmable via the programming utility.
Pin 13 (CD Carrier Detect)
Pin 13 is asserted by the modem when the receiver has detected a carrier. The RF level for CD
assertion is set via the programming utility. Note that the modem demodulation circuitry does
not actually use this signal to determine that a valid data packet has been received. The polarity
(active low/active high) is programmable via the programming utility
Pin 14 (RTS Request to Send)
This RS-232 input pin is asserted by the host computer or device to indicate that it has data to be
transmitted by the modem. If the modem is able to accept the data, the CTS pin will be asserted
in response.
Pin 15 (GND Ground)
The system ground common point and negative connection for the power supply and RS-232
signals.

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2.2 LED INDICATORS
The Model 20981 UHF Data Radio has two LEDs on the side of the unit, one green RX LED and
one red TX LED.
•The GREEN RX LED can be programmed to be illuminated under a variety of
conditions. The choices are:
oNever (Off)
oWhenever power is applied (Power On)
oWhen receiving, whether or not an actual signal is on the frequency
(RX Synthesizer Lock)
oWhen receiving and an actual data packet is being received (RX Data).
In typical applications, either RX Synthesizer Lock or RX Data is selected.
•The RED TX LED can be programmed to be illuminated when the modem is
transmitting, or to be never illuminated.

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3. OPERATION
3.1 CHANNEL SELECTION
The Model 20981 UHF Data Radio supports one channel if the A/B pin (pin 4) is programmed
for high/low power and two channels if the A/B pin is programmed as a channel select input.
Channel A is set when the A/B pin is activated and the A/B pin is in the logic high state, i.e.,
above 2.0 VDC or is left unconnected. (There is an internal pullup resistor on the A/B pin.)
Channel B is set when the A/B pin is activated and the A/B pin is in the logic low state, i.e.,
below 0.5 VDC. If the A/B pin is programmed for high/low power, channel A is always selected.
A change in the channel selection in receive will cause the receiver to operate on the new
channel. In transmit, however, the channel selection is only checked only at the beginning of a
transmission. Changes in channel during transmit will not change the transmit operating channel
of the unit until the unit is cycled from transmit to receive and back to transmit.
3.2 POWER SUPPLY VOLTAGE
The supply voltage can be at any voltage between 11 and 16 VDC. Since the module is powered
directly from this voltage, the supply should be “clean” and, preferably, regulated. The output
power will vary with supply voltage. Switching power supplies can be used, but exercise care so
that the output waveform is low noise. Also, the module antenna should never be placed near an
unshielded switching power supply.
3.3 CURRENT DRAIN VS SUPPLY VOLTAGE
The current drain of the module is a function of the supply voltage as shown in Table 3.
Table 3. Current Drain vs Supply Voltage
Supply Voltage
Current Drain
Receive Mode
11.0 V
100 mA
12.5 V
90 mA
16.0 V
75 mA
Transmit Mode
11.0 V
1.1 A
12.5 V
1.0 A
16.0 V
0.7 A

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3.4 DUTY CYCLE/KEY-DOWN LIMITATIONS
The major heat-generating component within the radio is the RF power amplifier, which has a
maximum temperature limit that should not be exceeded. In addition, the temperature within the
radio itself must be kept below the maximum temperature of the reference oscillator to ensure
that regulatory frequency stability limits are observed. As a result, limits on the average transmit
duty cycle and the maximum continuous transmitter-on time exist, and depend on the supply
voltage and the ambient temperature. These limits are summarized in Table 4 for operation in
still air.
Table 4. Transmitter Limits Based on Temperature
Ambient Temperature (°C)
Duty Cycle (%)
Key-Down Time (s)
25
30
45
50
5
10
The operation of the Model 20981 UHF Data Radio in All Weather Inc. AWOS systems will be
within these limits.
Blowing air across the unit and/or adding a heat sink to the rear of the unit where the PA module
is located can significantly improve the duty cycle/key-down times for other uses.

Model 20981 UHF Data Radio User’s Manual
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4. INSTALLATION
The Model 20981 UHF Data Radio has two connectors, a female BNC connector for the RF
(antenna) connection and a 15-pin D-subminiature for the data/programming interconnection.
Connect the BNC connector to a suitable antenna or RF dummy load or attenuator, depending on
the installation. If an antenna is connected, it should be placed at least 3 m (10 ft) away from the
radio itself to prevent RF interference. Also, any antenna must present a good 50 RF load (low
VSWR) at the operating frequency.
Note that a 1 dB attenuator must be used with All Weather Inc. AWOS systems.
The 15-pin connector is usually used with the M493135-00 programming cable, which provides
for DC power connections and a serial connection for programming and for the data to
transmitted and received. Figure 1 shows the wiring diagram for this cable.
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
D-SUB 15
D-SUB 9
WHT
RED
BLK
BLK
WHT 1
2
3
4
4-PIN PC
POWER
CONNECTOR
WHT
BLK
WHT
RED
GRN
GRN
Figure 1. M493135-00 Programming Cable Wiring Diagram

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5. PROGRAMMING THE DATA RADIO
Use the PCPS programming utility to configure and adjust the operating parameters of Model
20981 UHF Data Radio. Load the programming utility on a host computer. If the utility does not
install automatically, it can be started manually by running “Setup.exe”.
Connect the Data Radio to the host computer with the 9-pin connector (Figure 1). Connect the
power connector to a power supply that delivers 11–16 VDC. In programming mode, the current
required by the Data Radio is about 150 mA and the power supply should be capable of
supplying that current. Note that 2 to 3 A is typical for the transmit mode. It is possible to
transmit with the programming utility running, but the power supply must be able to supply the
necessary current and a suitable RF load must be provided on the BNC connector.
Once the Data Radio is connected to the host computer and a power supply is connected, open
the programming utility and turn the power supply on. The first screen is the “welcome” screen
shown below. Note that the voice parameters are used with the Model 20981 Data Radio.
The button at the upper right is the “Programmer Configuration” button and is used to set the
serial communications baud rate for communications between the programmer and the host
computer. It defaults to 38400 baud, but can be set to other common serial rates. If the host
computer baud rate is unknown, click the “Test Configuration” button to auto-detect the baud
rate. Click OK to confirm the choice of baud rate.
The “Read Radio” button is used to read the contents of the radio into the programmer so that the
current configuration of the radio can be observed and edited.

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5.1 FREQUENCY TAB
Click the “Read Radio”button. The Frequency tab will open.
This page shows the frequencies programmed into the Data Radio. Depending on how the A/B
pin is programmed, either one or two pairs of frequencies will be displayed. Frequencies can be
programmed into the device by clicking on the appropriate field and typing in the desired
frequencies. The frequencies must be within the operating range of the radio and must be
divisible by the synthesizer step size. In addition, there are five other tabs and five buttons that
can be selected. These are summarized below.
5.2 OTHER TABS
The tabs show up on all the pages. Clicking on a tab moves one to that page. Frequency, as
explained above, allows the operating frequencies to be viewed and/or changed.
Other tabs are shown below and their contents will be discussed in detail.
•General shows the general operating parameters of the Data Radio.
•Modem shows the parameters such as protocol.
•Analog shows the parameters of the analog/voice path.
•Summary shows all of the Data Radio parameters on one page.
•Restore EE-allows the configuration of the programmed Data Radio to be saved.
5.2.1 Buttons
There are five buttons that show up on all the pages.
•Receiving is a software (programmer) PTT selection. Selecting this button will put the
Data Radio in transmit mode. Selecting this button again will return the radio back to
receive.

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•Monitor is a software (programmer) Monitor selection. Selecting this button will unmute
the analog/voice receiving path of the Data Radio. Selecting this button again will return
the radio back to normal squelched operation. Note that if unsquelched operation is
selected on the Analog page, this button will have no effect.
•Clone Radio allows the Data Radio parameters to be copied into another radio.
•Update Radio loads the programmer’s parameters into the Data Radio. Note that
changes made via the programmer are not saved permanently into the Data Radio until
this button is selected. The radio’s behavior will change as changes are made via the
programmer, but will be lost on power-down unless, and until, this selection is made.
•Read Radio reads the Data Radio’s parameters into the programmer to view and edit.
5.2.2 General Tab
The General tab is shown below.
•A/B Input One or Two Channel-Determines the function of the A/B pin. This pin can
be used to control the power selection, high or low, for one channel, Channel A, or it can
be used to choose between Channel A and Channel B, in which case the output power is
high for both.
•Comm Port Baud Rate determines the baud rate for communications between the data
device and the Data Radio. This number should match that shown on the Programmer
Configuration screen.
Note: This is the only selection that saves the current memory configuration to permanent
memory.
•Test Pin Input Logic Level (PTT) determines the polarity of the test pin. The test pin is
used to put the radio in transmit in analog/voice mode or to send test patterns in modem
mode. This pin has an internal pullup resistor and thus, assumes a logic high state when
not connected. Therefore, active low is the normal, default setting.

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•Red LED determines the behavior of the red LED indicator. The choices are that it can
be set to never be illuminated or illuminated when the radio is transmitting.
•CD Output Logic Level determines the polarity of the CD (Carrier Detect) output pin.
•Green LED determines the behavior of the green LED indicator. The choices are for it to
never be illuminated (off), be illuminated whenever the radio is powered (Power On),
when the receiver is locked and receiving (RX Synthesizer Lock), or data/analog
information is being received (RX Data). In the latter mode, the indicator would come on
whenever one of two conditions is met, the squelch level (carrier detect level) is
exceeded, even when Squelch is never muted, or when the receive data has detected a
valid data stream.
Note: The Power On setting disables the Red Led indicator.
•TX Low Power/TX High Power allows setting the RF output power for the two states of
the low/high power pin. The low-power selection corresponds to the low logic level of
the pin while the high-power selection corresponds to the high logic level. Note that the
high-power selection does not necessarily have to be greater than the low-power
selection. Each is independent of the other and only corresponds to a state of the power
select pin.
•Per Channel Values summarizes the high and low power settings for the channels used
by the Data Radio.
5.2.3 Modem Page
The Modem tab allows the selection of the parameters of the Data Radio mode operation.
•Modem Protocol selects the over-the-air protocol. Although there are three choices, only
the last one applies to the Model 20981 Data Radio.
oProtocol 2.00 (Legacy) is a very robust packet protocol useful for large data
blocks, but not for fast streaming or fast polling.

Model 20981 UHF Data Radio User’s Manual
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•Test Patterns (via Test Pin) Selecting any of the selections in this box will cause a test
pattern to be transmitted when the Test Pin (PTT) is active. If no selection is made,
activating the Test Pin will cause the Data Radio to transmit in analog/voice mode. The
choices are:
oBit Error Rate (BER) A pin pattern is generated that allows for the computation
of the bit error rate, setting deviation, or observing an eye pattern. The pattern is
511 symbols long with no synchronization symbols and repeats continually. It is a
maximal length pattern with feedback taps at the 5- and 9-bit positions.
oSend Test Pattern A packet that transmits over and over with a constant data
structure. This pattern can be used to test the system in the low latency and
streaming modes.
oSquare Wave Generator transmits a 400 Hz square wave used to set the
deviation and modulation balance during alignment or to hear the transmitted
400 Hz tone on a receiver or radio modem in analog/voice mode.
oTX Carrier Mode is an unmodulated carrier is transmitted.
•Protocol 2.00 The items is this box select the identification parameters used in the legacy
2.00 protocol.
•Source Station ID sets the address of the Data Radio itself. It is made up of 4 parts, from
most general to most specific: System ID, Group ID, Unit ID, and Sub-unit ID.
•Default Destination ID sets the destination ID of the intended recipient.
•Protocol Mask determines how close a mask must exist between the Data Radio’s ID
and the destination ID in the message before accepting and outputting to the host the
message.
A “1”for any location in the mask requires a perfect match, while a “0”means a “don’t
care”situation. This is useful for “broadcast”, i.e., one unit transmitting to more than one
unit situation. Note: In broadcast applications, the “Acknowledgement after TX”
selection should NOT be selected to prevent multiple units from responding and
interfering with each other. See “Configuration”.
•Configuration
oAcknowledgement required after transmit When checked, the Data Radio will
require an acknowledgement after each transmission or the transmission will be
repeated.
oMessage Retry Limit and Timeout Time The amount of time in ms that the
Data Radio will wait for an acknowledgement and the number of times it will
repeat a message can be set in the Message Retry Limits box and the Time Out
Time boxes.
oDead Carrier before Symbol Sync The amount of time in ms that an
unmodulated carrier will exist before the beginning of the symbol sync pattern.

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oPartial Packet Timeout The amount of time in ms of no data from the data
device that must exist before a packet is formed and transmitted.
5.3 ANALOG TAB
The Analog tab allows selection of the analog/voice mode parameters.
•TX pre-emphasis selects whether the external audio signal is pre-emphasized, i.e., has
its high-frequency audio content boosted or whether the signal is sent with a flat audio
response. Voice signals typically use pre-emphasis.
•RX de-emphasis selects whether the external audio output signal is de-emphasized i.e.
had its high-frequency content attenuated or whether the signal is outputted with a flat
frequency response. Pre-emphasis and de-emphasis are normally used together.
•Busy Channel TX Lockout allows a transmission to be inhibited if there is activity on
the receive frequency. This would normally be used when the transmitter and receiver
operate on the same frequency, and is used to avoid interference to a transmission already
in progress. The presence of activity of the channel is determined by signals that exceed
the Carrier Detect On setting (see below).
•CD Output Level sets the logic level of the Carrier Detect Output pin.
•Squelch Enable selects whether signals below the Carrier Detect Off level will be muted
(squelched) or whether all signals are allowed to pass to the audio output pins.
•TX Timeout Timer selects whether the transmitter in limited in the maximum time that
it is allowed to transmit continuously and how long that time would be. This is designed
to avoid overheating the transmitter when the Test (PTT) pin is taken active for a long
time.
•Aux Out (RX) Gain sets the audio output level for the audio output pins.

Model 20981 UHF Data Radio User’s Manual
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•Aux In (TX) Gain sets the gain, not the maximum deviation, for signals at the audio
input pins.
•Carrier Detect On (dBm) sets the RF signal level in dBm such that the carrier detect pin
will go active and the output audio, if squelch is selected, will go unmute.
•Carrier Detect Off (dBm) sets the RF signal level in dBm such that the carrier detect pin
will go inactive and the output audio, if squelch is selected, will be muted.
Note: The Carrier Detect On level must be set to be higher (less negative) than the
Carrier Detect Off level.
5.4 SUMMARY TAB
The Summary tab summarizes all the selections from the previous pages.
5.5 RESTORE EE TAB
This tab is used to restore saved configurations into other Data Radios. To save a configuration
file, select File, Save EE to file, or when the programming utility is closed, select the option to
save the file. All parameters are saved. When restored, only select parameters are restored
depending on the option selected.
Check one of the three boxes to save the current configuration. Besides not saving a
configuration by not checking any option, there are three options.
1. Saving all parameters
2. Saving all except the squelch and RF power level (useful if the Data radio already has
power and squelch settings that are to be retained)
3. Convert older DTXM-X54 series products to the configuration of the Series II modems
(not used for the Model 20981 UHF Data Radio)