# Prototype EMWIN Receiver Station Design

###### And DLL User's Manual

This document describe NOAA's "prototype" software based receiver,
designed to support the DFSK modulation employed in the existing EMWIN-I
broadcasts as well as the new BPSK modulation that will be employed in
the next generation EMWIN-N broadcasts. The document consists of three
sections, 1. Prototype EMWIN Receiver System Description, 2.
Configuration Parameters for the NOAA provided executable software
modules, and 3. Prototype Receiver Setup. This document provides design
information that may be useful for developing relatively low cost EMWIN
receiver stations, especially those that can employ the NOAA provided
executable software or Data Link Libraries (DLL's). This document may
also serve as a basis for a users guide for receivers that incorporate
these DLL's .

Subsequent versions of this draft document will be provided based on
user and vendor feedback.

# 1. Prototype EMWIN Receiver System Description

![](media/image1.wmf)

Figure 1 EMWIN Receive Station Overview

######## EMWIN Prototype Receiver Station Specifications

The EMWIN Receive Station described herein was developed as a prototype
dual purpose station to satisfy both existing (i.e., GOES I-M) and
future (i.e., GOES N-P) broadcast requirements and is designed to
facilitate transition from EMWIN-I to EMWIN-N. The user data format,
content and basic capacity will not change appreciably between the
existing and new broadcasts. The major EMWIN receiver characteristics
for the existing and new systems (i.e. EMWIN-I and EMWIN-N) are
summarized in the Table 1.

**Table 1, Major EMWIN Receiver Characteristics**

  -------------------- ------------ --------------- ------------------------- --
  **Characteristic**   **EMWIN      **EMWIN N-P**   **Comment**               
                       I-M**                                                  

                                                                              

  **Receive            1690.725 MHz 1692.700 MHz    Dual frequency capability 
  Frequency**                                       will facilitate           
                                                    operational cutover       
                                                    during the transition     
                                                    phase                     

                                                                              

  **G/T**              -0.3 dB      -0.3 dB         Since this characteristic 
                                                    has not changed, the      
                                                    existing antenna, and     
                                                    perhaps the LNA, should   
                                                    be reusable               

                                                                              

  **Modulation**       DFSK         BPSK            Dual modulation           
                                                    capability will           
                                                    facilitate operational    
                                                    cutover during the        
                                                    transition phase          

                                                                              

  **Coding**           None         R-S, ½ Rate     Conforms to CCSDS         
                                    Convolutional                             

                                                                              
  -------------------- ------------ --------------- ------------------------- --

As is shown in Figure 1, the prototype receiver employs two additional
receiver hardware components which are not typically part of currently
deployed EMWIN solutions. The first component is the UHF/VHF frequency
adapter, which is necessary to translate the signal into an appropriate
interface for the second component, an analogue to digital (A/D)
converter. The prototype system has a 137.25 MHz interface on the front
end of the UHF/VHF frequency adapter, and an M-Audio 2496 professional
grade sound card to perform the A/D conversion. The UHF/VHF frequency
adapter currently has no commercial equivalent source.

The EMWIN receiver will perform the typical RF and IF functions as well
as the demodulation and data recovery functions required for reception
and display of the satellite broadcast data. The prototype software
based receiver employs software to perform the demodulation and data
recovery (i.e. decoding) function. The software or Data Link Libraries
(DLL's) are executables designed to run on a conventional PC running
Windows NT/2000/XP (e.g., Pentium IV) leaving sufficient capacity to run
additional EMWIN display and data management software. The DLL's should
also run under Windows 95/98/Me in a debug or console mode. The G/T of
the antenna should be at least -0.3 dB which is the same requirement for
both EMWIN-I and EMWIN-N. The low noise amplifier (LNA) has a noise
figure of less then 2 dB. The LNA RF output down converts the RF
frequency to an IF frequency of 137.25 MHz. The VHF EMWIN IF converter
amplifies the IF signal sufficiently to interface with the Analog to
Digital (A/D) converter which was designed to have nominal output signal
of -10 dBm. All of the down conversion parts employ oscillators which
have a frequency stability of at least 5 ppm. The A/D converter converts
the analog IF data to a digital format. This converter has a pass band
of \> 40 KHz, a sampling rate greater than 96 kilo-symbols per second
(KSPS) and a bits/sample rate of 16.

The prototype system uses a 1.2 Meter Andersen dish with a Quorum down
converter to 137 MHz. The output of the Quorum down converter feeds into
a UHF/VHF frequency adapter designed to amplify, filter, and frequency
translate the signal to be compatible with a commercially available
sound card. The sound card is an M-Audio 2496 sound card which is
capable of sampling at 96 KSPS and has an analog bandwidth of
approximately 48 KHz. It is important that the sound card have a
frequency response near 48 KHz, since the new BPSK signal will occupy a
bandwidth of over 22 KHz. The additional frequency allowances are
necessary to accommodate frequency tolerances within the down converter
signal chain. Many sound cards advertising a 96 KSPS sample rate may not
have a frequency response covering the full 48 KHz, and must be verified
if a different sound card is to be used instead of the one specified
here.

####### Data Link Library (DLL) Input Summary

A/D Converter (e.g., sound card)

> Sample rate of \> 96 Ksps
>
> 16 bits per sample
>
> TCP/IP socket output
>
> 48 KHz bandwidth

**Data Link Library (DLL) Output Summary**

FSK:

> Output Data (demodulated FSK bitstream)
>
> TCP/IP Socket (data only, no start/stop bits)
>
> RS-232 Serial Output (V.35, 9600 baud, 8, N, 1)
>
> Effective Data Rate: 7680 bps

BPSK:

> Output Data (demodulated, CCSDS processed bitstream)
>
> CCSDS Error Detection and Correction
>
> CCSDS CADU, VCDU, BPDU Wrapper removed
>
> TCP/IP Socket (data only, no encapsulation)
>
> RS-232 Serial Output (V.35, 19200 baud, 8, N, 1, gaps inserted)
>
> Effective Data Rate: 9537 bps

**EMWIN-N Coding and Data Format**

The Convolution Code follows the CCSDS recommendation and has been
selected to be the same as the LRIT broadcast. The code parameters are:
Rate = ½, Constraint Length = 7, no G2 Symbol Inversion. The Interleave
Depth follows the CCSDS recommendation and has been selected to be the
same as the LRIT broadcast. The Interleave is depth is 4. The
Reed-Solomon Code Descriptors and Symbol Size Code follow the CCSDS
recommendation and have been selected to be the same as the LRIT
broadcast. The CCSDS Reed-Solomon (255, 223) corrects 16 symbol errors
per interleave. There are 255 total Bytes per interleave (prior to
virtual fill), 223 input Bytes (prior to coding) per interleave, and 32
Reed-Solomon check symbols per interleave. The CADU contains 8192 bits
(including 32 bits ASM and 1024 Reed-Solomon check symbols); 4
interleaves with 892 data and 128 check symbols.

# 2. Configuration Parameters

## Common Parameters:

The following property sheets show the available options for both
EMWIN-I and EMWIN-N services. The data source service controls the
service which controls the input from the A/D converter, and pipes the
data across a sockets interface. The Data Source normally will run as a
service in the background of windows and will automatically start up
when windows is booted. The only items to note is the status of the data
source service as indicated by the icon on the control panel, which in
the included picture shows that the service is not running but is
installed. The only item which will normally be configured on this
screen is the TCP port number, which will be initially set to 5021.

![](media/image2.png){width="2.375in" height="3.4270833333333335in"}

The next screen shows the demodulator service settings, which controls
the included demodulator service. After installation, this screen will
show the status of the demodulator service, which when operating
normally will show a smiley face. The normal user configurable items
will be the IP address of the data source server, and the IP port number
(which needs to match the port number for the data source server), the
signal format (either 0-FSK or 1-BPSK), and the serial port number. The
serial port number is used to output the decoded bits in a format
compatible with current generations of EMWIN software. Alternatively an
output to a TCP connection is also possible, which is specified by the
outbound IP address.

### ![](media/image3.png){width="2.370833333333333in" height="3.425in"}

#### FSK Control Settings

![](media/image4.png){width="2.370833333333333in" height="3.425in"}
![](media/image5.png){width="2.370833333333333in" height="3.425in"}

##### Sample Rate

The front end sample rate needs to be set to the nominal A/D sample
rate. Under normal circumstances, the A/D sample rate will be 96 KHz for
a sound card solution. If the parameter is different, then it needs to
be set accordingly. It is stressed that the minimum sample rate needs to
be high enough to capture the entire bandwidth of the full signal. For
normal circumstances, the minimum A/D needs to be set at 96 KHz or
higher. The units of this parameter are in hertz.

##### Signal Present Threshold

This setting determines the threshold which is used to indicate whether
a valid signal is being presented to the demodulator. The parameter is
specified in terms of full scale voltage. The default setting is 0.002
or 0.2 % of full scale (voltage), or -54 dB from full scale.

##### Side Lobe Ratio

The side lobe ratio setting is used to determine whether or not the
demodulator appears to be tuned to a modulation side-lobe instead of the
real signal. The side lobe detector compares the RMS voltage presented
at the front end of the receiver, to the RMS voltage at the backend of
the low and high side "tuners" (essentially matched filters for the 0
and 1 symbols if everything is ok). If the observed ratio is not at
least as high as the value set by this parameter, then it will be
assumed that the signal is not locked onto the correct frequency, and
the receiver will be forced into acquisition mode. This parameter is
expressed as a linear ratio in the voltage domain.

##### AGC Gain

The AGC gain is the gain bandwidth setting. The value listed corresponds
to about a 10 Hz bandwidth at the given input sample rate, which is near
the minimum. If for some reason a users terminal experiences faster
fading (which is not expected for stationary installations), then this
parameter can be adjusted to a larger bandwidth setting to improve the
response of the receiver if required.

##### Decimation Ratio

The decimation ratio is used to decimate the input to be compatible with
the bandwidth of the signal. For sound card solutions, it is set to one.
The implementation of the decimation filter is not without computational
burden, and as a result, it is currently disabled in the version 1.0
release. If required to decimate the front end samples, it can be
enabled for users wishing to sample at a higher frequency.

##### Tuner Frequency

This parameters specifies the initial tuner frequency, and represents
the frequency as seen by the A/D converter. The nominal center frequency
has been designed for approximately 25 KHz, which is in the center of
the pass band of the software receiver using the illustrated sound card.
This parameter normally should be set to a value which is near the
observed frequency to speed signal acquisition time. It is also used as
the tuner frequency set point if one disables the automatic carrier
tracker function.

#### 

#### FSK Symbol Settings

##### FSK Delta F

This setting determines the FSK symbol frequency spacing in Hertz. In
the example, the FSK symbols are spaced approximately +\\- 3500 Hz for
the 9600 baud EMWIN downlink.

##### Low Filter Bank

The low filter bank controls the low frequency filter bank setting for
the low frequency symbol. Valid numbers range from 0 to 19, which
correspond to approximate bandwidths of {4800, 6240, 7200 , 8160, 9600,
12000, 14400, 16800, 19200, 21600, 24000, 26400, 28800, 31200, 33600,
36000, 38400, 40800, 45600}.

##### 

##### High Filter Bank

The high filter bank settings are identical to the low filter bank
settings, except they apply to the high side symbol.

##### Enable LPF

This enables or disables the filtering function for the low and high
side filter banks. This setting needs to be enabled for normal
operations, and should only be used for debugging purposes.

#### Carrier Track Settings

##### Enable Carrier Tracker

This enables or disables the carrier track loop.

##### Decimation Ratio

This reduces the number of samples processed by the carrier tracker
loop.

##### Signal Present threshold

This value used to determine whether a signal is present in the mark and
space signals relative to the input level.

##### Enable Low Pass Filter

This enables a low pass filter to eliminate unwanted noise into the
carrier tracker.

##### Low Pass Filter Bank

This sets the bandwidth of the low pass filter.

##### Acquisition Lead and Lag Gain Settings

This determines the effective carrier tracker bandwidth during
acquisition. Higher numbers increase the carrier tracker bandwidth, and
represent parameters in a lead-lag 2^nd^ order loop. Normally, the ratio
between the two should be kept near constant.

##### Track Lead and Lag Gain Settings

This is similar to the previous setting, except these are used when the
receiver determines that the signal is in a tracking state.

##### Frequency Minimum and Maximum Settings

This sets the minimum and maximum frequency (in A/D space) which the
receiver will search for the signal.

##### Frequency Sweep Settings

This determines how fast the signal will sweep across the pass band
frequency when in acquisition mode.

### BPSK Control Settings

![](media/image6.png){width="2.370833333333333in" height="3.425in"}
![](media/image7.png){width="2.370833333333333in" height="3.425in"}

The following icons are used to display the status of both the Data
Source and Demodulator service status. The meanings are as follows:
service running normally, service either starting up or shutting down,
service not running and service not installed.

![](media/image8.png){width="0.3333333333333333in"
height="0.3333333333333333in"}
![](media/image9.png){width="0.3333333333333333in"
height="0.3333333333333333in"}
![](media/image10.png){width="0.3333333333333333in"
height="0.3333333333333333in"}
![](media/image11.png){width="0.3333333333333333in"
height="0.3333333333333333in"}

# 

# 3. Prototype Receiver System Setup

1.  Connect the signal from the 137 MHz downconverter into the input of
    the VHF frequency converter box.

2.  Connect the output of the UHF frequency converter box into the line
    input of the M-Audio sound card.

3.  Verify that the sound card has a valid signal. Since the signal will
    be ingested by the sound card, first determine that the signal is
    present by looking at the signal at the soundcard input. For the
    M-Audio 2496 installations, the control panel applet which comes
    with the sound card displays the current input line level, which is
    where the signal will appear. If there is a signal present, then the
    display can be used as a signal strength meter to help with setting
    up the antenna. A more capable program
    <http://audacity.sourceforge.net/windows.php> is able to record and
    display the "spectrum" of the input signal, which will verify that
    the signal appears to be centered in frequency.

4.  The demonstration system used required 2 serial ports to ingest the
    signal, as well as a RS-232 loop back cable. Connect the loop back
    cable from serial port 1 to serial port 2 using a DB9 to DB9
    connector. The reason that this was required was to enable the
    software which was written with serial port support to be able to
    work without upgrades or modifications.

5.  The default settings for the software demodulator are contained in
    the EMWINSettings.reg file distributed as part of the installation
    package. Double click on this file (must have administrator
    privileges) to reinstall the default settings into the registry.
    Normally, only the serial port number will need to be reconfigured.
    The application is configured through the supplied control panel
    applet.

6.  Restart the machine or alternatively restart the two services making
    up the demodulator.

7.  The next step is to be certain that the parameters are setup
    correctly. Use the control panel applet and this document as a
    guide. These settings contained here will be set as the defaults for
    initial installs.

#