Emergency Managers Weather Information Network Frequently Asked Questions (FAQ)
The National Weather Service EMWIN team has received many comments and questions about the specifications, the prototype design and associated software which were recently added to its EMWIN website. These updates were all related to transition to the GOES-N satellite at such time as it becomes operational. Receiver system designs which are capable of making this transition are called “EMWIN-N” receivers as distinct from those receivers currently in operation with the GOES-I satellite generation, referred to here as “EMWIN-I” receivers. Here are answers to the most “Frequently Asked Questions” which we received.
1. Do manufacturers need to use the EMWIN-N software-based prototype design as described on the EMWIN website?
No. Manufacturers are free to design any alternative system that will work in compliance with the signal specifications. The EMWIN-N receiver prototype was designed primarily as a “proof of concept” to demonstrate that a receiver for the EMWIN-N signal could be constructed. The software defined radio concept has, however, become an important technology in the past several years because of its inherent flexibility in making future changes.
2. Is it necessary to use a sound card to ingest the EMWIN signal?
No. A sound card was used in the prototype to function only as an analog-to-digital converter. It was proposed simply because it is readily available, of relatively low cost, and will plug into a PC that is needed to run the software that will process the digital output from the sound card. A potential manufacture may of course elect to use other design approaches to avoid the use of the sound card. Some older sound cards will not work. However, at least 5 types were tested by NESDIS and 4 of the 5 were found to be reliable. Refer page 18 of the 19.2 specification.
3. What capabilities does a sound card need to have in order to work with the prototype demod/decode (DLL) software?
Any reasonable quality dual channel (stereo) sound card capable of a 48 KHz sample rate should work. A line-in connector is needed for connection to the IF adapter.
4. What is the purpose of the IF adapter?
The IF adapter is needed to convert the output from the existing
down converter (about 137 MHz on most systems) to the frequency
needed for the input to the sound card. For example, if the signal
out of the existing down converter is at a center frequency 137.725
MHz, the IF adapter needs to include a mixer
Note: If the existing down converter output frequency is 137.725 MHz, the output frequency of the EMWIN signal from the GOES N satellite will be 139.700 MHz. Therefore the L.O. in the IF adapter would need to be changed to 139.675 MHz to maintain the same input frequency range into the sound card.
5. Is it possible to construct a hardware only
solution that will provide
Yes. Other approaches are also possible.
6. Will a reference design for the modulator with FEC coding be made available to end users?
Yes. A description of the input processor (which will provide the coding, scrambling, and framing) and the modulator is included as part of the EMWIN-N specification.
7. Is the EMWIN-N specification and demodulation/decoding software free to be used by system designers?
8. Will the EMWIN-N prototype demodulate and decode both the current and future EMWIN signal?
Yes, with a crystal change. New or adapted EMWIN receivers, regardless of their design should have such a feature such as this to enable an easier transition as soon as the GOES-N satellite is placed into operational service.
9. Are manufacturers available for the Intermediate Frequency (IF) Adaptor schematic shown on the EMWIN website?
No, not yet. The prototype was only developed as a “proof of concept” design. Manufacturers may be able to develop a lower cost or more efficient design to accomplish the same purpose.
10. What about grants for local emergency managers to upgrade to EMWIN-N?
The NWS EMWIN team has been seeking grants to ease the transition for local government emergency managers in economically deprived areas, but thus far without success. We will persist in these efforts, however, and encourage you to also explore any possibilities of procuring state or other local grants.
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National Oceanic and Atmospheric Administration
National Weather Service
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Page Author: EMWIN Team
Web site owner: NWS/OPS17
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