EAS Decoding for fun using the TFT EAS911 ENDEC

by on Jul.25, 2023, under Hardware, RF and Radio

EAS Emergency Alert System logo credit FCC / WikiMediia Commons

The Emergency Alert System (EAS) is a US Nationwide alerting platform that uses a combination of terrestrial radio and television broadcasters to get an urgent message out to as many people as possible. In this article, we’ll be setting up the TFT EAS-911 ENDEC so we can receive these messages without being dependent on cellular service or Internet access.

So, what is EAS anyway?

The entire purpose of the Nationwide EAS system is to alert people to a potential emergency event (be it weather related, civil emergency, missing child, etc…) . While most people are just familiar with the often ill-timed tests that assault our ears with blasts of noise or the 3AM Amber Alert that wakes you up from that dream with the scantily clad beach babes, the underlying purpose of the EAS system is incredibly important.

The Emergency Alert System uses message encoding to control propagation of messages to indicate the relevant areas covered by just such an alert. For example, if there’s a tornado warning in Smith County, you don’t want to receive that in Bexar County as it’s not relevant. For those not familiar with Texas counties, Smith County is in the north east region of the state, while Bexar County is Central Texas.

Message Syntax and SAME Encoding

The EAS message syntax is fairly simple. It consists of three message headers, the attention tone, a spoken message, and finally three ending footer messages. The header and the footer are broadcast three times to ensure accurate reception of the message data contained in the headers as there’s no checksumming in the data stream. The header contains metadata about the alert, such as the station origin, the message type, a date/time stamp of the original transmission, and a SAME header. The SAME (Single Area Message Encoding) header is a way of being able to define the ‘effective area’ for an EAS message. This mechanism prevents a message for California from being rebroadcast in Florida for example.

Differences between AM/FM EAS and Wxband EAS

The biggest difference between the three sources is the attention tone used. All three use the SAME encoding and data protocol, but the attention tone between the SAME data and the voice announcement is different. The Weatherband EAS uses a 1050Hz tone while the AM/FM EAS (commercial radio) uses a two tones at 853Hz and 960Hz played at the same time. The difference in tones (and the intentional harshness of them) will help you be able to identify the EAS type based on the attention tone.

Which finally brings us to the ENDEC.

The EAS ENDEC (Encoder/Decoder) is designed to listen for EAS alerts, decode them, then retransmit them automatically without requiring operator intervention. It receives the EAS message, stores it locally in cache, then retransmits it using the configured station ID as its point of origin. In a Broadcast TV or Radio station, the ENDEC would be connected to the audio transmitter so that it could relay the message. In a TV station, additional equipment (like a character generator and video generator) would generate a full screen video image with the EAS message. When an EAS message is received by the ENDEC, the ENDEC could then autonomously cut in to the transmitter feed (audio/video/both) and could then retransmit the alert.

So, why are we doing this?

As everything moves from terrestrial radio and television to streaming options, reception of EAS messages has been problematic. Streaming services don’t often forward EAS messages or do so inaccurately leading to messages intended for one region being received in another. Cellphones get inundated with Amber Alerts for cities and states that are nowhere near the user and fire off at the worst possible time. In a quick poll of my friends, I didn’t find anyone that had Emergency messages enabled on their cellphones because of the annoyance of the false alarms which is the exact opposite effect you’d want for an emergency alert system. At my house, we wanted to be able to get EAS messages that are relevant for our location without being inundated with extraneous alerts and we didn’t want to have to rely on subscription services to get them.

For this task, I’ll be using the TFT EAS911 ENDEC I got off of Ebay for $80 shipped and three common radios (Thanks Amazon!) to listen to the three Primary Entry Point (PEP) radio stations in my area. EAS Alerts will result in a printed record I can retain or review. In a later addition, I can use a strobe light connected to the ALERT relay that will flash when an EAS message is being received by one of the radio sources.

And yes, while an emergency weather radio that receives Weather band EAS alerts exist, these have their own flaws. They only monitor one station, there’s no redundancy, and there’s no historical record for older alerts. Plus, it’s not as interesting or fun.


The EAS-911 ENDEC from TFT (a now defunct company) has four source inputs that are connected to common radios tuned to specific stations. When it hears the EAS message tones, it immediately receives and decodes the alert, then starts printing the message on the builtin printer. My unit came with a voice recorder module which also records the audio message so I can listen to the message again before discarding it. Since there’s no transmitter, all this does is decode the message and stores it for playback. The audio output connections are all unpopulated, so while this does have the capability to retransmit, without an actual transmitter in place and connected, all it’s going to do is receive and log which is what we want.

The Radio sources

Most common EAS implementations require three sources, an FM radio source, an AM radio source, and a Weatherband radio source as determined by the FCC and the state’s emergency action center. For Texas, this information was located at the Texas Association of Broadcasters website which was a quick Google search away. On the site, I found my area and the three listed PEP stations.

While I had tried initially to procure a triple-radio system that would fit in my rack, I realized quickly that this was an unattainable goal unless I wanted to spend 12x the cost of the ENDEC to get three radios. TFT did build a companion to the EAS-911 (the EAS-930A) however these are extremely rare and searching was fruitless for this device. Instead, I opted to use these AM/FM/WB radios to much success and at a much cheaper price than the 1U triple radio system.

The three radio sources attach to the back of the ENDEC via some three pin 5.5MM Phoenix connectors. A few 1/8 mono headset jack cables and I’ve got everything for the three sources. I procured some printer ribbon from Amazon, (EPSON ERC-09 B) and some standard paper receipt rolls (no thermal paper!) and I am ready for setup. In retrospect, the receipt paper rolls above are too large, you’ll have to take the rolls and re-roll them into smaller rolls to fit in the chassis.

Tuning and configuration

There’s only a few parameters that need to be set to be able to receive your area’s EAS messages. You need to set the system’s date and time, the SAME area ID (your county usually), and what messages to receive. For the first few weeks or so, I recommend receiving ALL messages just to test the operation of the ENDEC and then once you’ve received at least one alert on each channel/receiver, turn off the required weekly test (RWT) message type. The TFT manual will describe how to navigate the menu system and how to set up the various options (otherwise this will be a much longer post!)

The manual for the EAS-911 can be downloaded from here: https://www.steampoweredradio.com/manuals/tftm.html

Extra Stuff

After running the ENDEC for a while, it became apparent that the noise it produces is a bit rude but I still wanted to be able to be notified when an EAS message is being received. Fortunately, the ENDEC is designed for this and has a hardware option to turn on an indicator when an EAS message is being received. Using the ‘Alert Relay’ contacts, we can turn on a small light (or in my case, a strobe light) when an EAS message is being received. At some point in the future, I’ll wire this up to a strobe light that will go off when an EAS is being received so I’ll know that a message is being received.

All set up!

I’ve been running my ENDEC for about a month now and I’ve received a lot of alerts. While most of them are test notifications that I need to turn off, I have received some interesting alerts that weren’t just test messages. I received a few severe storm warnings, a tornado warning, and a civil emergency (This was in relation to an emergency power failure incident that required a significant number of people to go without power for a few hours).

TFT EAS 911 ENDEC on bottom of photo in a server rack with the three radio sources on top. Each radio source is tagged with a channel number and type (AM/FM/WX).

Final Thoughts

When I had started down this rabbithole, I was originally trying to get ahold of a SAGE ENDEC, which is a far more modern device. The networking capabilities and various other features made it an attractive unit however it also made it quite expensive. According to eBay, the SAGE units are selling at about $2000USD and the TFT ENDEC was on orders of magnitude cheaper even with the radios. I’ll keep scouring the Internet in the off chance I get lucky and can score one for cheap, but for now the TFT does exactly what I need it to do. The good news is that regardless of the ENDEC employed, they all essentially perform the same base functionality. Upgrading is always an option without having to completely re-tool your EAS reception equipment.

This was a fun and quick project that I was able to spin up for less than $200 and it’s already proven to be a useful tool. Last night we received an EAS for a pop-up storm and about ten minutes later the skies opened up with a fury. My phone had not received any alerts nor notifications from the handful of weather apps on it. While it wasn’t a truly “severe” weather event, it was significant enough that the National Weather Service pushed an alert out.

What about SDRs?

While a SDR could do this easily, the problem is that I didn’t want to dedicate the only SDR I have (HackRF) to such a task, nor did I have a comparable machine that could run the SDR. It might be possible with a dedicated machine however you’d end up with the same issue of the weatherband alert radios, only one source can be monitored at a time without spending a significant amount of money on SDRs, antennas, and other miscellany to get a working comparable system. I’m sure there’s at least a dozen different code projects that can use a SDR for tuning and reception of EAS messages, but I haven’t looked into them very deeply because of the hardware required.

All in all, this was a fun little project. I enjoyed learning about EAS in general and how to operate the ENDEC. With just a bit of money, I’ve got enough printer supplies to last quite some time and the best part is that this isn’t tied to any kind of subscription or fee-based service.

Happy hacking!

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