Ready for a deep dive behind those jarring tones that interrupt your favorite radio show during emergencies? Let's explore how the Emergency Alert System actually works.
The EAS operates on a surprisingly elegant principle: a game of telephone played with broadcast equipment. Each station monitors several others in what engineers call a "daisy chain," creating a resilient web of information sharing. At the heart of this system sits the ENDEC (encoder-decoder), constantly listening for those distinctive tones affectionately known as "duck farts" in the industry. These digital bursts carry critical data—alert type, affected areas, and duration—that your local station's equipment must properly decode and rebroadcast.
What makes today's system fascinating is its hybrid nature. Traditional radio pathways now work alongside modern digital infrastructure through FEMA's Integrated Public Alert and Warning System (IPAWS). This dual-path architecture ensures warnings get through even if one system fails. The digital side uses Common Alerting Protocol (CAP), essentially XML for emergencies, allowing for rich content including maps and multilingual instructions that traditional radio alone couldn't deliver.
Despite all this automation, human engineers remain the unsung heroes of emergency alerting. They configure equipment, monitor logs, patch vulnerabilities, and ensure accurate timekeeping—even a few minutes' deviation can cause an ENDEC to reject valid alerts as expired. As one engineer powerfully noted, "We're not just maintaining gear, we're maintaining trust. When those EAS tones play, people listen." That responsibility drives the rigorous testing, redundant monitoring, and meticulous record-keeping that keeps this critical infrastructure running day after day.
Want to learn more about different EAS message types and hear stories from the field? Follow Fully Modulated, share with friends who appreciate broadcast technology, and consider supporting our work at fullymodulated.com.
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Episode Transcript
Hey, before we get rolling, if you're into this
kind of behind the scenes stuff,take a second to follow Fully
Modulated.
Share it with a friend or acoworker who geeks out over
signal paths and, if you'refeeling generous, leave a review
.
It really helps more peoplefind the show.
This.
(00:45):
This is Fully Modulated wheresignal meets podcast.
I'm Tyler Woodward, a broadcastengineer, public media nerd and
someone who has spent way toomuch time in transmitter shacks.
Spent way too much time intransmitter shacks.
(01:07):
I've been at this since 2014,and I currently hold a CB&T
through the Society of BroadcastEngineers, which basically
means I speak fluent, broadcastsignal and broadcast networking
I guess something like that.
If you've been following along,we've talked about what the
emergency alert system is andwhere it came from, but today
(01:29):
we're going under the hood.
How does this thing actuallywork?
What's the tech backbone thatlets an alert from FEMA end up
on your local FM radio stationin seconds?
Turns out it's a mix of oldschool radio tricks and modern
IP tech, all stitched togetherin a way that somehow still
(01:52):
works.
It's not always pretty, butit's effective.
So let's continue on with ourseries here and get on into it.
Let's talk about the daisychain At its core.
(02:25):
The emergency alert system workslike an old-school game of
telephone, except with actualradios and way more
responsibility.
It's what we call a daisy chain.
Each station monitors a fewothers and when one upstream
station sends out an alert, theothers pick it up, decode it and
pass it along, kind of like arelay race for warnings.
(02:48):
The hardware that makes all ofthis happen is called an INDEC,
which is short for encoder anddecoder.
Think of it as the brain ofyour EAS setup.
It's constantly listening forcertain sources, usually a
couple of radio stations ormaybe a satellite feed.
(03:08):
When it hears a legit alert, itjumps in, interrupts
programming and plays it out.
These boxes are smart too.
You can set filters so theyonly air certain types of alerts
or require manual approval forothers.
What makes this setup powerfulis its built-in redundancy.
(03:30):
If one station drops the ball,another one can jump in and
carry the alert forward.
That's why stations take theirmonitoring equipment so
seriously.
It's not just about thelisteners, it's about being a
reliable source and part of abigger chain.
(03:50):
The header matters.
Every alert starts the same wayThree sharp bursts of digital
tones.
We call those in the industryduck farts.
Those tones carry a lot ofinformation who sent the alert,
what kind of alert?
It is like a tornado, an amberalert, severe thunderstorm
(04:12):
warning, what areas are affectedusing FIPS codes and how long
it should stay active.
Your INDEC hears those tonesand checks the info against your
station's filter settings.
If it's a match, it airs thealert.
If not, it stays silent.
After the tones there's usuallya voice message and then what
(04:36):
we call an eom end of messagetone that tells everything to go
back to normal.
But this process is picky.
If those those tones aredistorted, out of order or
missing entirely, the alertmight never go through.
That's why engineers test theiraudio chains regularly to make
(04:56):
sure the tones are clean, clearand ready to go.
Let's talk a few numbers.
Let's talk a few numbers.
According to the FCC, there areover 77 primary entry point
stations, or pep stations,across the US.
These are the big boys.
They're built to survivedisasters, have backup power and
(05:17):
get alerts straight from FEMAvia satellite.
Local stations get tested everymonth and then there's a
national test once a year.
Those big tests go out throughIPAWS and the PEP stations at
the same time.
Engineers check the logs,timestamps and signal paths to
(05:40):
make sure everything worked asexpected and if something didn't
, you better believe there's alot of paperwork.
In fact, in 2022, 17 stationsgot slapped with fines because
they didn't handle the nationaltest properly.
So yeah, eas, it's seriousbusiness.
(06:02):
So how does that alert actuallymake it on air?
Let's follow it from thegovernment servers to your local
dial.
(06:25):
Now let's talk about the digitalpath.
Today, most alerts start atFEMA Using a system called IPAWS
, which stands for theIntegrated Public Alert and
Warning System.
Emergency managers log in, fillout a form and send it out to
(06:45):
all sorts of systems radio,television, mobile phones and
even billboards and apps.
Ipause uses something calledCAP, the Common Alerting
Protocol.
It's basically XML foremergencies, for emergencies.
(07:11):
Cap lets alerts carry not justtext, but maps, images, even
video or multilingualinstructions Super helpful,
especially in diverse ormultilingual communities.
Broadcasters set up their indexto pull FEMA servers every few
seconds for new CAP messages.
If something relevant pops up,it pulls it in, checks the
filters and airs it, just likewith the over-the-air alerts.
(07:34):
And, of course, more is betterthan less.
Two paths are always betterthan one.
Here's where it gets reallycool.
Here's where it gets reallycool.
Alerts can come in either via IP, from the internet or over the
(07:54):
air from another radio station.
Whichever gets to the end deckfirst wins.
This dual path setup means evenif your internet dies during a
storm, you've still got theradio chain, and if your RF gear
fails, the internet still hasyour back.
Companies like Digital AlertSystems and Sage make index that
(08:16):
handle both pathssimultaneously.
It's like having a belt andsuspenders for your emergency
alerts.
For your emergency alerts.
Let's talk about a little moreof the stats.
Cap became mandatory for EASequipment back in 2012, and now
over 1,400 public safetyagencies can send CAP alerts.
(08:39):
Ipause isn't just forbroadcasters anymore.
It also feeds alerts to cellcarriers anymore.
It also feeds alerts to cellcarriers, signage systems and
even yes a few streamingplatforms.
But here's the thing EAS isstill the most reliable system
for reaching people withoutmobile phones or even internet
(09:01):
access, especially in the remoteareas.
During a national test, femasends alerts through both paths
so engineers can compare results.
It's basically a big nationwideA-B test and it helps find any
weak links in the chain.
Speaker 2 (09:40):
This is a test of the National Emergency Alert System
.
This system was developed bybroadcast and cable operators in
voluntary cooperation with theFederal Emergency Management
Agency, the FederalCommunications Commission and
local authorities to keep youinformed in the event of an
emergency.
If this had been an actualemergency, an official message
(10:02):
would have followed the tonealert you heard at the start of
this message no action isrequired learning something new,
(10:36):
tap that follow button and ifyou know someone who loves
broadcast tech or emergencyalert systems, send this their
way.
Speaker 1 (10:39):
Ratings and reviews also go a long way in helping
more folks find the show.
Let's talk about the human inthe loop.
(11:02):
Despite all the automation,humans still play a huge role in
keeping EAS reliable.
Engineers have to set up thefilters, check the logs, patch
the firmware.
It's not just plug and play.
Even small things like yourdevice's internal clock can mess
(11:23):
things up.
If the time is off, even by afew minutes, your NDEK might
think an alert is expired andignore it.
That's why most engineers synctheir devices up to an NTP time
server and often have a backuptime source on site.
We also test alerts regularly,simulate failures and monitor
(11:48):
more than just the requirednumber of sources and those dry
old EAS logs that are collectingdust in your cabinet.
The FCC says you've got to keepthem for at least two years.
They're your proof that alertswent out like they were supposed
to.
Your proof that alerts went outlike they were supposed to.
(12:09):
Now let's talk about stayingcompliant.
Every broadcaster files anannual Form 1 through the ETRS
system and participates innational tests.
The 2021 tests showed that over92% of stations relayed the
alerts correctly.
Most failures came fromoutdated firmware or monitoring
(12:32):
the wrong sources.
Keeping gear up to date mattersnot just for performance, but
for security.
Firmware updates now ofteninclude patches for
vulnerabilities that could beexploited to send fake alerts or
spoof a message.
And yes, things do go wrong.
(12:55):
In 2022, the FCC warned thatunpatched EAS gear could be
hacked, and it has happened.
Gear could be hacked, and ithas happened.
In 2018, someone broke into astation system and aired a bogus
zombie apocalypse alert.
Yeah, it happened.
(13:15):
More commonly, errors happendue to bad filter settings.
A 2020 NAB study found that 30%of test failures were just from
mismatched FIPS codes ormisconfigured filters.
So even with automation,engineers have to stay sharp.
A colleague of mine once saidas engineers, we're not just
(13:40):
maintaining the gear, we'remaintaining trust.
When those EAS tones play,people listen.
That's a responsibility wecan't take lightly.
Unquote.
Today, we took a peek under thehood.
(14:08):
The emergency alert system isn'tmagic.
It's a mix of legacy radio techand modern IP tools, all
stitched together by a lot ofhuman effort and a little bit of
redundancy.
Next time, we'll get into thedifferent types of EAS messages,
because not all alerts arecreated equal, from amber alerts
(14:31):
to civil danger warnings.
We'll decode what each tonemeans and why, and if you've got
a question or a cool EAS storyfrom maybe your own station, hit
the link in the showdescription and text it in.
I'd love to hear from you andmaybe in the future we can fit
it into a upcoming episode.
If you're digging the show,help us keep it going, follow,
(15:11):
share and drop a review.
You can also become a modulatorand support the podcast for
just a few bucks a month over atfullymodulatedcom.
Every little bit helps us keepthe signal strong.
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