Unraveling the Puzzle: When HD1 Drops But HD2 Doesn't

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Ever faced a technical problem that defied conventional wisdom? In our latest deep-dive, we unravel a perplexing HD radio mystery that had us questioning everything we thought we knew about digital transmission. 

Our HD1 signal kept dropping out randomly for fractions of seconds while HD2 played flawlessly—a contradiction that shouldn't happen if the issue was with the exciter or transport stream. We meticulously examined every component: the Nautel NV30 transmitter, HD multicast units, Omnia 9 processor, even the Justin 808 time alignment system. Everything checked out perfectly with no errors in logs, yet the problem persisted.

The breakthrough came when we discovered our monitoring equipment was giving contradictory information. The Inovonics 632 receivers consistently showed dropouts while the newer 551 mod monitors worked flawlessly. After consulting with colleagues, we uncovered the truth: the 632 tuners had a known flaw the manufacturer never publicly acknowledged. Meanwhile, HD2's natural advantage of a larger buffer (around 40 seconds in MP1 mode) provided greater resilience against minor data issues.

This experience highlights a frustrating reality for US broadcasters—we're locked into proprietary HD radio technology when other countries enjoy open digital standards with multiple competing manufacturers driving innovation and affordability. Norway transitioned to fully digital radio back in 2017, while we're still troubleshooting proprietary equipment quirks.

What HD radio equipment challenges have you faced? Have recommendations for reliable monitoring gear? Text us using the link in the show notes and share your experiences!

📚 Learn more:

Learn more about HD Radio: https://en.wikipedia.org/wiki/HD_Radio

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Episode Transcript

Speaker 1 (00:00):
Ah yes, hd radio.
It's supposed to be the goldstandard in digital radio
transmission, right?
Well, like any tech thatpromises to be the future, it's
not without its quirks.
In today's episode of FullyModulated, we're diving into an
ongoing mystery with one of ourHD stations and, trust me, it's

(00:22):
been a real puzzle.
For some reason, our HD1 audiostarted dropping randomly.
But here's the kicker HD2 neverdropped.
Let's get into what we'veuncovered and why.
Despite some of the bestequipment, this was far from
easy to figure out.
The kicker here if it's atransport or an exciter issue,

(00:43):
it should affect both HD1 andHD2, right?
Well, that's not what we wereseeing.
Let's break down the issue, thehead-scratching moments and the
conclusion we're slowly butsurely stumbling toward.
So the first sign thatsomething was off came from one

(01:33):
of our nearby offices, whichreported that HD1 audio was
dropping intermittently.
This wasn't your typicalfull-on dropout where the
station just goes silent.
This was more like a briefglitch lasting anywhere from 0.3
seconds to a full 3 seconds.
But what made this problemespecially tricky was the fact
that HD2 wasn't dropping.
Now you know the way Iunderstand it.

(01:55):
If the issue was with thetransport or the exciter, or
even a problem with the XGencard.
It would take out all HD, notjust HD1.
It wasn't adding up for us.
We looked at all the gear in theair chain and the more we dove
into it the more confusing itbecame.

(02:16):
The Inovonix 632 HD receiver,which is part of the setup for
our confidence, feeds back tothe studio, to our partner
organizations, that wasconstantly dropping hd1.
But the inovonix 551 modmonitor that we just got didn't
have any of these issues.

(02:36):
Everything on the transmitterside, the nautil nv30, the
nautil hd multicast and theomnia 9, it all checked out
perfectly.
Everything was up to date andthere were no faults or errors
in the logs.
It's moments like these when youstart questioning everything
you know about how radio shouldwork.

(02:56):
You're looking at one channeldropping and the other working
fine and you're just kind ofstanding there left scratching
your head going what am Imissing?
Now here's where things geteven more puzzling.
The enovonix 632 hd receiverwas showing the dropouts.
That was a clue.
But the 551 mod monitor, noproblem, it worked fine.

(03:19):
It wasn't dropping hd1 at all.
So what was going on?
Was the 551 just better athandling the HD radio data or
was there really an issue withthe 632 receiver In
troubleshooting.
The key difference was the factthat the 632 doesn't blend back
to analog FM like other HDradios, so when the dropout

(03:43):
occurred we could hear it rightaway.
The 551, however, might be alittle more forgiving, hiding
glitches because of how itprocesses the audio.
If you've ever had issues withHD radio gear before, have you
noticed similar oddities, maybeone channel misbehaving or a
certain receiver acting up?
I'd love to hear yourexperiences.

(04:05):
Drop me a line.
You can text the show using thelink in the show description.
At this point we turned ourattention to the core of the
transmission chain the NautilNV30 transmitter and all the
related gear.
After checking everything, weconfirmed there were no faults,
errors or lost packets.

(04:25):
Everything was running smoothlywith no issues flagged in the
logs.
The Nautil HD multicast wasalso operating as normal and the
Omnia 9 had been rebootedwithout any improvement to the
audio dropout issue.
So if it wasn't the transmitteror the processor, it had to be

(04:48):
somewhere further down the line.
So, of course, next we went tothe Anavonix Justin 808, which,
for those that don't know, the808 is responsible for automatic
HD1 audio gain adjustments andtime alignment to ensure
everything blends smoothly whenyou lose HD1 and have to go back
to the analog FM signal.

(05:08):
So we bypassed the Justin 808and while the dropout issue sort
of decreased, it didn't go awayentirely.
Or it was just me hoping thatit would be the culprit and
solve things a little easier,which of course didn't work.
This left us wondering maybeit's just a 632 HD receiver?

(05:29):
This is the part where you getinto that troubleshooting loop
you know what I mean where youkind of tried everything
rebooting the gear, bypassingcomponents and were still no
closer to figuring out what theroot cause was.
When something's dropping outintermittently like this, you
can waste a lot of time chasingdown red herrings and going in
loops.

(05:49):
It's enough to make you feellike you're in a maze with no
exit.
As we continued digging, welearned that the issue might be
related to the Inovonix 632receivers, because nothing else
made sense.
The more we thought about it,the more it made sense overall
to all of us.

(06:09):
The tuners just couldn't handlethe data properly in the way
that the 551, the newer modmonitors could.
A co-worker of mine at apartner organization mentioned
something that kind of made usstop and think.
Hd2 likely doesn't drop asoften because it has a much

(06:31):
larger buffer in the MP1 modeit's around about 40 seconds
compared to HD1, which doesn'thave as much room for buffering.
Have as much room for buffering.
This gives HD2 a bit morewiggle room to recover from when
it has any sort of minor issues.
It turns out that the 632 tunerswere known to have this flaw.

(06:56):
The company had reportedly beenaware of the issue, but never
publicly admitted it.
This was a big moment ofclarity for us, but it also left
us with a big question markthat may have bigger
implications.
Do we trust this company withfuture monitoring gear?
And you know what.

(07:16):
This is part of why HD radiofeels so clunky.
It's all proprietary gear thatlocks us into certain
manufacturers, makingtroubleshooting harder than it
needs to be.
What we really needed here inthe US is an open digital radio
standard, something like whatthey have done in other

(07:37):
countries, instead of relying onone or two companies for all
the equipment.
We'd have multiple competitorsin this space, driving
innovation and making gear moreaffordable.
And, who knows, maybe by nowwe'd have a full digital radio
nation, like Norway, who wentdigital back in 2017.
All digital, shut the FM offand everything, but here we are

(08:01):
still tangled up in inproprietary systems and alright,
you know what I'll get off mysoapbox.
But I think you get the point.
It could have been better, much, much better.
Now, as we stare down thismystery, we're also eyeing up
the new Anovonix 679 HD radiotuner to see if that will solve

(08:23):
our problem.
Maybe a newer HD radio chip,the 679, promises to address
some of the issues that arenagging us with the 632.
It might be the solution we'vebeen looking for.
But here's the thing.
I'm also curious if anyone outthere has experience with HD
radio tuners commercial HD radiotuners that we could use to

(08:48):
monitor our feeds.
If you've got a favorite brand,a model or even just a good
recommendation for reliable gearused to monitor your HD signals
, drop me a line.
I'd love to hear about it.
You can text the show using thelink in the episode description
.
Maybe in a future episode wecould do a full gear comparison.
So what do we do with all thisinfo?

(09:11):
The takeaway here is that withHD radio, things aren't always
as straightforward as they seemto be.
In cases like this, where onechannel works perfectly fine and
the other doesn't, it's often avery certain issue with a
single piece of equipment, inthis case, the inovonix 632
tuner seemed to be the culprit,but it took some deep digging to

(09:34):
figure that out, and even evenafter all that, we had to
question the reliability of thegear we're using moving forward.
That's it for today's episodeof Fully Modulated.
Sometimes, troubleshooting HDradio can feel like solving a
puzzle, but the more pieces youget, the clearer the picture
becomes.

(09:55):
If you've run into similarissues with your HD1 or HD2
signals, or if you've had issueswith HD tuners that weren't
exactly advertised asquote-unquote junk, I'd love to
hear from you.
Stay tuned for more and, asalways, check the description
for links and extra details, andI'll see you next time.