RF is Fucking Weird

I mean seriously, you’re telling me it’s possible to combine the output of two transmitters and NOT allow RF to directionally flow the wrong way out of the system like letting the output of one of the transmitters appear at the other? Of course you’d have to go and call one of the systems for this a Magic Tee Combiner.

And then you have this one that’s also filters made of giant metal tubs. What magic is going on? Seriously? I hope whoever gets to sit there with an analyzer and tune all those gribbles gets paid very well for this because they’ve deserved it for going this far down the rabbit hole. My brain would just blow a capacitor.

Fnord.

Out of sight, out of mind

This is certainly a thing. I don’t know how half this crap even got up here.

This is mostly just a picture dump that begins beyond the read more tag. This is weirdness like 1600 feet up a tower inside a weird triangular room wrapped around it.

But first, one of the more unique elevator controllers I’ve seen.. the red cylinders are crystal filters of some sort used to detect control tones that are inductively coupled by a plate on the cab that rides next to a wire stretched along its path up the tower. It works pretty well as long as everyone remembers to keep the cab panel batteries charged.

From here on just remember “treat your fiberoptics with more respect than this please”

Read more “Out of sight, out of mind”

AMazing!

These photos are from fellow engineer Chris Hall. The owner of an AM station reached out to him for advice after a contractor from two states away rebuilt the transmitter facility and it just wouldn’t make power. Wonder why? What’s the dielectric strength of a Mason jar? Which parts went Exxon Valdez in there?

My experience with AM antenna systems is limited but I can say that I would not trust even a single component in this ATU – it’s probably all been compromised by excessive voltage, current, and, uh, mechanical abuse, fire, and overheating. Call up Kintronic Labs, ask for a quote….

How do you do that to a poor innocent vacuum variable cap?! I mean uhhhhhhhhh. What. I’m guessing the voltage flew off the handle when it ran far off resonance, I can’t even fathom which part would have failed first, or maybe if the contractor just tried to bring up full power with the Vise-Grips not clamped on or okay that’s it I’m done I can’t even. This is why I like coming up at the lowest possible power first if in doubt….

Fontabulous

Just when you least expect it, what’s basically a portable scalar network analyzer starts talking to you in THIS FONT and you start disbelieving your own eyes:

Wonder if that’s from that Microsoft core fonts package that they made freely available years ago then pretended they didn’t
Oh by the way the antenna is …. Uh. It’s… not?

Root cause of that scary looking reflect plot was revealed by a quick walk up the stairs to the roof to be an almost completely disintegrated piece of LMR-400. My coworker assured me it worked perfectly fine five years ago……..

visualizing data, irritatingly

Which looks sillier to an uninitiated observer, the results of this butt-dial Google search or my mess of a DMR radio codeplug?

In other news, buzzard puke alert! Changing the “Radio IP Address” field in Motorola TRBO CPS is not how you change the repeater’s Ethernet IP, it’s just how you get it to throw blank error messages with no explanation. Well that’s a solid block of fnord.

Subchannel flatulence

Quality observation by my fellow engineer (also a radio survivor):

Music that’s been previously compressed to mp3 sounds like butthole on an HD Radio channel.

Music that’s been stored and played out uncompressed sounds like mere butt cheek on HD Radio.

And here I was thinking it just sounded like a foam cloth top brush with too many pieces missing.
Picture unrelated.

May I just take a microsecond here

Hey, it’s me, I want to give you some good frequencies. (The part I’m referring to is the very end, and the bandpass filtered beat you hear in the background is the beat to Eple, which follows it on the album. Eple will sound familiar to anyone who’s ever fired up a fresh install of Mac OS 10.3…)

But all that aside, this is about metrology and frequency standards and things my cat likes to loaf herself on top of because they’re warm.

We’re preparing for the installation of a new GatesAir Maxiva DTV transmitter at work. I was gonna say it’s an ATSC transmitter, but… I’d at least like to hope… it’s ATSC3 ready, whenever that rolls out. Sitting in the space it was going to reside in was a weird old Axcera transmitter that never worked right and was yanked out in pieces to be e-waste’d. Sitting on one of the pallets of refuse left over was the reference oscillator for the exciter, which, interestingly, was just a standalone thing without GPS synchronization. The tub in the middle is an insulated chamber containing an oven controlled crystal oscillator. Basically, this is an oscillator in a thermostatically controlled heated chamber that keeps it stable. It MUST be allowed to warm up to full operating temperature before use, or, well… it just ain’t gonna be in spec!

(insert commentary here on how silly it is that I’ve seen OCXOs in battery powered equipment that has a shorter battery life than the warmup time)

Most modern stuff uses GPS sync because it’s a good inexpensive way of obtaining a stable reference frequency and timecode. The usual arrangement is to have a voltage controlled oscillator that’s PLL locked to a 10khz timing signal output from a GPS receiver head. Aside from a little bit of phase noise possible in the system, it’s always spot on. This is why you’ll see funky little cone shaped GPS receiver antennas all over the place at broadcast facilities.

Here’s the Evertz system we have that takes GPS time and frequency references and generates our facility master clocks, black burst, and trilevel video sync. I’ve never really gotten that good a look at the way it operates but I think the black burst is generated inside the automatic changeover unit which also has some distribution amplifiers in the back as well. One of the outputs is a 10.000.00000 (I’m not sure how many significant figures) reference which can be used by a wide range of equipment. After having an, uh, experience, with one of these changeover units (see link above) I wisely do not even look at it hard while we’re in anything but 4:00 AM Sunday morning backwash programming. A frame of Grass Valley distribution amplifiers near it is used to distribute its black burst, LTC timecode, and 10mhz signals to where they’re needed throughout the facility.

This will come into play later.

The toroidal power transformer has two primary windings which were series wired for operation on 240vac. That’s why it says 240 on the AC terminal block shield. I swapped them to paralleled for 120.

More pictures and calibration process — onward

Read more “May I just take a microsecond here”

Like a spark in the dark

Something I noticed recently…

WiGLE added Bluetooth device scanning and database functionality to their Wardriving app a year or so back. Originally, I would see a few things pop up in it, usually headsets and car entertainment systems.

Now, it seems like everything comes with Bluetooth and no fecking power switch.

This is the result of just leaving scanning active overnight as people and their Bluetooth devices move past. The newer BLE stuff has…. kinda terrifyingly long range.

It makes me think… If WiGLE is scanning this for nerds like me, there’s gotta be some shady-ass analytics company using Bluetooth to track everyone without their consent and selling that data.

Personally I use maybe three Bluetooth devices regularly, and they are all switched off when not in active use. Without trying to correlate addresses to vendors or anything, I’m just going to empirically blame Apple’s crappy AirPods for a lot of these potential tracking beacons.