Previously I posted about the Dielectric dehydrator. Here’s another common model, the Andrew / CommScope …. Newer models are controlled by this honking weird motherboard.
Upper left: black top hat is the air inlet filter that Andrew claims is accessible from the front panel (big fat lie), twist cover and pull off to open. Felt element is easily cleaned. Do not oil, use dry.
Pump: A field rebuildable diaphragm pump.
Center left: vent valve.
Bottom left: Spaghetti Junction.
Center bottom: output pressure regulator.
Bottom right: Coalescing filter bowls. Accessible at front panel.
Right: Molecular sieve unit and air tank.
Top center: Humidity sensor, pressure alarm switch, power input, air output.
Just so you know I didn’t simply open this for fun, here’s what happened on this unit.
Sliiiiiiimeeeeeee!!!!! The vent valve was blocked and the unit couldn’t drain, so it threw a humidity alarm.
Water was building up in the coalescing bowls and not being purged. That line at the bottom leads to the vent valve.
How it works: The spaghetti board starts the pump. Air passes left to right through these filter bowls, actually going through them backwards best I can tell. That is to say it enters the inner part of the fiber filters. Believe it or not there is a good reason for this. It then flows through the molecular sieve unit which absorbs moisture, passes through a check valve (where?), and enters the storage tank. From there the regulator allows enough air to pass and pressurize the line. Usually it’s set to like 3 psi.
The tank pressure is gradually increased up to 40 psi at which point the controller stops the pump and opens the vent valve.
When this happens, the pressure in the molecular sieve drops rapidly with outflow to the input side. This causes water droplets to form and be ejected. The water blows back into these two bowls and is vented along with the air via the drain.
Since this is taking place backwards, the bowls are backwards so the droplets will hit the filters on the proper side and fall downwards.
There’s method to the madness, see?
To return the unit to service, I backwashed the vent valve with the air coming from the pump and a snot rocket launched out and went….. Well, it’s never been seen since. Who knows.
It works now, that’s the important part.
And now some hot electronics porn. Here’s a Harris Broadcast ATSC receiver….
Top left: RF and IF board. Right: 8VSB demodulator. Bottom: big mama power supply.
The 8VSB demodulator.
Video stream decoder and video output
Pin count anyone?
This. Unit. Was. Not. Cheap. To. Build. Daaaaaaayuuuummmnnnn
The only thing that prevented my coworker from winding up with memory channels named after colorful air-entrained car wash products is that I really didn’t like that touchscreen user interface. A+ for cleverness though. I’ve heard the Yaesu System Fusion digital mode on these radios works very well and sounds great.
I never liked how Pandora sounds. Their audio compression is pretty lossy; some quality was sacrificed to ensure smooth streaming on lousy mobile data connections.
The ad insertions aren’t coordinated with the programming either, but this isn’t such a big deal as most of them are just dry reads; it’s not like booming tones and overprocessed voice comes yelling out of there. It’s just a little odd to have everything come to a sudden pause of just some lady reading a spot over silence in between power metal ballads. Granted this also means your classical stream won’t launch you through the roof when a spot plays…
But yeah, terrestrial radio is dead and burned thanks to the new Neilsen PPM encoding systems that cause audio defects to the point of stripping guitar chords out of some songs, eight minute stop sets of ads that come across with great… Mountains of acoustic fnords… before you are returned to a six song music library that you can’t hear properly anyway.
Not that I’m bitter. Just a little bit. Okay, I am.
Some exam sessions are walk-in, others may require advance reservations.
What to bring to the exam session:
A calculator (ideally not a graphing calculator)
Your FRN number, if you have one already. This can make the filing process with the FCC faster and easier. You can apply for an FRN number ahead of time. It is not necessary to have an FRN number ahead of time, it just makes things easier.
The exam fee ($14 at the time I wrote this – not needed if you’re at a Laurel VEC session)
Once you successfully pass the exam, if this is your first license, you will need to wait for your call letters to be assigned before you go on the air. If you have an FRN number, go here and search by your FRN number each business day. Continue until it comes up. Celebrate. 😀
Here’s a story I’ve been meaning to tell for a while.
Once upon a time, there was a wonderful isle of dreams, and a television station built upon it. To carry the sounds to accompany its magically delivered pictures, there was a set of audio distribution amplifiers.
And oh baby what amplifiers they are….
And their, uh, not the best side
And now the heart:
Those of you who are like me will also notice, this is six individually transformer isolated outputs and one transformer isolated input.
Fairly simple amp stages.
The dual power supply. One regulator on each end. This is the older design; the newer one has two separate regulator cards.
These lived happily until one day, one regulator card let out a biiiiiig fart.
For comparison, this is what the other end looked like:
Oh how it stank that morning on the wonderful isle of dreams!
The finest nose on the isle located the stench and an engineer set to restoring the precious music of the angels to flow beyond it. Fortunately he found only two channels still in use, each feeding one output… Thus:
This engineer was haunted from that day by the knowledge that some very mission critical audio still runs through that stack and the amps aren’t getting any younger.
However, they are, at least, better than the modern equivalent.
The ham responsible all but vaporized a nice Flex Radio HF transceiver, power supply, and the electrical wiring in his camper. LUCKILY, nobody was injured, but it could VERY VERY EASILY have been much worse. You don’t get a second chance with contacting power lines.
No no of course not, you can’t burn things with RF unless they’re inside the microwave.
Presenting WMBM-AM, Miami Beach, Florida.
The tower stands in a courtyard behind Radio Bar. The courtyard is fully enclosed. Except…….. The bar uses it as an entrance and exit and storage area and leaves it open to the public.
Sorry for blur in these images, I was unable to stop laughing.
To the right just inside.
To the left just inside.
Note that this tower is not on insulators. It is [barely – see below] grounded. The transmitter output goes to a three wire skirt that starts well up out of reach and is fed by, uh, let’s visit that later
Kinda sorta ground. One small wire, about 6 gauge.
See that red square? That’s the transmitter output. Right there. It’s like seven feet up in that corner. You can see the two pipes in the photo above. Only a chain and defaced warning sign (not even a standard RF exposure warning sign) separate bar guests and that.
Possibly remains of an older feed to the tower…. even more exposed.
No, the tower lights don’t work.
This has apparently been how it’s stood for years.
On a side note, here’s an at&t installation. The old vault is on a berm above ground to protect it from storm surge. The VRAD, used to supply PooVerse I mean UVerse television, internet, and kind of sort of phone, not so much.