PITAtek

Upon having the strange experience that a new supposedly frequency agile PTek would only work on half the band (seemed almost like an exciter unlock or something when I tried to dial in 107.1?) I decided to look at the exciter card to see if there’s a tunable tank coil or something

I wish I hadn’t now

SCA and composite inputs, J9 and J10 respectively. C66 lowpasses the composite sorta by shunting everything above an unknown frequency to ground. C65 highpasses the SCA, it’s in series. The two combine at fixed yet frequency dependent levels and go down that via near C63 and R33. U7 under the board is a voltage regulator. J1 is the RF out and L1 is the DC feed to the power amplifier just out of frame.

Yeah just go right ahead and stuff the audio inputs right on top of the RF out. No big deal.

Full view of the card. The DDS is at upper left.

Think you can get away from having your audio run across the butt of a voltage regulator by using the XLR jacks? No.

The trace going down the via next to R81 is one of the audio channels, and it runs right under the header connector for power and data to the board.

A word on this PA. This is a new LDMOS transistor from ST Micro. As such, its dissipation is really low, and it basically gets heatsinked by the leads and traces. Here’s the reference design…

What you get is significantly less copper. The big ground planes that’d soak heat away via the source leads are just not there… so a weird block thing was sandwiched under the board and I don’t even want to look at this any more

The stereo generator used to, in earlier designs, be based off a DSP that I’d heard they couldn’t get anymore. This stereo generator is what I could best describe as “deconstructed BA1414 feeding a high speed ADC”. I’m guessing the two PICs are used for timing generation and the 8 bit ADC, U8 / DAC0800LCM is probably used to generate a sine wave from a lookup table or something. conspicuously absent is any sort of audio filter to roll off program content above 15-18 khz, if this is present the generator flips the hell out. It’s a living nightmare on green circuit board. Gaaah.

Side note– the BA1414 I mentioned above is a chip made by Rohm which is used in a lot of really cheap little FM transmitter baubles and produces TERRIBLE output. It performs stereo multiplexing using a couple of poorly filtered square wave oscillators that are mixed with audio.

A quick survey…

Looking to see what the first steps are in restoring our stations to service….

Watch that first step.


We were all kinda amazed with this smoke-spewing hole. It’s the root system of a pine tree that started burning underground. It’s likely that this will eventually cause the road to cave in a bit and require filling/excavation.

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Not quite as bad… Shasta Bally

As the Carr fire continued in Whiskeytown, we had no power to our site but a remote control continued operating on the generator. The final data I got from it showed 140F stack temp above the transmitter and 122F at its chassis.

The cause: burnination.

Thanks to Matt at Valley Industrial Communications for these pictures and for being a far braver soul than I…

Hey look, it’s still got a roof!

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66 block stupidity

I need to find whoever decided to make both 66 blocks with the split down the middle and blocks without it with no identifying mark as to which type is which and pour glitter* over their head.

At left: no split. I’d been putting bridge clips on it for no reason and got a rude surprise (Zeppelin on a country station!) when I expected to have the left three pegs and the right three isolated.

At right: has the split. You have to install bridge clips to join the two sides.

* Biodegradable glitter of course – the sugar or seaweed based kind

Ow. Stop that. Stop that right now.

Just got some CCTV video of the Shasta Bally site. In about three minutes’ time it goes from smoke simply rolling over it to firestorm and *NO SIGNAL*

The high temperature reading I saw at the stack of the transmitter that was powered off was likely due to the vegetation behind the building burning. The vents are on its right side. The building is visible at the bottom center.

I’ll see if I can export and convert this later. It’ll be a while before I find out what’s still up there…

Educational Media Foundation are great people

EMF (parent network of K-LOVE and Air1) lent us their tower on wheels to get our missing stations back up!

I’ve heard it’s sat waiting in their parking lot in Rocklin for a long time waiting for such an incident. Now it gets a chance to shine! 🙂

Thanks, EMF.

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