Another day, another case of being thoroughly perplexed by RF Central gear—
When the mast goes up but the signal doesn’t go out, it’s time to investigate.
The forward/reflect/12vdc return meter always seemed to show 00.0 if the PA was off… -1 if the PA was on, in any field.
TWO different bad amplifier units…. one was waiting on the shelf as a spare, one just came off the truck.
So what’s inside? I forgot to take a photo but if you remove the hex screws on the back it reveals a Stealth Microwave SM2025-44L, 25 watt linear amplifier for 2000-2500 megacycle DVB applications. Sadly. Stealth Microwave is long gone.
Interestingly the amp bricks are specified as having an internal output isolator. Nifty.
The other major part inside the amp brick is a bias tee that splits 12vdc power sent up the coax out to run the fan and the amplifier.
And now, it gets… horrifying.
I found a datasheet on the SM2025-44L and it’s specified as taking a mighty 8.5 amperes. I mean, at least it isn’t gonna arc furnace anything, but the voltage drop CANNOT be nontrivial anymore.
This has to get to it on the coax. The coax from the indoor unit in the truck to the outdoor amplifier unit is not a short sweet little run. See the big black coil up the mast in the first pic? There’s probably at least 45 feet of coax in there, plus another dozen at least to land it from the feedthrough in the roof to the IDU in the rack.
WHY DID THIS EVER WORK AT ALL? Or does it? I don’t….. I can’t even——- No——— I need to go home and collapse in bed and place the kitteh on top of me and stop trying to think for this week. DONE. I’m so done. What the hell.