Long, very very long story short, the transmitter was ALL JACKED UP and then something downstream got mad… but what?


(I actually fell asleep with my finger on the H key for a moment)

So, three days and a grand total of about 6 hours of sleep into a 5 day work week with ugly overtime that should have been 4, I came in and one of the two transmitters had SHIT ITSELF. It was putting out like 19% normal power. Curious. Logging in and taking a look around, I saw that the B side had cut out and would not come back on willingly. It was time for a quick visit to the site that would turn out to be 12 1/2 hours of grind for no benefit.

y u no make watts


Here’s the poor thing in question. Ignore the red toolboxes, they aren’t part of the transmitter, but this is the system. Note the big blue cabinet at right, it’s a Bird “Digital” air load, and it corresponds to the resistor logo shown between the A side and B side in the diagram above. It’s the main reject load that will dump any power resulting from an imbalance in the system. The combiner is the big black chungus (it’s kinda X shaped if viewed from below) above the right side of the transmitter cabinets. The black object above the Bird load is the antenna switch, corresponding to the “baseball” switch on the right side of the diagram – it lets you select between the main liquid cooled test load (not seen in the picture, it really doesn’t look like much either – just a weird canister with two big hoses) and the antenna system.

This is the architecture. The temporary line that bridged the A side to the Space Station Toilet is seen near the top of the picture. It was used when the Space Station Toilet was replaced with the Great Wall of RF or whatever the hell that thing is. It looks like the above transmitter but taller and newer. I dunno. It’s a combined bunch of ULXTE cabinets and Just Works.

So, the reason this temp line came into play and I noted it here is that this transmitter had to play double duty for a little while. It’s basically two independent ULXT-40 transmitters combined with this MSC2 interface in the middle cabinet to be one bigger transmitter. While the Space Station Toilet was being removed and replaced, the A side was its stand-in. The B side remained in place and I guess had been set up to bypass the X shaped hybrid combiner.
The vertical rectangles before the filter are the boxy hybrid couplers (?) seen above the cabinets in the photo and the resistor symbols correspond to the big tall vertical Bird loads on the shelf. The resistors here are big enough to definitely not be futile.

Later on, it was restored to its combined state, and it came back on and started making the Bird aircooled load go start roaring away, battling the air conditioning.

ORIGINALLY, its fans barely had to run at all.
And finally, the transmitter noped out.

The original cause was the B side tripping out on high VSWR. I was suspicious of why that happened but the A side did not report unusual reflected power.
I got it running again at 100% power, but I noticed about 3KW being dumped into the big blue Bird load. When either side is off, approximately 50% of the running cabinet’s output gets dumped in the Bird.

I switched to the main water cooled dummy load after turning up the aux site, and was trying to get both A and B to run together into the load without much luck. After an initial call to GatesAir support, I pretty much just had a recommendation to power cycle everything. After power cycling everything…. the A side came back with no web interface!!! It just threw a generic 404 error. Now the central controller thing couldn’t see it anymore either, probably due to missing software. It still booted up enough that I had a web server, just with no content. I was able to telnet in and get some screens of readings and commands, but that was it.

At this point I had the support person very stumped…. but finally I remembered there was a much less documented interface on that server at the path /isp/.
It let me flash the firmware again, and now I had a web interface in the normal location. Weird, right? More like HHHHHHHHHHHHHHHHHH—–

Now I could try to turn BOTH on from that DualTran interface! Perfect. Oh wait, they both fall on their faces with their ON / OFF lights wigwagging in unison like a railroad crossing, three retries then cutting off. After some fighting with it I got both to work at reduced power, screaming of excessive dissipation in the reject loads pretty much all the way back through the system.

I was on the phone with GatesAir support and the support person told me to just not pay attention to the reject power going to the Bird. Oh, sure—

….say, this looks like a phasing issue, right?

……..boy, that required some pretty coarse adjustments to do it, but the reject power is peaked towards zero…

…………did anyone before me ever bother to check the phasing???


WHO HURT YOU? Geeeez. After over an hour of rephasing things via a really wonky slow interface, I had it looking REALLY good. It was gleefully yeeting 60 kilowatts of heat out into the evening sky via the outdoor heat exchangers.

Also at some point I was stuck for hours trying to figure out why I was getting an “EXT FAILURE” interlock stuck on one, then both cabinets, and eventually tracing it back to invalid configuration settings on the MSC2 – they corresponded to a combiner with phase shifters, which the weird X shaped thing doesn’t have, so of course there were no interlock switches connected to the combiner interlock as there was nothing to protect with an interlock. It was a Fnord Failure so you just can’t see it, and I kept trying to figure out if it was the interlock on the baseball switch…

also I kept suspecting some of this stuff was loose but it wasn’t.

Time to bring the signal home!
I switched back to antenna. Now it would only run one side at a time, giving a lousy 25% or so of normal power.
Trying to make some sense of it at all, I reduced power and got both to run…. only to be greeted by seeing I was sending 20 kilowatts up, and getting 4.8 back!

Switched to the load, and got 60K forward / “35 watts” reflect (which seems to be the zero point).

WELP. Now it’s time to have the line and antenna sweep tested, I think…

What blew up? And what blew up FIRST? I dunno.

I’m extremely burned out now and just kinda glad it’s not in my hands anymore.

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