Solarbird 
yeah that is not a number you want to see on a closed switch. that’s not a good number at all.
okay this just got super weird
all four inputs on the left appear to be hardwired together? can that possibly right? antenna, aux 1, aux 2, cable.
wtf actual
input 5 (vcr) is not so connected and is the only one acting kinda like i’d expect
what is going on
this has to be wrong clearly i must be fucking something up. maybe the board connections are extremely counter-intuitive.
NOPE THEY'RE 100% CONNECTED ON THE SIGNAL LINES 100% OF THE TIME
WHAT THE FUCK
AND TO SHIELD GROUND
WHY
where I can get to it, the conformal coating itself does not appear to have become conductive, that was my first idea because it's pretty crusty BUT that's not it
aaaaaaand everything is 0 ohms from everything else. literally everything. even once disconnected from all the later parts of the kit. so it's happening in here. but not necessarily just in here.
definitely not just in here
but the thing is
this is all DC multimetre shit and this is _almost certainly_ some attempt to do impedence matching against an antenna (in T1) and incoming device-generated RF (in T2-4) so ... I mean, the capacitors would be more transparent if anything, not less, and those are some pretty fucken tiny inductors and I don't see how ANY OF THIS is going to be useful if it's 0 OHM SHUNTING SIGNAL TO SHIELD GROUND.
none of these are components which should realistically ever fail.
whelp it's intentional
i don't understand it but it's intentional
a tiny inductor is bridging signal and shield and it's super on purpose and i don't know why
it connects signal input (actual) to... what amounts to a tiedown point for signal, and also connects shield to that same tiedown point. there are some... I'd guess microhenrys involved along the way, with no DC resistance at all.
I don't understand it but since they're all doing it on the same ground plane it means every signal input in that group of four is linked together ALL THE TIME, and I have absolutely _no_ idea what these switches are supposed to be doing, because it's true no matter how they're set.
how is this even a switch I DON'T KNOW
i honestly can't find a function for these switches. only the VCR input - which is, I note, completely different start to switchset - is connected to a switch which seems to do anything.
Honestly given the other inputs I'm starting to think "okay it'll be antenna, a video game, an RCA discovision maybe, cable input, and VCR. Cable's its own set of frequencies, they'll've set the game and discovision to a safe channel already, they won't be doing more than one at once so we can just call it good and give them pretend buttons. VCR we'll treat actually separately because they're maybe watching the show through the VCR as they record it."
?????
#rf #electronics #AdmiralSHACK #YouHaveFailedMeForTheLastTime
i mean by the time we get to these switches we have what as far as I can tell is going to the same signal on the wire for both shield ground and all RF inputs so even if the switches got all wired up (and I'm literally not convinced they are?) then... what are switches even going to do? They connect things or don't, and everything's already all connected together.
I am so confused.
maybe there is weird RF magic going on here and somehow it actually works if you don't connect two antennas up at once. The antenna hookup leopard file cabinet circuit is slightly different to the others, with an extra cap. I presume that's important somehow.
So I guess now I'm gonna decide if I can actually wire up this thing in a basic "switches do things" system? Are all these switches even real? The VCR one seems real. Are the others?
Rasmus "raek" [rɛːkʰ] SA5RJS@moira What do you want to use this switch for? Its original purpose? Or are you about to rework it to some other kind of switch?
As "You're all idiots" pointed out, it can make sense for all the circuit nodes to be shorted *at DC*. The appropriate tool to measure how much of an RF signal propagates through from one port to another is a VNA. The NanoVNA is a *very* affordable one for hobbyists, should you want to get one.
Basically it sends out a sine wave signal into one port and measures how much bounces back to that port and also how much is received at the other port. You get both the change in amplitude and phase and from that the VNA can calculate all sorts of useful values, such as complex impedance.
@raek Yeah, I was thinking about hooking up a the signal generator I refurbished and my cheap little pocket oscillator and see what I could get that way. I mean it only goes up to 2MHz but it's better than nothing. (It's an old EICO and I made it look all pretty again :D )
So something like your NanoVNA will certainly be a good idea once I have a better idea of what kind(s) of tools will be appropriate. Thanks!
@raek (The EICO, before and after. Also, it didn't work before. It does after. ^_^
@moira Nice! I like the simplicity of that "interface"!
@raek I think it's gorgeous! It's transistor era so not prime EICO, but even so, this is good industrial design.
I even made a replacement back label. turns out that particular era look might be spray shellac because I tried it on a whim and it's like "...I have seen this _so many times before_." :D
@moira Yeah, with the sig gen and scope you can already do most of the basic measurements! Video signals are usually in the hundreds of megahertz range, so at 2 MHz the signal might see a lot of attenuation if filters or tuned circuits are involved. My hunch is that you would still be able to see the difference between switched open and closed, though!