RFI

It started when a talking snake began to tell me about God.

This is not a good thing. I'm not sure it is ever a good thing. In this case, it was every single channel of the stage snake -- which I'm trying to use to run proscenium microphones, monitor microphone, band needs, and drive speakers, too -- picking up a LOT of AM radio.

I tried the usual; checking the ground. Checking all the wiring for continuity and cross-talk. Walking the route of the snake to see if it was running parallel to anything bad. The only thing that did anything was lifting ground at the booth end, and that is not acceptable (if for no other reason than we need to run phantom powered microphones off it).

So did some reading up, and, yes, it does happen. There's a bit of an elephant in the room, though; for all the discussion on all the forums about what you should do to fix things, nobody seems to notice that the vast majority of cases involve foil-ground snakes. Me, I think that foil and drain combination makes a great capacitor, and that's got to have something to do with it.

Especially since a second snake, with woven shield, has an almost undetectable level of noise in the same building.

Well, that snake is the only one with the capacity we need. So back out there today with parts for more experiments. Clamp-on ferrites did nothing. From a quick analysis of the problem frequencies, I need eight wraps or more and the cable is a bit too stiff to manage that.

Adding capacitors to ground on both signal lines did help. Perhaps even enough to make the snake usable. But that means I have to take apart every single connector on the fanout, and add these caps. Plus ensure I have "shield" to chassis ground by wiring the connector shell to pin one on that end.

I ran a completely independent cable for the most critical need; the stage monitor microphone. And, well, THAT is picking up RFI as well. In the case of that mic line, seems a broader spectrum of noise, basically a white noise, with the same powerful AM station right down at the bottom of the band rising above with various rants about how Richard Dawkins is a horrible mean man and so on and so forth.

When I get back in, I'll add filter capacitors and test the ground lead on that line as well. But it all depresses me quite a bit. The theater's managers were as frustrated as I was with how hard it is to work in there and what a mess the sound system was. So we got the funding for me to clean it up. But I'm in there doing more temporary wiring (because there is a show going into tech and I can't afford to bring the system completely down while I work on it). And stuff like this happens; my brand-new wiring is showing some of the same problems I battled on the old system.

Oh, yeah. And the grenades are already selling. There's been just enough interest to scare me a little. Good thing I put a hard cap on the first run, but even then, I am one grenade away from having to race into the shop and lathe some more off.

Plus, I have to do a lot more of those stupid caps. I like the look, more-or-less, but it is a lot of finicky labor to get the plastic caps trimmed and sanded and painted up.

I did finally get around to taking screen shots off the Aliens DVD, and comparing them with my current drawing. And, yeah, there are a few places where my accuracy suffers. The rear slot, which forms a sort of "shank" between the brass end and the crimp that presumably marks the back of the actual grenade should be wider. And the front slots should be narrower, and have a v-shaped bottom.

I happen to like the flat-bottomed grooves, but I'm tempted enough to build another grenade with the new findings and see how I like that one. Another downside, though, is that most fan-made grenades have also had the flat-bottom grooves.

I've also been thinking about a different aluminium alloy. 7075 may be a little more scratch resistant, although I suspect anodizing is the real trick here.

There's also been interest at the RPF in one-piece grenade models (without detatch-able caps or working buttons). And, sure, spray paint would work on those, but this also seems like a good opportunity to try powder coating. One more class at TechShop to try to schedule in!



All in all, it is making me feel very tired.