@gunrunnerjohn posted:Yep, it does indeed have modulation, a simple carrier won't get the job done. It's actually an FSK signal centered around 455khz. The base continually sends idle commands when it has nothing to say. Your best bet is to use an old TMCC command base and if you want to tinker with the amplitude, a TMCC buffer, I know where you can get these.
The commands are detailed in the back pages of the Lionel - Complete Guide to Command Control 71-2911-250.pdf
You can actually 'scope the track signal and see the commands, the bit rate is about 3,000 BPS. I'm sure there was a good reason that bit rate was selected, Jon Z. told me once, but I forget the details.
The late Dale Manquen had some great information on the TMCC system on his now defunct website. The site is sadly gone now. However, thinking ahead, I use a web site capture program to grab the whole site before it disappeared after his death. The web archive is about 650mb, if you have a way for me to FTP it to you, I can send you the whole shebang.
Thanks GRJ and oh geez. FSK is annoying to generate with simple auto-router PCB circuits. You need an XO and PLL and have to keep everything 50 ohm traces and you need a VCO to modulate and suddenly it turns into a project. Maybe I'll take your suggestion and "extract" the board from a command base instead.
So here's the "why"
I'm thinking up some kind of lionel-o-meter (exact details are fuzzy still). We have one of the signal cars (I think Dale designed it actually) that measures how much carrier is on the track, but we're finding it's not super helpful. It does a good job of making sure the layout signal is happy, but even still there is such a big diversity in locomotives. Some models have really solid antenna coupling while others just blow.
So I'm envisioning some kind of box ... say 6" X 6" and 24" long with a track on the bottom... like a square "train tube". You put the train in the tube and close the ends and push a button. The train tube would be coated with metal on the inside and makes sure the surrounding E-field isn't influenced by nearby things or the quality of the building wiring. So then once the button is pushed... some electronics slowly ramp the amplitude up of the 455 KHz signal until the locomotive indicates lock (how to detect this I'm still thinking about, maybe just a photo sensor pointed at the headlamps). The electronics record what amplitude lock was achieved at, and we have a display on top that reads out "antenna quality" on some arbitrary scale from 0 to 99 or something.
Then we tell the club members we only listen to their signal performance complaints if the antenna level is above X.
