I've got parasites

FM radio station, most likely.

Sometimes the easiest way to track down low-level stability problems is to "build" your circuit in LTSpice. LTSpice has the advantage of perfect immunity to environmental effects.

-- jm

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- I don't know of one any of siginificant power nearby. I'm not in a big city. The college has one but I don't think it's that strong.

There is a local AM geezer (WGEZ, really!) radio station that gets into just about everything, but being a non-relatavistic rate of voltage change, I can squash that easily enough in most cases, including here.

For Pete's sake I can't even short the VHF signal at the scope connector, how does that work!?

At any rate, as much as it has to be an external signal, how would you explain the keying effect when the drive circuit is turned on? The local circuit would have to be acting as a passive resonator or something!

Well, that won't help much, because I already know the circuit works, on paper and in reality. Besides which, simulators tend to go with perfect connections. I don't know about LTSpice in particular, but I'm guessing it wouldn't know the difference if I had one of the MOSFETs on the other side of the room on some ten foot pigtail leads.

Tim

-- Deep Fryer: a very philosophical monk. Website:

how far away is it?

And what about if you disconnect the probe complely from the scope...see it then?

Mark

You mean, you remove probes and all connections to the scope and short the BNC connector at the scope with, say, a screwdriver and the problem is still there? If yes, the problem is internal to the scope.

There is usually a switch near the input that selects DC/AC/GND. Put it to GND. Still there? Yes = scope internal problem.

Cheers, John

Set the trigger right, and see if you can resolve the frequency accurately. Now, tune a FM radio to that freq, and see if it is or isn't.

It's obviously the spirits. Try running it through an audio discriminator, or maybe a reverse flux capacitor arrangement, and see if you can discern what they're trying to tell you.

Don't forget the hat, of course:

Cheers! Rich ------ "Teddy Kennedy: A Blond in Every Pond!"

What? Are you saying that if you directly short the input connector of your scope to its own ground, you still see the noise?

The scope is broken.

Sorry, Rich

DO NOT STICK A SCREWDRIVER OF ANY KIND INTO A BNC SOCKET!

Don't even use a paper clip. It will damage the contacts.

Find a piece of #24 or smaller bare copper wire (these are abundant in telephone trunks, which you can usually find lying in the crap pile at construction sites), and maybe an alligator clip; poke the wire into the socket hole, and bend it into intimate contact with the shell.

Good Luck! Rich

Shoould he use the scope probe for an antenna? ;-P

Cheers! Rich

Sorry for the confusion, I was using a tee connector. Still, that's balls-all inductance, I don't see how the signal can get past a short like that, at least for another few hundred MHz.

With no antenna, or the input GND'd, it shows no signal. Even a 2" stub of wire will register a signal.

BTW: there is a college radio station a few blocks down the street(!), but I don't know how strong it is (tell me, how many FM radios do you own that came with AVC and an indicator? ;).

Does anyone have an explanation how the induction drive circuit appears to be amplifying the signal in modulation to the drive output?

Tim

-- Deep Fryer: a very philosophical monk. Website:

I tried just about every appliance in the house, including the network (the CAT5 does happen to run quite near the experiment... which caused network troubles when I was playing with small CW Tesla coils ;), but there was no change.

Tim

-- Deep Fryer: a very philosophical monk. Website:

Turn your TV to channel 6, and listen as you watch the trace. :-)

Or, turn your TV _off_. (or maybe your computer. and unplug the microwave and VCR.) ;-)

Good Luck! Rich