Hi You probably have proven one of the most basic design truths: Parts will *always* oscillate just outside the bandwidth of your test gear” :). A few other possible issues:
1) Something else is oscillating and it is simply interacting with the regulator in an odd way. 2) The oscillation / noise is at a very low level and it’s below your test gear’s noise floor 3) Testing stops the oscillation Bob > On Dec 6, 2016, at 4:24 PM, Van Horn, David > <[email protected]> wrote: > > Lots of discussion on here about low noise regulation so someone may know > what to look for. > > I have a receiver which is getting a lot of interference from somewhere. > Antenna disconnected, interference still high. > After much poking around, we found that replacing a voltage regulator with a > slightly different part cures the problem. > Running that section on external battery is also fine, so it appears the > original regulator causes some problem. > We tried various batteries over a range of voltages within the chip spec, and > couldn't make it have a problem. > > I looked at the reg input and output with scope and spectrum analyzer, and I > don't see anything that indicates excessive noise or oscillation. > The PCB layout is as tight as you could ask for. Fat tracks, lots of ground, > I couldn't lay it out any better. > Replacing the input and output caps didn't change anything. > Replacing the input and output caps with parts that should be "better", like > Johanson Tancerams or tantalums has no effect. > > Just for laughs, we tried a number of different regulator chips, all new from > the reel. > The parts with the quietest and with the most noisy specs caused problems. > One part, with a noise spec more or less in the middle of the spread is the > one that works. > > So what is it that a monolithic regulator (linear) can do which is not > observable on a scope or SA, which would cause a receiver to think it's > getting a signal or significant noise in band? > Everything else in the system is shut down, I am sure the regulator chip is > the culprit, but so far I don't see how it's causing the problem. > I could just use the quiet chip and move on, but experience tells me that I'd > just have problems again down the road. That's voodoo, not science. > > > Ideas? > > > > -- > David VanHorn > Lead Hardware Engineer > > Backcountry Access, Inc. > 2820 Wilderness Pl, Unit H > Boulder, CO 80301 USA > phone: 303-417-1345 x110 > email: > [email protected]<mailto:[email protected]> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
