Well so far at least #3 is not true. It may be something happening below the noise floor or outside the bandwidth, but I was looking from 0-5MHz. I have 3Ghz+ available, but I wouldn't expect these parts to be that fast.
It's a mystery, but I love solving mysteries. -----Original Message----- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Wednesday, December 7, 2016 9:43 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Totally unrelated, but.. 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 > <david.vanh...@backcountryaccess.com> 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: > david.vanh...@backcountryaccess.com<mailto:david.vanhorn@backcountryac > cess.com> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
