Hi Usually what happens is you have a broadband oscillation at 3.5 to 4 GHz (based on your 3 GHz upper limit). The “munge” mixes with this and that creating interference at RF.
Bob > On Dec 7, 2016, at 1:28 PM, Van Horn, David > <[email protected]> wrote: > > 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:[email protected]] 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 >> <[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:david.vanhorn@backcountryac >> cess.com> >> >> _______________________________________________ >> 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. > _______________________________________________ > 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.
