Hi Just for reference, KTB in 1 Hz at 50 ohms is roughly 0.9 nV at room temperature. The previously mentioned 2 nV is equivalent to about 250 ohms.
Bob > On Dec 7, 2016, at 6:58 PM, Scott Stobbe <scott.j.sto...@gmail.com> wrote: > > You can buy opamps off the shelf with an input referred noise less than a > 50 ohm resistor to build up a preamp (of course you can build up something > even lower with discretes, but then it's a time commitment over a basic > opamp preamp) > > Even if your regulator is low noise if it's running with low phase margin > you can get noise peaking. > > On Wed, Dec 7, 2016 at 3:06 PM Van Horn, David < > david.vanh...@backcountryaccess.com> wrote: > >> >> >> I replaced the original caps, and I added caps, I substituted good >> Jonhansen RF caps, and Tanceram caps. >> >> No help at all. >> >> >> >> The layout and routing is as good as I could do, and the only improvement >> I could see possible would be to move one cap closer to the reg. >> >> The difference would be less than the tolerance of part placement on the >> existing pads. >> >> >> >> Fortunately this isn't a critical piece of equipment, but I want it >> working RIGHT before I put it back in service. >> >> It's a custom receiver for 457 kHz. >> >> >> >> >> >> -----Original Message----- >> >> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Graham / >> KE9H >> >> Sent: Wednesday, December 7, 2016 10:41 AM >> >> To: Discussion of precise time and frequency measurement >> >> Subject: Re: [time-nuts] Totally unrelated, but.. >> >> >> >> Remember that the internal Voltage reference in the original three >> terminal regulator designs is a Zener. >> >> (Zeners are also useful as RF white noise sources.) The regulator is >> generally an amplifier with DC feedback. >> >> If you look at the application notes on the early regulators, they require >> capacitors to ground on both the input and outputs. >> >> If these capacitors are missing, or too low in value, or not good >> capacitors at RF frequencies, then the Zener noise is amplified by the >> regulator amplifier and pushed out the output port. >> >> I would experiment by putting a good ceramic 0.1uF cap to ground, right at >> the regulator output port. >> >> >> >> >> >> --- Graham >> >> >> >> == >> >> >> >> >> >> On Wed, Dec 7, 2016 at 10:43 AM, Bob Camp <kb...@n1k.org> wrote: >> >> >> >>> 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.vanhorn@ >> >>> 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@ >> >>> backcountryaccess.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. >> >> _______________________________________________ >> >> 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.