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 < [email protected]> 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:[email protected]] 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 <[email protected]> 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: [email protected]<mailto:david.vanhorn@ > > > backcountryaccess.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. > > _______________________________________________ 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.
