[time-nuts] Totally unrelated, but..

Wed Dec 7 19:20:54 EST 2016

Yes, the short hand I like to use is 4 nV*sqrt(R/1000).

2 nV/rthz off a bandgap is pretty darn impressive, that includes a delta
vbe gained up ~10x.

On Wed, Dec 7, 2016 at 7:03 PM Bob Camp <kb8tq at n1k.org> wrote:

> 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.stobbe at 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.vanhorn at 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-bounces at 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 <kb8tq at 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.vanhorn at backcountryaccess.com<mailto:david.vanhorn@
>
> >>
>
> >>> backcountryaccess.com>
>
> >>
>
> >>>>
>
> >>
>
> >>>> _______________________________________________
>
> >>
>
> >>>> time-nuts mailing list -- time-nuts at 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 at febo.com To unsubscribe, go to
>
> >>
>
> >>> https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow
>
> >>
>
> >>> the instructions there.
>
> >>
>
> >>>
>
> >>
>
> >> _______________________________________________
>
> >>
>
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>
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> >>
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> >> _______________________________________________
>
> >>
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> >>
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> >>
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>
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