[time-nuts] AC line distortion [Was: HP 105B Battery, the saga continues]
jn6wfo at gmail.com
Tue Oct 4 16:21:20 EDT 2016
Thank you all for the inputs. In the present case, the location is my home
about an hour north of San Francisco, California. We are in a rural
location with other homes and some small businesses (legal or otherwise).
There could be many things hung on the 60 Hz power lines adding noise to
the "signal;" whether a "city" location would be better or worse is a
question I've never asked.
To understand the situation a little better, I put my HP-5489A Low Pass
Filter on the inverter's AC output, again through the filament transformer,
and watched the oscilloscope while I dialed down the frequency response. A
filter setting of 300 Hz was enough to visually clean up the noise while
not affecting the amplitude of the 'fundamental.' I was pleased that the
noise was manageable with such a simple tool.
Continuing, I tried a Corcom 10SP1 AC line filter from my junk box. This is
a fairly large filter, weighing about one kilo. I haven't been able to find
any specs on this thing, which is somewhere between 20 and 50 years old. It
has stamped on it a code "8003," which might mean the 3rd week/month of
1980, or it might not. Anyway, the line filter took care of the noise,
reducing *both* the AC power line and inverter output distortion to 0.35%,
better than I expected.
With the fundamental filtered out by the distortion analyzer, the remaining
noise consists of a rather dirty-looking 180 Hz sine wave, obviously a
harmonic of the 60 Hz fundamental, source unknown. Much of the local
electric energy comes from "The Geysers," an area of thermal springs and
steam at the north end of our county (Sonoma). The steam drives turbines
(of course), which spin generators. Since electricity is 'fungible' and (as
the old joke goes) "few people examine their electricity closely," the
noise could be coming from anywhere. A local source is most likely, as
others have already suggested.
On Tue, Oct 4, 2016 at 6:26 AM, Scott Stobbe <scott.j.stobbe at gmail.com>
> Considering some signal generators will have 1% (-40dBc) distortion with a
> 5k - 10k price tag, your 1% is not to bad.
> On Mon, Oct 3, 2016 at 8:52 PM, Jeremy Nichols <jn6wfo at gmail.com> wrote:
> > As an experiment, I bought an AIMS sine-wave inverter for the 105B Quartz
> > Oscillator. The inverter has a built-in transfer switch that is supposed
> > allow the load to operate from the AC line and automatically switch to
> > battery/inverter should the AC power line fail.
> > In fact the thing seems to work—the output is a nice 118 VAC sine wave
> > measuring 60.189 ± 0.003 Hz and the transfer switch is fast enough that
> > 105B doesn't seem to notice the change. The "AC Interruption" light
> > light and I don't see a flicker of the 5 MHz output on my scope.
> > Just for the fun of it, I connected a filament transformer and ran the
> > voltage into my distortion analyzer. The result was about 5% distortion
> > the inverter and 1.5% for the AC line. This got me to wondering, we've
> > discussed the AC power line frequency at length but not other "qualities"
> > of that "signal.' I was surprised that the AC line had so much distortion
> > but it's a subject I've never considered. Has anyone in this group looked
> > at this? [Yes, this is perilously close to not being appropriate
> > discussion matter—sorry!]
> > Jeremy
> > Regards,
> > Jeremy
> > On 9/18/2016 4:33 AM, Scott McGrath wrote:
> >> That NiCad pack is part of the power supply and as Jeremy points out is
> >> part of the filter system. And so one needs to restore it as part of
> >> instrument as even the 28V external power supply floats these cells and
> >> trips power interruption indicator if lost
> >> Power supply is not terribly hard to fix and the small signal
> >> can be replaced with 2N 2222,3904 and 3906'es depending on rating. You
> >> don't even need a extender a Huntron tracker or similar current limited
> >> lissajous bridge will identify failed or leaky caps and semiconductors
> >> Remember HP did nothing without a good engineering reason and that plate
> >> is there for RF shielding to prevent stray sources coupling with the
> >> If a proper rebuild is too expensive I'd suggest selling it on the well
> >> known auction site rather than hacking it up as 105's have been selling
> >> the hundreds regardless of condition
> >> On Sep 17, 2016, at 10:16 PM, Jeremy Nichols <jn6wfo at gmail.com> wrote:
> >>> How did you come up with the 33,000 uF number, Perry, and is it one big
> >>> capacitor or lots of little ones tied together? The big cap will also
> >>> filter out some of the remaining ripple in the power supply that may
> >>> been managed by the ni-cad battery.
> >>> Jeremy
> >>> On 9/17/2016 3:50 PM, Perry Sandeen via time-nuts wrote:
> >>>> <snip>
> >>>> Where the nicad pack was located one can put in 33,000 uF of
> >>>> 105C caps for $20 for a buffer hold over. <snip>
> >>> _______________________________________________
> >>> time-nuts mailing list -- time-nuts at febo.com
> >>> To unsubscribe, go to https://www.febo.com/cgi-bin/m
> >>> ailman/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/m
> >> ailman/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/m
> > ailman/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/
> and follow the instructions there.
More information about the time-nuts