[time-nuts] Isolation achieved by opamp based isoamp?

Stephan Sandenbergh ssandenbergh at gmail.com
Fri Nov 29 08:46:17 EST 2013


Thank you all for the comments, articles and numbers on real opamp setups -
I find it really helpful.




On 24 November 2013 17:29, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> Switch over to 60Hz power and I’ll bet those spurs move to 120Hz.
>
> Anything with a rectifier in it can produce (but may not produce) nasty
> current spikes at 2X the line frequency. What you are seeing is magnetic
> coupling of those narrow pulses. Is it coming from the switcher in the amp
> or something else? Hard to tell without some fancy line isolation equipment.
>
> Bob
>
> On Nov 24, 2013, at 8:20 AM, Ulrich Bangert <df6jb at ulrich-bangert.de>
> wrote:
>
> > Stephan,
> >
> > I made me a DIY distribution amplifier based on AD8007s. Mine achieves a
> > typical >90 dB output to output isolation and a typical >115 dB (any)
> output
> > to input isolation @ 10 MHz. The phase noise starts abt. -140 dBc @ 1 Hz.
> > The wideband phase noise floor is abt. -160 dbc and is reached at abt 4
> kHz.
> >
> >
> > There are some spurs at multiples of 100 Hz of which the biggest is -114
> dBc
> > @ 100 Hz.
> >
> > The power supply uses a switcher @ 80 kHz followed by a "voltage refiner
> > circuit". I would have expected to see the switcher frequency in the
> phase
> > noise diagram but I don't notice anything. Instead I see these 100 Hz
> based
> > spurs. I have currently no idea whether the 100 Hz is really in the
> output
> > voltage or whether it couples magnetically from the switcher's primary
> > circuit into the T1-1T transformers that I use at the input and the
> outputs
> > of the amp.
> >
> > Phase noise Measuerements were done with a TimPod 5330A and level
> > measurements were done with an ANRITSU MS2601B spectrum analyser. High
> > quality double shielded cables were used in the measurements.
> >
> > Best regards
> > Ulrich
> >
> >> -----Ursprungliche Nachricht-----
> >> Von: time-nuts-bounces at febo.com
> >> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Stephan Sandenbergh
> >> Gesendet: Donnerstag, 21. November 2013 14:47
> >> An: Discussion of precise time and frequency measurement
> >> Betreff: [time-nuts] Isolation achieved by opamp based isoamp?
> >>
> >>
> >> Hi,
> >>
> >> I'm curious about the level of isolation that is achieved by
> >> an opamp based isoamp. I'm referring to ones described here
> >> on Bruce Griffiths' page:
> >> http://www.ko4bb.com/~bruce/IsolationAmplifiers.html
> >>
> >> Anyone has a number for this?
> >>
> >> I've tried googling it, but the results are mostly filled
> >> with the other kind of iso amplifier where isolation refers
> >> to galvanic isolation.
> >>
> >> Regards,
> >>
> >> Stephan.
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