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

[Ulrich Bangert]

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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