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

[Bob Camp]

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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