Re: [time-nuts] SRS FS710 spurs at 50Hz and harmonics?

2015-10-02 Thread Anders Wallin 
Hi all, thanks for all the suggestions.
I am starting to think this is a feature not a bug.
I tinkered with the FS710 a bit today. It shows about 600mVpp 100Hz
sawtooth on the +/-13.9VDC input to the voltage regulators.
I changed the big electrolytic caps and the smaller tantalum caps around
the 7805/7905 regulators - but no change to the sawtooth.
With a 1M 10x probe and a cheap scope there is no visible 100Hz ripple on
the +/-5V regulator outputs.
some new pictures in my blog:
http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/

Maybe my earlier result with strong spurs was a result of a ground loop
between REF-distribution-amp, 3120A, and this F710-distribution amp. They
were probably plugged in to different AC outlets...

Anders


On Thu, Oct 1, 2015 at 1:52 PM, Bob Camp  wrote:

> Hi
>
> It can also be a blown diode in the bridge. When that happens the ripple
> goes
> way up. A quick check with a scope should tell you what’s happened. 50 Hz
> triangle
> wave = blown diode. 100 Hz triangle wave = blown cap.
>
> Bob
>
> > On Oct 1, 2015, at 4:04 AM, Esa Heikkinen  wrote:
> >
> > Anders Wallin kirjoitti:
> >
> >> I seem to get very strong spurs at 50Hz and harmonics with an old
> >> second-hand SRS FS710:
> >> http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/
> >> feature or bug? Anyone looked at the powersupply and figured out what
> parts
> >> to change?
> >
> > If you live in a country with 50 Hz mains network then this sounds like
> a dead capacitor in the power supply. Usually this means that it has old
> fashioned linear power supply (with classic iron transformer). In that
> case, replace the secondary capacitors after the rectifier bridge(s). Check
> voltages with oscilloscope if you wanna see which ones, but it might be
> good idea to replace them all (there should't be many of them).
> >
> > Should be very easy to fix.
> >
> > --
> > 73s!
> > Esa
> > OH4KJU
> > ___
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Re: [time-nuts] SRS FS710 spurs at 50Hz and harmonics?

2015-10-02 Thread Magnus Danielson 

Hi,

I did measure the phase-noise of a FS710 with my TimePod and saw the 
same as you. Cross-correlation is a nice tool in the toolbox.


It was really clear that the OSA cesium was much cleaner than the FS710 
buffered variant of the signal.


The sawtooth is expected, and the caps just makes sure you don't hit 
rocks bottom. The regulators will damp thus further, by burning of the 
difference as heat, but it's not really perfect. If you put a 
DC-blocking cap in, you will be able to amplify the AC signal and hear 
it, it's there for sure.


The FS710 isn't really built to be ultra-quiet.

I think some of these noises is to be expected, so it is a matter how 
much, and that depends on how much effort you put in cleaning up power. 
Traditional grid-transformer-rectifier-caps-regulator setup will create 
this 100 Hz, and all we can do is to toss caps (yeah, and inductors) and 
regulators on this. A switcher can change this equation, even if the the 
50 Hz rectification process is still there.


No wonders some go for battery options, but then batteries is pretty 
hefty caps.


Cheers,
Magnus

On 10/02/2015 08:29 PM, Anders Wallin wrote:

Hi all, thanks for all the suggestions.
I am starting to think this is a feature not a bug.
I tinkered with the FS710 a bit today. It shows about 600mVpp 100Hz
sawtooth on the +/-13.9VDC input to the voltage regulators.
I changed the big electrolytic caps and the smaller tantalum caps around
the 7805/7905 regulators - but no change to the sawtooth.
With a 1M 10x probe and a cheap scope there is no visible 100Hz ripple on
the +/-5V regulator outputs.
some new pictures in my blog:
http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/

Maybe my earlier result with strong spurs was a result of a ground loop
between REF-distribution-amp, 3120A, and this F710-distribution amp. They
were probably plugged in to different AC outlets...

Anders


On Thu, Oct 1, 2015 at 1:52 PM, Bob Camp  wrote:


Hi

It can also be a blown diode in the bridge. When that happens the ripple
goes
way up. A quick check with a scope should tell you what’s happened. 50 Hz
triangle
wave = blown diode. 100 Hz triangle wave = blown cap.

Bob


On Oct 1, 2015, at 4:04 AM, Esa Heikkinen  wrote:

Anders Wallin kirjoitti:


I seem to get very strong spurs at 50Hz and harmonics with an old
second-hand SRS FS710:
http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/
feature or bug? Anyone looked at the powersupply and figured out what

parts

to change?


If you live in a country with 50 Hz mains network then this sounds like

a dead capacitor in the power supply. Usually this means that it has old
fashioned linear power supply (with classic iron transformer). In that
case, replace the secondary capacitors after the rectifier bridge(s). Check
voltages with oscilloscope if you wanna see which ones, but it might be
good idea to replace them all (there should't be many of them).


Should be very easy to fix.

--
73s!
Esa
OH4KJU
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Re: [time-nuts] SRS FS710 spurs at 50Hz and harmonics?

2015-10-01 Thread John Miles 
SRS likes to isolate their RF connectors from ground, it seems.  This is almost 
never a good idea.  When measuring PRS10 Rb standards, I've seen similar line 
spurs that went away when I grounded one side of the balanced 10 MHz output at 
the point where the DC supply was connected to the unit.   

Looking at the schematic that Orin posted earlier, it seems they've done the 
same thing with the FS710.  Try bonding the insulated BNC input jack to ground 
at the point where it enters the chassis, and I'll bet those spurs get a lot 
better.  (That is, unless you actually do have a bad filter capacitor.)

-- john, KE5FX
Miles Design LLC

> > I seem to get very strong spurs at 50Hz and harmonics with an old
> > second-hand SRS FS710:
> > http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/
> > feature or bug? Anyone looked at the powersupply and figured out what parts
> > to change?
> 
> If you live in a country with 50 Hz mains network then this sounds like
> a dead capacitor in the power supply...

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Re: [time-nuts] SRS FS710 spurs at 50Hz and harmonics?

2015-10-01 Thread Esa Heikkinen 

Anders Wallin kirjoitti:


I seem to get very strong spurs at 50Hz and harmonics with an old
second-hand SRS FS710:
http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/
feature or bug? Anyone looked at the powersupply and figured out what parts
to change?


If you live in a country with 50 Hz mains network then this sounds like 
a dead capacitor in the power supply. Usually this means that it has old 
fashioned linear power supply (with classic iron transformer). In that 
case, replace the secondary capacitors after the rectifier bridge(s). 
Check voltages with oscilloscope if you wanna see which ones, but it 
might be good idea to replace them all (there should't be many of them).


Should be very easy to fix.

--
73s!
Esa
OH4KJU
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[time-nuts] SRS FS710 spurs at 50Hz and harmonics?

2015-09-28 Thread Anders Wallin 
I seem to get very strong spurs at 50Hz and harmonics with an old
second-hand SRS FS710:
http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/

feature or bug? Anyone looked at the powersupply and figured out what parts
to change?

Anders
(going crazy measuring all things in sight with a loaner Microsemi 3120A :)
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