Network Analyser Measurements - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th December 2012, 10:42 PM   #1
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Default Network Analyser Measurements

Hi all,

Having picked up a used spectrum/network analyser just recently in a moment of big luck, I thought I'd share any meaningful measurement I'm doing with it, over time. Not many people will have access to such an instrument, let alone hobbyists, and measurements of power supply components and systems are scarce.

A network analyser is an extremly poweful tool for impedance measurements which is basically most what power supply issues are about. Looking at the effective impedance seen at the point of load, say, a chip amp's power pins, is what counts, effectively.

The spectrum/network analyser was built late '90ies by the reputed german measurement equipment company Wandel & Goltermann.
The model is SNA-2, the second model in their range which adds phase measurement capability to the earlier SNA-1. Frequency range is 100Hz...180MHz which is just perfect for audio use.

Sitting on my bench it looks like this (note that it is comprised of two really heavy 19" die-cast aluminum boxes packed with electronics to last cubic inch) :
Click the image to open in full size.
Attached Images
File Type: jpg SNA-2_on_the_bench.jpg (51.7 KB, 660 views)
  Reply With Quote
Old 19th December 2012, 11:03 PM   #2
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
The little test jig I made for capacitor etc measurement :
Click the image to open in full size.

A short coaxial cable was cut in the middle and a tiny double-size blank PCB was soldered in between, forming a tiny capacitor (a few pF at most).
One end of the coax was fed by the tracking generator of the analyser while the other end goes directly to the receiver input. System impedance is 75R. When a DUT (Device Under Test) is low impedance, fractions of an ohm typically compared to the system impedance this forms a constant current source and the voltage seen at the output is proportional to impedance of the DUT.

Plotting the transfer function of the jig alone looks like this :
Click the image to open in full size.
We can see a pretty perfect line at 0dB with a slight roll-off at the highest frequencies (above 40MHz) coming from the tiny capacitance mentionened and other high-freq effect in the measurement chain. Horizontal scale is ranging 6 decades from 100Hz to 100MHz, in 1-2-4-8 increments for the grid lines (as indicated). This setting is kept for the rest of todays measurements.
Attached Images
File Type: jpg naked_jig.jpg (22.0 KB, 635 views)
File Type: jpg naked_imp.jpg (69.9 KB, 354 views)
  Reply With Quote
Old 19th December 2012, 11:24 PM   #3
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Using a 0.1R resistor as a reference to adjust vertical dB scale to read in dB ref. 1 Ohm :
Click the image to open in full size.

Resulting impedance plot after adjusting the reference level (which just shifts the plot) :
Click the image to open in full size.
Now 0dB=1R, -10dB=0.32R, -20dB=0.1R, -30dB=32mR and so forth. Likewise, positive 10dB step give 1/3.32/10/... values.

The 0.1R wirewound is inductive as seen from it's constant slope from 400kHz upwards, the inductance can be calculated from |Z|=2*pi*f*L, hence L=|Z|/(2*pi*f). Reading 1R (0dB) from the plot at 8MHz we get 20nH.
Attached Images
File Type: jpg 0R097_MPC.jpg (23.1 KB, 349 views)
File Type: jpg 0R097_MPC_imp.jpg (68.3 KB, 350 views)
  Reply With Quote
Old 19th December 2012, 11:39 PM   #4
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
In order to figure out the "baseline inductance" I tried shorting the jig with pliers as close as possible to the cables and using a lot of pressure to get a low shorting resistance :
Click the image to open in full size.

The according plot looks interesting :
Click the image to open in full size.
There is an inductive rise again above the <10mR of shorting resistance, coming from the residual path around the PCB edges through the pliers, but the inductance doesn't seem proper in the region where it starts to emerge and it doesn't reach the 20dB/decade slope, only a little more than 10dB/decade. My educated guess is that we see the result from eddy current losses and/or the magnetic properties of the steel pliers (need to investigate that further, with a copper short things looks quite different -- perfectly inductive -- from earlier tests I made on another jig).
Attached Images
File Type: jpg short.jpg (30.2 KB, 346 views)
File Type: jpg short_imp.jpg (70.6 KB, 346 views)
  Reply With Quote
Old 19th December 2012, 11:46 PM   #5
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Now finally hooking a capacitor to it, a WIMA MKS2 type with 3.3uF :
Click the image to open in full size.

Plot looks just fine :
Click the image to open in full size.

Comparison to WIMA's spec sheet graphs shows excellent correlation :
Click the image to open in full size.
Attached Images
File Type: jpg 3u3_MKS2.jpg (25.1 KB, 348 views)
File Type: jpg 3u3_MKS2_imp.jpg (71.5 KB, 347 views)
File Type: gif swmks2.gif (15.4 KB, 344 views)
  Reply With Quote
Old 20th December 2012, 12:01 AM   #6
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Let's add a bit of lead length to the 3.3uF capacitor :
Click the image to open in full size.

The result on impedance in comparison to the previous one (overlayed):
Click the image to open in full size.
Inductance kicks in earlier (notch shifted to the left) and is about 5dB higher -- which is about twice the original value of the cap intrinsic inductance when flush-fitted to the PCB edge.

This demonstrates the capapilities of a network analyser in an impressive way. Add a mm of lead length and you'll see it instantly!

Capacitance reads as before, calculating from the falling slope via |Z|=1/(2*pi*f*C) we get find C=1/(2*pi*f*|Z|). In this case we read 0.32R @ ~180kHz ==> 2.8uF. That's "close enough" to 3.3uF, from the eyeballing employed.
Attached Images
File Type: jpg 3u3_MKS2_longer_leads.jpg (28.8 KB, 337 views)
File Type: jpg 3u3_MKS2_longer_leads_imp.jpg (68.3 KB, 343 views)

Last edited by KSTR; 20th December 2012 at 12:05 AM.
  Reply With Quote
Old 20th December 2012, 12:26 AM   #7
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Coming to the last post of today's series, a 150nF film cap (unknown brand) is paralled to the 3.3uF (1:20 capacitance ratio) :
Click the image to open in full size.

Impedance plot tells us that this is a two-sided sword :
Click the image to open in full size.

While at very high frequencies the inductance is halved (6dB down, and even more at the resonant frequency of the 150nF cap) as expected from the second "RF short circuit" around the PCB edge, we now also have a nasty resonance peak sitting at 4MHz which is 7dB higher (2.2x) than the original curve of the 3.3uF alone. The high quality of the caps is in fact a problem here, there are close to zero ohmic losses present that could absorb most of the resonant peak (at ~0.4R).

Intrinsic inductance of the two caps should be about the same based on their construction, so their notches should be spreaded apart by a factor of sqrt(20)=4.47 because a LC resoncance is at f=1/(2*pi*sqrt(L*C)). This also is confirmed by the plot in close concordance (use the plot for NO lead length on the 3u3 for this).
Attached Images
File Type: jpg 3u3_MKS2+150n.jpg (25.5 KB, 345 views)
File Type: jpg 3u3_MKS2+150n_imp.jpg (68.2 KB, 342 views)
  Reply With Quote
Old 20th December 2012, 02:51 AM   #8
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
These are wonderful tools that teach us a lot about components.

Anything with area has capacitance.
Anything with length has inductance.
Ground is only ground for a short distance.

Thank you for posting these pix.

I hope everyone views them.
__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote
Old 20th December 2012, 07:56 AM   #9
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Excellent measurements! It is indeed a very nice piece of kit.
I assume you will at some point go forward to measure actual power supplies and decoupling effects, looking forward to read about that!

jan
__________________
I won't make the tactical error to try to dislodge with rational arguments a conviction that is beyond reason - Daniel Dennett
Check out Linear Audio Vol 7!
  Reply With Quote
Old 20th December 2012, 09:28 AM   #10
diyAudio Member
 
Join Date: Aug 2010
Thank you for your post. It was a good mini tutorial.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Visual Analyser, LX.1690 Analyser kit and other MAGICS!!! fotios Parts 8 18th March 2008 01:48 AM
Visual Analyser & Nuova Elletronica LX.1690 KIT Oscilloscope + Spectrum Analyser fotios Solid State 25 9th March 2008 07:35 PM
Which Spectrum Analyser?? fmak Parts 25 1st April 2006 04:08 PM
Audio analyser Mattwong Parts 8 19th December 2003 09:24 PM


New To Site? Need Help?

All times are GMT. The time now is 01:44 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2