A possible future project made me want to look for a device which can analyse inductors over a frequency range. At first I was looking at LCR meters but the more flexible ones are expensive. Then I thought I might be able to do the same with a device called a network analyser so I started looking for those. Last week this Anritsu MS4630B caught my eye. The 'calibration void' stickers looked intact and it was listed as 'doesn't power up'.
After some haggling I got it for $400 + shipping and it arrived today. Time for some testing and crap(!)... it does power up (fan running) but it doesn't display anything. That is bad because it means there could be a really serious problem instead of the simple SMPS fix I was hoping for. So lets open it up and see what is inside:
From left to right: power supply, processing unit (with cover removed) and HF section. First I checked the voltage on the batteries but these where fine. Next thing on the fault finding list: check all the connections. And BINGO! The connector with the cable to the front panel isn't properly seated so I pushed it in and tried to turn it on again:
Woohooo! YES! It powers up and all self tests passed! Great!
Now let's play a little bit with it! A network analyser is very closely related to a spectrum analyser; it basically is a spectrum analyser but it has a more precise tracking generator and 2 spectrum analysis inputs (in the case of the MS4630B switchable between 50 Ohm and 1M Ohm impedance). The MS4630B I have also has the 70dB (10dB steps) output attenuator option installed which makes measuring (for example) amplifiers a whole lot easier. You may ask yourself: what can a network analyser like this do? Well it can do many things:
- Be used as a spectrum analyser and since the MS4630B goes down to 10Hz (3Hz RBW) it is also suitable for audio
- Determine the transfer function (magnitude and phase) of passive and active circuits
- Measure equivalent circuits of inductors and capacitors (and networks) with the use of a directional bridge (already ordered).
Allowing the input impedance to be set to 1M Ohm makes it very easy to hook it up to about any circuit and take a measurement.
First I measured an elliptic high pass LC filter I made to filter 50Hz from a large signal:
Then I went for the classic RC high pass filter (1k Ohm / 10nf) and also plotted the phase:
There still is one problem I'll need to solve though: how to get a screendump from it. The disk drive isn't working (media error) but even if it worked I immediately hit the next problem: my PC no longer has a disk drive and the two USB disk drives I have tried so far where a total dissaster. It can also use a new power button. Hopefully I can get away with a standard cap.
Still I think this is a nice catch and may turn out to be a better buy than an LCR meter for my purpose (although the LCR meter would be more precise).