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Yes, I did read the whole thread, how could a restate whitout reading the
whole thread. The "restate" is also the way a do measure S-parameters. And I did say you need an angle also. reflection coefficient = Vreflected/Vincident = polar magn. and angle Whit angle I mean Phase Shift. If you can measure polar magn. and angle, there is no need to go MUCH deeper. The fact you did go much deeper is? Use of analog equipment. The question was, instead of use VNA, use oscilloscoop? Lissajous figures measurement method is very basic stuff, its stated in my scopes manuel. Work with complex numbers and Smith Chart is a hobby of me, so I know too what is a "complex load". How to construct a direction coupler, stripline, any impedance, frequency, even a direction coupler for every frequency if you only have to measure phase shift. To measure the magn. I use the bridge of Wheatstone, with a zero biassed Schottky detector diode DVM and some formules. To give 40,000 $ for a VNA is one way, do it with "things" around you with the same results, Hey isn't that homebrew? I don't think there is anything I can't measure, even noise density ! If it can't be measured, I can calculate it. Now the purpose for my reaction was, that you where going to think, hey dummy HOW did you do it? Instead of that you did reply, we where MUCH deeper.... That's the way (maybe a little unfair) I did reply, did I miss something? I learnt that you should not trough your self away, someone else will do it for you ! BTW the scope is limited to 1Ghz, digital, full of wave calculations, anything you name. Man... did you hurt me MUCH ! Would this be the end of this thread, a would not hurt anyone. Maybe I should have not reply at all, I choose the wrong "entry". "Steve Nosko" schreef in bericht ... "bviel" wrote in message ... Use a direction coupler for forward and reverse measurement. Use a 2 Chan. Scope great bandwith not nessesary, it is the amplitude that is to be measured. reflection coefficient = Vreflected/Vincident = polar magn. and angle Chris Bowick Book page 104, reflection coefficient may be plotted directly in the Smith Chart, and the corresponding impedance read off the chart. Or did I missed something? Yup, much of what was said. You simply restated it, to some degree. We were MUCH deeper...way past the basics. The scope has to work reasonably well at the frequency of interest. They can die pretty fast abofe their useful frequency. You also have to measure *phase* between the two signals. -- Steve N, K,9;d, c. i My email has no u's. "Joe Rocci" schreef in bericht news:T0eSc.4297$Kv2.4186@trndny09... Steve, A decent (not the dollar store variety) CATV splitter has directivity of about 30 dB from 5Mhz to over 500 MHZ. I think this would do the job. Joe W3JDR Steve Nosko wrote in message ... "Paul Burridge" wrote in message ... On Tue, 10 Aug 2004 01:53:44 GMT, "Joe Rocci" wrote: Here's an idea that's just whacky enough that it might work...has anyone tried it? If you have a dual-trace scope with enough bandwidth, you might be able use Lissajous patterns. The idea would be to drive the complex load through a directional coupler with fairly good directivity. A sample of the incident signal would go into the scope X input and a sample of the reflected signal would go into the Y input. With a pure reactance as a calibration load, adjust the X and Y scope gain for a perfect circle on the display. Replace the test load with a complex load, and the magnitude and inclination of the line/oval display can tell you amplitude and phase of the reflected signal, from which any other metric can be calculated. Nice idea, Joe! If it could only be made to work, you'd be a genius. -- OK Actually, this looks good as long as you have a directional coupler for the frequency of interest! Paul didn't say. (SWR Bridge, actual bridge, for lower frequencies) You'll also have to allow for the difference in location of the two samples by adjusting the line lengths to the two scope probes intil they are both at the same "distance" from the load. Judging phase shift from a circle can't be as good as simply looking at the two waveforms. The scope horiz gain can be adjusted for some nice number of divisions for each half cycle, say 9... I've got a 100MHz. dual trace storage scope, but any directional couplers around here only will be down to 130 Mhz at best... I do also have a good bridge for down to 5 MHz., (also about 1 meter worth of stretch line...so it is possible as long as the power level is within the bridge capability. -- Steve N, K,9;d, c. i My email has no u's. |
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