10388	2014-10-26 12:18:15	Weddig, Henning-C...	AW: [emrfd] Testing Xtal Ladder Filter Impedance
Message	Date	From	Subject
may be the reaso is that the filter is not unilateral, i.e. S12 is similar to S21. Henning Weddig DK5LV -----Ursprüngliche Nachricht----- Von: 'Steve VK2SJA' vk2sja@bigpond.com [emrfd] [mailto:emrfd@yahoogroups.com] Gesendet: So 26.10.2014 08:33 An: emrfd@yahoogroups.com Betreff: Re: [emrfd] Testing Xtal Ladder Filter Impedance Hi Rod/All, Rod, I finally got around to watching that video while playing with the software. Very useful/powerful stuff. Thanks. I was able to import my vna/J .s2p file without any difficulty and was looking at my filter sweep in no time. All to easy in fact. But when I went I told RFSim99 to generate a "Auto Match" -> "Simultaneous conjugate", I got the following error message:- "Simultaneous conjugate match not possible at that frequency because S-Parameters produce a negative square root in the solution." I found that if I told it to match Port 1 only it gave me values (only for port 1 of course) that were very close the the values it had arrived at by a much longer and arduous route. Anyway just wondering if there is something that I could have done to work around the error? And if you may happen to know why my filter caused a negative square root? 73, Steve. > Hi Steve, > > > Good, it looks like you have it under control. 0.2dB is better than 2dB > ripple. > > > Roderick Wall, vk3yc. > > > > > > >
10389	2014-10-26 14:16:36	radioaustralia123	Re: AW: [emrfd] Testing Xtal Ladder Filter Impedance
Hi Steve, I think Henning is correct. In that your Touchstone.s2p file is faulty. I don’t know anything about the MiniVNA as to how to generate two port s2p files. I guess it would be somewhere in the manual. You look as if you almost have it correct when you are able to do a match for one port. It looks as if the s-parameters for the other port are not correct? Roderick.
10390	2014-10-26 15:36:59	Steve VK2SJA	Re: AW: [emrfd] Testing Xtal Ladder Filter Impedance
Thank-you Henning and Rod, vna/J has what is called an "S-Parameter collector". You run an S12 scan "collect it" and then add later the S21 scan (actually they can be done in any order). Not a limitation of vna/J software but of the miniVNA Pro hardware. I will now go and have another close look at the my vna/J setup and the actual scans done. Probably need to re-do them. I suspect that I have somehow managed to do two scans with non-matching parameters. Actually thinking about it. It will be because one of the scans was done with proper calibration and the other with improper calibration. The calibration data for transmission and reflection modes is held separately and your not forced to update if you switch between modes. I think... 73, Steve. > Hi Steve, > > > I think Henning is correct. In that your Touchstone.s2p file is faulty. I > donât know anything about the MiniVNA as to how to generate two port s2p > files. I guess it would be somewhere in the manual. > > > You look as if you almost have it correct when you are able to do a match > for one port. It looks as if the s-parameters for the other port are not > correct? > > > > Roderick. > > > > > >
10392	2014-10-27 05:13:14	radioaustralia123	Re: AW: [emrfd] Testing Xtal Ladder Filter Impedance
Hi Steve, You could use RFsim99 to see what each of the following look like in your s2p file. S11 and S22 won’t be exactly the same, but if one is completely wrong you may be able to see that. Likewise with S21 and S12. On the left side select S11 and select S22 on the fight side. And compare. Likewise with S21 on the left and S12 on the right. And compare. Roderick.
10409	2014-11-03 17:31:08	Steve VK2SJA	Re: AW: [emrfd] Testing Xtal Ladder Filter Impedance
Thank-you Roderick/Henning/All, I should probably keep this to myself. But I'll share so that you can all have a good laugh. I'm reading Roderick's message below, thinking "what's he talking about comparing S11, S12... And then in a flash it all fell into place. And I burst out laughing at my own foolishness. A file with the extension .s2p would be called that because it contains S-Parameter data TWO ports. But if you use the vna/J S-Parameter collector and only collect data from port ONE, S21 and S11. Then what you really have is a .s1p file with only half the required information. So RFSim99 then has a hard time doing a SIMULTANEOUS conjugate match. :lol: You chaps were thinking this all along but were too polite to say so. Weren't you? Anyway thanks Roderick/Henning, for pointing me in the right direction!! Yes my .s2p file was indeed badly broken. As an exercise I performed a complete two port scan and RFSim99 happily predicted matching networks in both directions. And this is much easier and more precise than manually adjusting inline resistive terminations! I do have another question. The matching networks predicted by RFSim99 caught me by surprise because they were not symmetrical. Is this common, to have dissimilar matching networks on either end of a crystal ladder filter? Newbie, learning fast (and still laughing at my own antics). 73, Steve. > Hi Steve, > You could use RFsim99 to see what each of the following look like in your > s2p file. S11 and S22 won't be exactly the same, but if one is completely wrong you may be able to see that. Likewise with S21 and S12. On the left side select S11 and select S22 on the fight side. And compare. > Likewise with S21 on the left and S12 on the right. And compare. Roderick.
10412	2014-11-04 12:05:14	radioaustralia123	Re: AW: [emrfd] Testing Xtal Ladder Filter Impedance
Hi Steve, With regard to your broken s2p two port touchstone file. It looked like the s-parameters for the 2nd port were not correct. What was wrong I was not sure. Great in that you now have it all correct and know what was wrong. With regard to your question. You could again compare S11 with S22 and S21 with S12 in RFsim99 and see if the ports are the same. If they are not the same then the matching circuits will be different. Roderick, vk3yc.