I had uploaded a zipped file in the Forum's file section that has info on the matching pad, if you would care to look at.?
On Mon, 14 Oct 2019 at 12:14 AM, Starsekr via Groups.Io<Starsekr@...> wrote: I started this topic because the original thread? got hi-jacked to antennas matching.? :-(
H Walker posted? in Msg #4702
/DMR,
/Thanks for your contribution.? A previous DFU file was uploaded for making 75 ohm system measurements
/ ("50-75 Ohm_Use transformer-10.10.2019.ra").
/The uploader made special note that in order for measurements to be accurate 50-75 ohm matching pads were required on CH0 and CH1.? Does your
/mod also require matching pads/transformers, or are you applying some type of mathematical correction factor?
/
/- Herb
** Herb,? I can't find that file.? Could you give us a message number?? Have you opened it?? ? Thanks? Jim
Dr. David Kirkby posted in msg. #4540
/1) Minimum loss pads can be used to allow calibration with 75 ohm
/calibration kits. There are 75 ohm versions of both N and BNC connectors,
/and calibration kits for both available
**David, I understand the 7 db loss pads..? Would wide band transformers work also?? Coilcraft makes several, one set is sold on Mr. Kurt Poulson's? SDR-Kit site and on eBay, or maybe we could roll our own , at least for 3-30 Mhz or 6, 4 or 2 meter bands.? One pad/transformer for each VNA port used?
* Anyone.? Assuming? I understand me using pads/transformers, and calibrating at the desired impedance (75 ohms) at the test fixture, then the NanoVNA Smith chart, while showing 50 ohms is actually 75 ohms reference, and the graphs will be ref. to 50 ohms, what math operation do I do to get a 75 ohm graph and (maybe using Excel) to get 75 ohm values?? URLs or pointers to web sites are welcome.
thanks,
Jim, KA6TPR
