On 7/14/21 12:02 PM, WB2UAQ wrote:
This is a long thread so this might have been mentioned already. I bet I am way out of line. Sorry.
Why can't the measurement be made with a 50 ohm network analyzer? We're just looking at impedance so it can easily be converted to SWR or other formats mathematically referencing 75 ohms. Maybe this is what the formulas show above are doing?
It is not easy to fabricate a 75 ohm OSL cal kit using discrete components. If this is an HF app maybe.
Yes, you could do it with a 50 ohm analyzer and mathematically convert.
I'm not sure a 75 ohm OSL kit would be super difficult. You'd have to choose a 75 ohm connector family (i.e. BNC, TNC, F, I don't know what others are available, probably there's a 75 ohm N) and then do the open and short and load - probably use a pair of 150 ohm or a quad of 300 ohm SMT resistors.? You could probably *buy* a 75 ohm termination that would be "good enough" (e.g. video systems and cable TV use them by the gazillion- surely there are higher and lower quality available).
I don't know of any 75 ohm systems above L-band (CATV and DBS satellite LNB outputs).
