Again without the HTML formatting.
Calibration of any VNA is necessary.? You have to use the open'/short/50Ohm plugs along with your adaptor cable to calibrate the VNA "system".
So the proper sequence for any VNA is:
#1 Calibrate VNA with adaptor cable (i.e. any cable that is NOT part of your antenna system) using open/short/50Ohm
#2 Measure/tune antenna (not the coax from your rig).? This will be your VNA + adaptor cable plugged directly into the antenna with no chokes or anything in between.
#3 Tune your antenna to get 0 reactance and ideally 50Ohms.? But whatever 0 reactance point you have that is the resistance you need to match.? You can usually get below VSWR 2.0 with standard BALUNS of 2X, 4X, 8X, 16X if needed but it's much better to tune the antenna to 50 ohms if you can
Note that you can get 0 reactance at multiple points -- especially on 6M and higher.
#4 Measure your coax using the the 50Ohm terminator on the antenna side and ensure you have 50 Ohms and 0 reactance...or real close to that.? Also use the TDR to ensure no breaks in the coax (pretty rare).? You do need to know the velocity factor of your coax in order to use the distance calculation in the VNA TDR.
#5 Measure the complete coax/antenna system.? Should look very close to the same as it did at the antenna.
#6 Add a 1/8th section of coax? to the system and measure again....if there is no common mode the measurement will be very close to #5.? There should be no common mode if the antenna is 50Ohms and 0 reactance.? If the antenna is not 50Ohms (or not matched to 50Ohms) and/or has reactance than extra coax will change the tuned frequency and resistance....this is why you can't really tune at the rig if your system isn't matched near perfectly.? Common mode will modify the VSWR measurement.
Note that nowhere? above do we talk about minimum VSWR -- that's not the goal.? 50Ohm and 0 reactance is minimum VSWR.? Problem is we are rarely exactly on 50/0. And some antennas can never get there without a lot of monkeying around with custom BALUNs and matching networks.? So always measure your antenna system, coax, system, system+1/8th in that order.
Mike W9MDB
toggle quoted message
Show quoted text
On Thursday, August 25, 2022 at 12:50:10 AM CDT, GMRS_two_way_radio via groups.io <sclark6389@...> wrote:
I thought I read somewhere it should be calibrated using the software if a person is going to be using the software for measurements
