A device which measure impedance and reflections on cables and antennas. Thanks to it, we are able to measure antenna and cable parametters according to working frequency and observe realtime changes. This is used for perfect antenna tunning with minimum power loses. This device has four independent graphs which may be used to monitor different parametter. We usually use just two of them.
¶ FM band settings
As we use FM band between 87,5 - 108MHz, we have to setup VNA for this frequency span. Usually, a bit more wide band is good to select. For our case, 80-120MHz is recommended. This is still realtime with enough resolution for our purposes. The main parametters that we have to set up:
- working frequency: we have two options: setting min and max frequency or center frequency and span. in our case, we can select min = 80MHz, max = 120MHz or center = 100MHz and span = 40Mhz. As we provide full band measure, seting of min and max is recommended as its usefull for all FM frequencies
- SWR measurement: we select one of four graps to follow SWR (standing wave ratio) of measured chain (plugs+cable+antenna). The value represents amount of reflected RF power that is returning bact to the transmitter if the chain is not properly set up. We usually use GREEN or CYAN graph for this
- Re+Im: it's a value of real and imaginary value of chain impedance. These are two values, so they represented thei position in 2D graph according to the frequency sweep.
Switch on VNA, you con use either touch display or navigation button on the top of the VNA.
BAND settings
- touch display anywhere, main menu appears or right side
- select "STIMULUS" to go for frequency band settings
- select "START" and enter frequency, "80" + "M" for 80MHz in our case
- select "STOP" and enter frequency, "120" + "M" for 120MHz in our case
- select "BACK"
TRACE settings
- select "DISPLAY"
- select "Bandwidth" = 1000Hz If smaller selected, it increase reslution but fps are going to be very low.
- press back
- select "Trace"
- by clicking, let active just one of four traces (they go to grey if not selected or having a colour if they active) We usually use yellow and cyan
- by last click, you SELECT one of them. That's the one with small checkbox and also the one which we go configure actually
- click "BACK"
- click "FORMAT"
- select "SMITH - Re+Im" for cyan or "SWR" for yellow graph
- press "Back"
- uncheck "Pause sweep" if selected
- click anywhere into the display out of the menu
- you mau start measure using PORT1
Repeat Trace settings for both hraph colors, that mean for SWR and Re+Im (Smith) settings
Saving settings
- select "CALIBRATE"
- select "SAVE"
- select new empty box or used one for rewrite. The name of saved profil is identified by frequency band. In our case, 80-120MHz
Load saved settings settings
- select "RECALL"
- select desired settings
Note: let displayed only traces that you use; more unised traces makesdisplay messy