I recently build a Loop antenna for CB radio, or at least i tried.
Its made out of a 80cm diameter Loop of RG58 Coax (shield and core connected at the ends), a Coax stub condensator and a unshielded wire primary loop.
When i put my SDR on it, it seams to have way to much of a wide reception (calculator said it would have only like 40-50khz wide reception band).
When i put my analog power/swr meter on it, it claims to have a SWR of 1.2 and takes about 3.5W of power (compared to my dipole taking 4W).
But when i put the NanoVNA on it to get a more accurate reading of SWR, all i see is a flat line that claims a SWR of about 50.
When i pump up the stimulus frequency up to 300+Mhz i get some SWR dips there down to 1.6, but i assume thats just the Primary loop resonating.
Any idea why i get results on my analog SWR meter but not on the NanoVNA? Is the NanoVNA maybe putting to few power into the loop to make it resonate?
i’ll add that in a way SWR chart is more resistant to misuse, because if nanovna is calibrated with wrong length of 50 ohm feedline, or without feedline at all, then smith chart will be rotated by angle depending on difference in length of that feedline, while SWR chart should look the same. for example, if real part of impedance at resonance is too low (ex. 20 ohm), and feedline is quarter wavelength different from what nanovna was calibrated with, then impedance will be still real but too high (ex. 125 ohm), while SWR chart should look the same (1:2.5 SWR minimum) (barring losses in feedline). (this works the same way as quarterwave long feedline impedance matching scheme). for different feedline length differences (non-multiple quarterwave) impedance will be complex at antenna resonance. this problem is avoided by calibrating nanovna with feedline