Since July is now over, here is the solution to the July 2020 WIARC Quiz. The monthly quiz will take a break for August.
This quiz dealt with antenna feed-lines, impedances and SWR. To refresh your memory, he is the scenario:
An amateur radio operator has build a loop antenna for the 20m HF band. Using simulations and confirmation with an antenna analyzer, it has been determined that, at 14.1 MHz, the feed-point impedance (directly at the antenna) is 110 ohm with negligible reactive component (i.e. it is resonant at that frequency). The location of the antenna requires a feed-line length of at least 30 ft (9.1m).
Which of the following feed-line types/length combinations would be most appropriate to feed this antenna without the use of an antenna tuner or trans-match?
The most correct answer is D). A transmission line with an electrical length equal to an odd number of quarter-wavelengths acts as an impedance transformer when there is standing wave, where the input impedance to the line Z1 and load impedance Z2 are such that Z1 x Z2 = Zo^2. So, Z1 = Zo^2 / Z2 = 5625 / 110 = 51 ohms.
Correct answers received: