We decided that we would take advantage of the sunny weather, and set up for some radio fun on the office roof after work. We setup the 1/4 wave ground plane antenna, and double checked the SWR with a nanoVNA. It showed an unexpectedly high value of 1:4. That can’t be right – when we had set up this antenna in the past, we had the SWR closer to 1:1.3. Something was up!
After adjusting the ground plane radials as much as possible, playing with the height at which the radiator sat, we couldn’t improve the SWR enough to confidently transmit. Was it the location? We were fairly close to the metal railings running around the edge of the roof terrace. Perhaps they were interfering with the antenna? We relocated to a spot that we had successfully used before.
After relocating, we still had a too-high SWR. I then decided to cross check the measurements with my NanoVNA, in case the calibration of the nanoVNA was off. To my surprise, the SWR was 1:1.3! Much better! Was it the other nanoVNA? We swapped over, using the SMA to BNC connector from my nanoVNA on my friends one – suddenly he got the same results! Uhoh – the SMA to BNC connector that my friend was using was a bit dodgy, and needed to be fully screwed onto the nanoVNA (so tightly screwed on, that you felt that you would break the connector) in order to make proper measurements!
Next time, we will double check with the second nanoVNA, before going through the hassle of relocating the antenna.
