Many thanks to SWLing Post contributor, Harald Kuhl (DL1AX), who shares the following article on LZ1AQ’s website:
Published on: 2018/11/20, Rev. 1.0 July 2018, Rev. 1.1 Nov 2018
Author: Chavdar Levkov LZ1AQ
Two identical small loops were placed one above the other according to Fig.1. One of the loops is very low – almost on the ground. The other one is placed at height which usually is used by the loop users. Two AAA-1C wideband active antenna amplifiers were used. Their gain difference was not more than 0.3 dB. The feeder was FTP cable each 20 m long. No cable baluns were used. The outputs were connected through two way antenna switch to a SD RX (Perseus). I used a measurement technique described in – A Periodic Switching Technique to Compare Receiving Antenna Performance in the Presence of Strong Fading. This is a precise method to compare two receiving antennas with real sky wave signals and the resolution can be less than a decibel. The idea is to switch periodically between two antennas and to estimate their difference on a calibrated graphic strength meter of a SD radio.[…]
I’ve often assumed height had little effect on the performance of an HF loop antenna–this evaluation seems to support that theory. Thanks for sharing this, Harald!