Loops How does height above ground affect mag loop performance?

[ka3jjz]

Here's something on that subject, via SWLing.com

LZ1AQ Evaluates Impact of the Height Above the Ground on Mag Loop Performance

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: Chavd…

swling.com

Mike

 

[vagrant]

Link to the LZ1AQ write-up.

TLDR:
- RX only loop test
- Loop #1 top about 1 meter AGL and Loop #2 top about 4 meters AGL
- He tested 0.1 - 28 MHz
- Author noted, "...it can not be drawn that one antenna has any advantages compared to the other. For several seconds the one antenna is better but then the other one is ahead".

Author's conclusion:
"The two antennas are with identical performance up to 5 MHz. At higher frequencies the wave interference picture around the two loops is not uniform (for this distance between loops) which manifests as unstable difference. This does not leads to marked superior performance of one of the antennas. The higher the frequency the stronger is this effect

Practically we can mount a small vertical wideband loop at any height which is convenient for our local requirements without deteriorating its performance. An invisible loop almost on the ground level can be used with success for those who have a restrictions or inquisitive neighbors".

Basically, one can enjoy using a loop below the height of a fence line and not worry about triggering a problematic neighbor.

 

[ab3a]

To make significant difference, you need at least 1/4 wave above the ground. What LZ1AQ showed is a small fraction of that height for frequencies up to 5 MHz.

To begin to have an effect, the second antenna should have been at least 15 meters in the air. That's not a trivial structure.

However, if you're stuck with building loops at ground level, consider building a K9AY directional loop system.