Is it beneficial to increase the physical size or number of turns of wire on the cross of the antenna used in a VLF SID Monitoring system?

Generally, the bigger the better within practical limits. Consider its orientation  (N-S or E-W), where it will be located, will it be moved, will the mount support the weight of wire.

One way to think about a loop aerial is its effective area. A single turn of a square aerial 10m by 10m has an area of 100sq m. An aerial 1m square with 100 turns has an area of 100sq m. Similarly, a smaller aerial 0.5m square with 400 turns. A smaller aerial is considerably easier to build and transport. 

At this point John’s point about the wire resistance becomes important, the length of wire increases the resistance and weight of the aerial. being 40m, 400m and 800m,  respectively.

A rule of thumb is increasing the size is more effective than adding more turns. The calculations for aerial impedance can be found in the UKRAA VLF Manual. If you intend to tune the aerial this will assist in calculating the tuning capacitor values.

A loop aerial “works” with the magnetic field of the radio wave and needs to be vertical. 

A 1m aerial with 0.5mm wire works well, from memory this took a full 0.5kg reel of wire.

Andrew Thomas

UKRAA, BAA RAG Mailing List, 18/10/2025.