Antenna Design
Antenna Design Software
Loop Antennas ...

Multi-Turn, Square, Frame (or Loop) Receiving Aerials

Author: R.J.Edwards G4FGQ © 17th December 1997

Given the length of one side of the frame, number of turns of wire, the wire diameter and ratio of winding pitch to wire diameter; this program computes inductance, wire RF loss resistance, quality-factor Q, and other results of interest. Stray shunt capacitance is computed and the setting of the variable tuning capacitor is shown for a given resonant frequency.

The loop receiving sensitivity with respect to a highly efficient antenna such as a 1/4-wave vertical is shown in decibels. The impedance across the tuned loop at resonance is computed. This will be of interest when connecting the loop directly to the input of an field effect transistor (FET) head-amplifier. The lower impedance presented to the receiver input by a single turn of wire closely coupled to the main loop is also given. This single-turn alternatively may be connected to the receiver via a short line, with its lower impedance being more closely matched to Z-input of a junction transistor.

It will be seen that loop's stray capacitance increases rapidly as winding pitch decreases for the same diameter wire. This not only limits tuning range of the loop. It also reduces Q and efficiency. The effect is large with only two or three close-wound turns, but is very small, of course, with a single turn. However, the ratio of the winding pitch to the wire diameter can be made too large.

Further Notes
When the width of a single-layer winding is greater than roughly 1/5th of one side of the frame the program becomes less accurate in calculating the winding inductance. However, before this occurs, any wide spacing has probably been overdone and a more efficient loop could result from fewer more closely spaced turns of heavier-gauge wire. A reminder is displayed when the 1/5th point has been passed.

In most cases the dimensions and number of turns for operation over a given band of frequencies will be decided by the type, size and availability of the tuning capacitor. RF loss due to the tuning capacitor is always negligible. When the aerial is impedance-matched to a receiver, its Q and frequency selectivity will be halved by receiver loading.

The computed results apply approximately to loops of other regular shapes such as hexagons and circles which enclose the same areas or that have the same perimeters as a square. Triangles and rectangles are usefully, but are only roughly approximated.

All program input values are entered on the bottom menu line. Incorrect characters are ignored. Either upper or lower-case letters are accepted. When numerical data is expected, any other types of characters, or errors such as a comma instead of of a decimal point, cause the program to abort. If stuck in the Windows DOS Box, try typing "exit (Enter)".

Run this Program from the Web or Download and Run it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link rjeLoop3 then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.

Discuss, debate and ask questions about multi-turn, square, frame (or loop) receiving antennas in the Ham Radio Forum.


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