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ON7YK - (ex)ON1ABO - (ex)ON7CB
C5YK - C5S - (ex)C56YK

On the web since 2001
Belgian / Gambian Radioamateur Station

Loop Antenna calculation and construction .

Calculation formula manual .

For my delta loop antennas , the formula :
30 M , center frequency 10.120 . λ loop = 1005 / 10.120 = 99,308 ft or λ loop 306,3 / 10.120 = 30,02 m .
40 M , Center frequency 7,100 λ loop = 1005 / 7.100 = 141,55 ft or λ loop 306,3 / 7.100 = 43,14 m .
The velocity factor of the antenne wire is not calculated with it in this formula !!!!
My delta loop antennas are not real triangles , the horizontal leg is longer and the side legs shorter . The radiation diagram of my loop antennas change a bit .

Delta Mono loop Antenna for 7 Mhz .

The feedpoint impedance of my full-wave loop is arround 100-120 Ohm with a gain over a dipole of 1.35 dBi . The impedance changed depending on my configuration , orientation, and choice of feedpoint . To feeding this delta loop , I use 1/4 75 Ohm coax stub Rg-11 / Rg-59 and later 50 Ohm coax to the transceiver . Formula for the transformer : 75 Ohm X VF/Freq. , ( VF= velocity factor ) . Using Rg-11A/U- Rg-59B/U Solid polyethylene ! ( VF = 0,66) as impedance transformer .
My calculation for 30 m : 75 x 0,66 / 10.120 = 4,89 m for 40 m : 75 X 0,66 /7.100 = 6,97 m .
Specification Rg-11A/U . Specification Rg-59B/U .
I found the following powerhandeling for those coax cables depend on supplier.

Powerhandeling coax cable RG-11 , Rg-59 . up to 10 Mhz
Power Handling Coax type / Vs Mhz . 1.0 Mhz . 10.0 Mhz .
Rg-11 8000 Watt 2800 Watt
Rg-59 3900 Watt 1100 Watt

The feeding point is important , the distance from the feedpoint to the top should be one quarter wavelength . Whether this feeding point is left or right does not make a difference .
The antenna wire is CQ-532 (AWG 18) . Using a 4:1 balun with a 50 Ohm coax to the transceiver is also a solution. I use the delta loop on different qth's and every time I have to adjust the antenna .

Properties of Coaxial Cable Dielectrics materials . (c = speed of light in a vacuum)
Dielectric Type . Time Delay
(ns/ft) .		 Propagation
Velocity Factor .
Solid Polyethylene (PE) 1.54 0.659c
Foam Polyethylene (FE) 1.27 0.800c
Foam Polystyrene (FS) 1.12 0.910c
Air Space Polyethylene (ASP) 1.15-1.21 0.840c-0.880c
Solid Teflon (ST) 1.46 0.694c
Air Space Teflon (AST) 1.13-1.20 0.850c-0.900c
40 m Delta loop

40 m Delta loop

Loop Calculator without velocity factor of the antenne wire .

With this calculator you calculate the lengths needed to construct loop antennas . All you need to do is enter the desired resonant (center) frequency in the form below, then click "Calculate Length". The correct lengths for the loops models will be displayed in the chart . This calculator is for HF antennas between 1.8 - 30 mHz .

I take always a bit longer length , better to long than to short !
Enter primary operating frequency in Mhz .


Click to or

Quad Loop.
Full One-Wavelength Loop .
Over level ground, the minimum height for the top corners of the quad loop is the length of one side plus the height of the bottom support posts. Quad loops are most fed in the center of the bottom, horizontal leg.
Each Side .
Feedpoint Distance from Bottom Corner .
Parasitic Delta Loop .
Full One-Wavelength Loop .
Over level ground, the minimum mounting height for the apex of a Delta Loop is the altitude plus the height of the support posts. If the loop is an equilateral triangle as shown, the Minimum Horizontal Spread = the length of one side plus the distance to the tie off points (support posts).
Each Side.
Feedpoint Distance from Apex .
Feedpoint Distance from Bottom Corner .
Minimum Vertical Height .

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