## Sunday, February 13, 2011

### Full Wave Slanted Delta Loop Antenna

The antenna is based on the basic principle of a full wavelength loop antenna. A single wavelength loop remains an efficient and effective antenna.
- Loop antennas provide additional gain over conventional wire type antennas (1.5 db over a dipole).
- A loop is most efficient when its circumference covers the largest surface area (delta, circular or quad shape).
- Loop antennas perform especially well over poor conducting earth like sand and lossy soils.
- Since a loop is a balanced antenna, it requires a balanced feed mechanism (using a 75 Ohm quarter wave coax).
- It has to be fed at a correct place to achieve respective polarisation. A loop is vertically polarised when fed from the side and horizontally polarised when fed from either the top or bottom.
- Loop antennas have less electrostatic noise in your receiver.

SPECIFICATIONS:
The delta loop can be coarsely cut using standard formula of wavelength (300 / Operating base frequency) but the exact formula for a full wavelength (m) delta loop is (299.8 / Operating base frequency) x 1.05 Quarter wave 75 Ohm matching transformer = 75 / Operating base frequency x velocity of the coax.

Calculation for 40m slanted delta loop :
Frequency : 7.020 MHz (for CW and Digimode)
Lambda = (299.8/7.020) x 1.05 = 44.84m of 2.5mm² copper wire
For equilateral triangle = 44.84m / 3 = 14.95m each side
Quarter wave 75 Ohm matching transformer (velocity of 75 Ohm TV coax = 0.85) = (75 / 7.020) x 0.85 = 9.08m of 75 Ohm coax
Operating bandwidth is 300-350 kHz 2:1 SWR with 2.5mm² copper wire

Calculation for 30m slanted delta loop :
Frequency : 10.120 MHz (for CW and Digimode)
Lambda = (299.8/10.120) x 1.05 = 31.10m of 2.5mm² copper wire
For equilateral triangle = 31.10m / 3 = 10.37m each side
Quarter wave 75 Ohm matching transformer (velocity of 75 Ohm TV coax = 0.85) = (75 / 10.120) x 0.85 = 6.30m of 75 Ohm coax
Operating bandwidth is 300-350 kHz 2:1 SWR with 2.5mm² copper wire

Calculation for 80m slanted delta loop :
Frequency : 3.540 MHz (for CW and Digimode)
Lambda = (299.8/3.540) x 1.05 = 84.69m of 1.5mm² copper wire
For equilateral triangle = 84.69m / 3 = 28.23m each side
Quarter wave 75 Ohm matching transformer (velocity of 75 Ohm TV coax = 0.85) = (75 / 3.540) x 0.85 = 18.01m of 75 Ohm coax
Operating bandwidth is 200-300 kHz 2:1 SWR with 1.5mm² copper wire

Installation :
I fed the antenna at upper corner which is fixed at the top of the tower.Direct feeding with 75 Ohm coax at one side and PL259 UHF male connector at the other side. Then UHF Female/Female and PL259 UHF male connector on 50 Ohm coax to the shack.

Opinion / Comments :
Incredible antenna. I am real pleased with its performance. Working DX on 40m and 30m is no more a problem for me ! I put in place a 80m delta loop antenna with same configuration.
Coaxial Cable used for the Quarter wave 75 Ohm matching transformer :
CAVEL 17PAtC/PH Class A (For digital TV connection and satellite system application)

1) Construction
Center Conductor: 1.13+0.01mm Solid Copper
Dielectric: 4.85+0.05mmFoam PE
Shield: Al/PES/Al
Braid Coverage: 35%X16X4X0.12TC+0.005mm
Jacket: 6.80+0.05mm PE
Generic Standard: EN50117-1
Sectional Standard: EN50117-6

2) Characteristics
Impedance: 75+3 Ohm
Capacitance: 50+3pF/km
Velocity of Propagation: 85%
Conductor resistance Max: Inner:16.8 ohms/km
Outer:26 ohms/km
Return Loss: 20dB min (5-2150MHz)