AE7PD documented his measurements of a 3.16m perimeter circular transmitting loop, 1.8m centre height above ground, that he made using 16mm copper tube and a split stator tuning capacitor:
AE7PD gives the radiation efficiency on 20m as 30.5% or -5.2dB.
I present here an alternative analysis of the antenna as measured on 20m.
Assuming the measurements were made with the antenna clear of disturbing conductors etc, and that 5/8″ tube means 16mm OD.
The key measurements were:
- centre frequency 14.165MHz, VSWRmin=1.0;
- VSWR=2.62 bandwidth 22kHz.
A NEC-4.2 model of the antenna at 14MHz was built and calibrated to the measured half power bandwidth (22kHz). Model assumptions include:
- ‘average’ ground (σ=0.005, εr=13);
- Q of the tuning capacitor = 2000;
- conductivity of the loop conductor adjusted to calibrate the model half power bandwidth to measurement.
Note that the model may depart from the actual test scenario in other ways.
Above is the VSWR scan of the calibrated model, the load is matched at centre frequency and half power bandwidth is taken as the range between ReturnLoss=6.99dB points. Continue reading AE7PD’s transmitting loop measurements