There are a host of design tools for Small Transmitting Loops, spreadsheets, online calculators and conventional applications you download and run on your PC. Almost all ignore capacitor loss… and I say almost so that I am not wrong, I have never seen one of these tools that does include capacitor loss. NEC study of … Continue reading On ignoring capacitor losses in Small Transmitting Loops
Recent comments elsewhere on the shape of the plot of measured Q from (Austin et al 2014) gave reason to explore the behaviour of Q for a ‘good’ Small Transmitting Loop (STL) using an NEC-4.2 model. The term Small Transmitting Loop means a loop sufficiently small that there is not a significant departure from smaller … Continue reading NEC study of Small Transmitting Loop Q vs frequency
K4PP described his Small Transmitting Loop (STL), including details of its construction and measured VSWR response. The loop is a 1m diameter circle of 12.7mm dia copper tube with a high Q vacuum cap for tuning. Using a quality capacitor and copper tube, this loop should be as efficient as they come for its size … Continue reading K4PP’s 1m Small Transmitting Loop
(Austin et al 2014) made measurements of feed point impedance of a small transmitting loop using a calibrated transformer, and discussed the loss mechanisms. They also extrapolated their measured data to a larger conductor. This article is an update of my article of 05/02/2015 which contained some errors as a result of my incorrect interpretation … Continue reading Review of Austin et al paper “Loss mechanisms in the electrically small loop antenna”
I mentioned in An NEC-4.2 model of VK5BR’s 1m square loop for 20m that Butler’s ~1m square loop was too large to be considered strictly a Small Transmitting Loop (STL): Note that the loop is sufficiently large that the current is not uniform around the loop (Butler 1991) gives a design for a Small Transmitting … Continue reading Dipole mode component of VK5BR’s 1m square loop for 20m
(Revised 12/11/2015) Small Transmitting Loops (STL) are loops with approximately uniform current around the loop. (King 1969) gives us expressions for an equivalent circuit of the ‘loop mode’ and ‘dipole mode’, it consists of parallel branches for each mode of series R and X: R0: radiation resistance of loop mode; X0: reactance of loop mode; … Continue reading Dipole mode of Small Transmitting Loop per King
In Calculation of equivalent self capacitance of Small Transmitting Loop I mentioned that (Straw 2007), The ARRL Antenna Book 21, gave an expression for equivalent self capacitance of a Small Transmitting Loop of one turn: C=HD where C is in pF, D in cm, and H comes from a given table of length/diameter ratios from … Continue reading Calculation of equivalent self capacitance of Small Transmitting Loop – ARRL
Small Transmitting Loops behave fairly much like an ideal inductance in series with some small resistance. They do however exhibit a self resonance at a frequency where the perimeter is approximately a half wavelength. This can be expected to slightly alter the Xl vs frequency characteristic below the self resonant frequency (SRF), more so as … Continue reading Calculation of equivalent self capacitance of Small Transmitting Loop
(Butler 1991) gives a design for a Small Transmitting Loop (STL) for 14MHz and some other bands. He gives key design data: Tube Diameter d 0.75 inch Circumference S 12.7 feet Area A = 10 square feet Frequency f = 14.2MHz Power P 100 watts Radiation Resistance Rr = 0.137 ohm … Continue reading An NEC-4.2 model of VK5BR’s 1m square loop for 20m
The meaning of the terms efficiency and radiation resistance are often critical to understanding written work on antennas, yet different authors use them differently, often without declaring their intended meaning. Mike Underhill (G3LHZ) is an enthusiastic proponent of Small Transmitting Loops and in his slide presentation (Underhill 2006) challenges the proposition that their efficiency is … Continue reading Underhill on Small Transmitting Loop efficiency