I have spoken in several recent articles about antennas that exhibit a simple series resonance with constant or near constant R near resonance.
Sometimes the impedance transformation used may hide that simplicity. Continue reading Simple resonators might not appear as such initially
This article explores a generic VSWR curve for simple series resonant matched antennas. Continue reading VSWR curve of a simple series resonant antenna
The ‘net abounds with articles describing easy to build low cost small transmitting loops (STL).
This article describes measurement of a STL for 4MHz using RG213 coaxial cable for the main loop and its tuning capacitance, and a smaller plain wire loop for transformation to 50Ω. Continue reading A QRP small transmitting loop evaluation
There are many calculators for design of small transmitting loops (STL). This article compares one quite old DOS one and a mature popular modern spreadsheet. Continue reading Small transmitting loop calculators – a comparison
The ARRL Antenna Book 21 (Straw 2007) gives equations and advice for design of small transmitting loops.
Many Hams have used these formulas and method for their designs, and some have even produced design tools (online calculators and spreadsheets) implementing these formulas.
This article reviews these formulas and advice. Continue reading ARRL Antenna Book 21 on small transmitting loops
Off centre fed (OCF) dipoles are very popular with Hams on HF.
Many claims are made for variations of the theme, but the essential common feature is that the offset feed point provides a feed point impedance that is not too unsuited to 50Ω coaxial feed line at the fundamental resonance of the dipole and half wave harmonics. Continue reading OCF dipoles
There is a common Rule of Thumb that to be effective, the magnitude of common mode impedance of a Guanella current balun in an antenna system should be at least 500Ω.
This article proposes a possible origin for this thinking, and discusses the validity of the underlying model. Continue reading Baluns – Rule 500
Efficiency and gain of Small Transmitting Loops (STL) referred to an online calculator (Calculate small transmitting loop gain from bandwidth measurement) for estimating the efficiency and gain of an STL.
This article documents an NEC-4 article of a 1m diameter tuned loop of 20mm diameter copper at 7MHz with a driving loop of approximately 0.2m diameter. Continue reading Validation of loop efficiency calculator
One sees simplistic application of ohms law to antenna balun problems frequently in online forums, but is the technique valid? Continue reading Using Ohms law on antenna baluns
Small Transmitting Loops (STL) are loops of less than about 0.1λ in diameter or about 0.3λ in circumference. Below these limits, the current around the loop is almost uniform and this permits a simplified analysis. (A stricter definition of 0.3λ in circumference could be argued.)
These antennas are ascribed all sorts of magic properties, low noise, able to create band openings when conditions are poor etc. Continue reading The magic of small transmitting loops