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 (Reisert 1978).
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
This article uses a report of an experimental small transmitting loop (STL) for 20m to demonstrate application of the calculator Calculate small transmitting loop gain from bandwidth measurement to predict efficiency and gain of the circular STL from the loop radius, conductor radius and measured half power bandwidth. Continue reading Efficiency / gain of a Small Transmitting Loop – a worked example
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.
STL are commonly known by Hams as “magnetic loops”, but that term is rarely used in recognised antenna text books.
The efficiency and free space gain of a circular STL can be easily estimated by calculation from simple measurements. Continue reading Efficiency and gain of Small Transmitting Loops (STL)
At (Bertelsmeier & Magnin 1992) formulas are given for calculating G/T from Sun/ColdSky Y factor in several Ham bands, and solar flux at 10.7cm. Continue reading DJ9BV & F6HYE G/T formula
DJ3JJ wrote up some interesting experiments with Yagis for 432 EME (Haefner 2010). Continue reading DJ3JJ’s 432MHz EME Yagi article in Dubus 1/2010
EMECalc v9.09 was opened, a model for 1296MHz created, and the “get IPS data” button pressed.
The report shows solar flux at 1296MHz to be 106SFU. Continue reading EMECalc v9.09 reconciliation issue