ARRL Antenna Book 21 on small transmitting loops

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

OCF dipoles

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

TLW v3.24 checkout

I am often asked for recommendations for a replacement for TLLC (Duffy 2001).

The announcement of an update to TLW by ARRL / N6BV in June 2014 QST flagged a possibility.

Screenshot - 13_05_2014 , 15_58_04

Reviewing the available cable types, Belded 8215 (RG-6/U type) was tested for loss with a 75+j0Ω load (approximately a matched load) at 1MHz, and the result of1.147dB does not reconcile with the Belden datasheet showing 1.3124dB, an error of -13%. Continue reading TLW v3.24 checkout

Validation of loop efficiency calculator

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

The magic of small transmitting loops

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

Efficiency / gain of a Small Transmitting Loop – a worked example

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

Efficiency and gain of Small Transmitting Loops (STL)

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)

What does an Antenna Tuning Unit (ATU) do?

An Antenna Tuning Unit (ATU) performs a simple but important function in many transmitting systems.

Almost all things called an ATU are simply impedance transformers, and almost always, narrow band impedance transformers (meaning that when adjusted, they achieved the desired transformation over only a narrow frequency range).

Screenshot - 03_05_2014 , 15_06_33

ATUs come in a range of configurations, each designed for a specific set of characteristics. Above is the heart of a Palstar AT2K T Tuner, just three real passive components that are fully explained by conventional linear circuit theory. Continue reading What does an Antenna Tuning Unit (ATU) do?