A correspondent sent me a pic of a commercial balun asking “How does this balun work”. He explained that it is a “combination 1:4 balun followed by a current choke”.
My first thought was that this is likely to have been a creation of Jerry Sevick… but let’s try and analyse it. Continue reading (How) does this balun work?
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
This article documents a series of tests of BLHeli v11.2 damping.
The test configuration is 4S Lipo, HK 9261000003 ESC, HK 4822-690kv motor with 1045SF prop in a static bench test. Note that the ESC uses FET driver chips that deliver quite fast switching. Continue reading BLHeli v11.2 damping evaluation
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
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.
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
The clock used in most Silabs C8051F33x based ESCs is an internal RC clock quoted at 2% accuracy, and 50ppm/° temperature sensitivity. Continue reading ESC oscillator accuracy – Silabs internal oscillator
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