A common method of feeding a small transmitting loop is to use a small auxiliary input loop. This is sometimes referred to as the “Faraday feed”, implying a shielded feed loop though many so-called shielded loops are not effective (Duffy 2007), but the loop does not need to be shielded nor does there need to be a metallic connection to the main loop.
This article looks at an equivalent circuit. Continue reading Equivalent circuit of small transmitting loop with auxiliary loop feed
One of the feed arrangements used for small transmitting loops (STL) is the so-called gamma match, though it is questionable if these are quite the same as matches of the same name on a linear dipole. Continue reading Small transmitting loop – gamma match
The concept of “additional loss due to VSWR” is so engrained in Ham mythology.
Here it is detailed in the latest version of TLW announced in QST June 2014. On the second last line TLW lists “additional loss due to SWR” as 0.003dB, which seems ok in relative terms as the cable is nominally matched (VSWR=1.03). Continue reading Additional loss due to VSWR – a quite flawed concept
This article describes a linear circuit model for a small transmitting loop with auxiliary loop feed. Continue reading Small transmitting loop – linear circuit analysis
This article describes a NEC-4 model for a small transmitting loop with auxiliary loop feed. Continue reading Small transmitting loop – NEC-4 analysis
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
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