A max. performance 40m - (60m) - 80m transmitting loop antenna.
imple and perfect wideband matching, using a remotely switched transformer.
Just construct it, and it is ready for use. No tuner needed.

The use, publication, copy and modification of all info on this site is only permitted for non-commercial purposes, and thereby explicitly mentioning my radio amateur call sign "PA0NHC", as the original writer / designer / photographer /publisher. (C)  

Improved impedance matching.
Youtube video presentation :

English version

201810 : Installing the new match box at the top (current maximum) of the 10m circumference loop. TuningC is at the bottom.
The transformer leakage inductance is compensated.
F(SWR=1:1.0) = F(max. radiation) resulting in top performance.
This is the ONLY good feeding point and best feeding system.
Resulting in a purely H-field radiating BALANCED antenna, no TVI, wide band matching.

>> Results.
>> Sense and NONsense about "a Magloop"
>> Properties of a 1/4 lambda circumference loop.
>> Copper or aluminum loop ?
>> Circular of square shaped loop ?
>> Wrong and correct calculations
for matching a 1/4 lambda circumference loop antenna.
>> Construction and setup of my new matching board.
>>  Parts list.  Update : 20181221
>> The designing of the matching circuit.
>> Construction of the 10m circumference TX loop
>> Installing the 40 / 60 / 80 m all-weather outdoor TXloop.
>> Checking loop calculations using a formula from Helmut Bensch, DL4KCJ.
>> The influence of temperature variations in Common Mode Chokes.

Many thanks to G0CWT for the eye opening, and proven, results from his empirical research.

         Special :
This low-Q, wide band, 10m circumference loop, is developed according data from G0CWT
It has its maximum efficiency (-0.5dB) at 40m, and only a liitle less at 80m. 
It has omni radiation characteristics. 
Installed at low height (1 to 3m) it is a Near Vertical Indent Sky wave antenna, optimal for regional QSOs (up to 300 km).
Installed at 7-10m height above surroundings it has DX possibilities at 40m and 80m.
Perfectly wideband matched at 40m and 80m, using a remotely switched ring core transformer. 
Tested with 10 minutes 100W continues carrier. 
NO tuner is needed at 80m and 40m.

In a large ABS installation box at the bottom of the loop are the air tuning capacitor, a little 12V DC motor, and a simple to construct 1 : 13.500 mechanical reduction system. 

A smaller ABS box at the top of the loop contains the impedance matching system. Both boxes are guarded against condensation by internal 5W heathers.

Schematic of a tuned 1/4 lambda, 10m circumference loop with 7MHz wideband  transformer matching, after research by G0CWT and pa0nhc.

New matching system.

Square loop, circumference 10m.
Cheaply made from copper water tubing
35 / 28 / 22mm.
The copper knees are soldered with standard electronics tin / lead solder, and reinforced by bolting-through.
The insulator plates and the roofing box
are constructed from Trespa.
All hardware stainless steel.
Base: zinc plated satellite dish foot
with 4 concrete tiles of each 8 kg.
Mast and crossbars : painted wood
(better use composite garden materials).
Three pre-stretched polyester guy wires (flags line) connected to the top of the mast :
Two extra guy wires at the ends of the central cross bar, prevent torque to the radiator and
the mast in stormy whether.
It withstanded very strong winds.

        Properties of this loop :
-  Small, only 2.5m square
Omni-directional NVIS radiator for 40 - 60 - 80m.
-  No radials nor ground needed.
-  Installed at low height (loop center at 2.5m up) it radiates predominantly vertical (NVIS), optimal for regional traffic.
-  If installed at 7m height => also useable for DX (see radiation patterns below)
Transformer coupling compensated for leakage inductance  =>  Immediately perfect wide band match on three bands.
-  No ATU  needed. JUST tune the loop for min. VSWR => ready for transmitting with perfect match.
-  Closed, balanced system.
        pure magnetic radiation
        While receiving      : Insensitive for E-filed man-made-noises
        While transmitting  : Minimal chances for BCI/TVI

The grounding and denoising of my antenna system

Download  "loopcalc.exe" with which the properties of small loops (circumference < 1/20 lambda) can be calculated.
Download "MMANA-GAL" antenna modeling software.

Radiation patterns, OMNI DIRECTIONAL.
Calculated with "MMANA-GAL_basic" for specified height of loop center (The tuningC is only 1.75m above the roof surface).

                   NVIS properties at low height on 80m band.             NVIS and DX properties on 40m band when at elevated height.