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.

Update :
20201031 / 20210115 / 20210421.
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)  
Many thanks to:
G0CWT for his eye opening results from his empirical research.
K9YC for his much research on Common Mode Chokes.
DL4KCJ for his loaded loop Q calculation formula.

Always first press F5 to reload the latest version from the providers server.

Please see my video presentation first :  TXloop English

201810 : Installing the new match box at the top (current maximum) of the 10m circumference loop.
The tuningC is at the bottom.
This is the ONLY good feeding point and best feeding system.
Resulting in a purely H-field radiating, BALANCED antenna and immediate good VSWR.
Wide band matching.

NEW matching transformer PCB available =>  PCB galery

More space for the series tuning capacitors. Their bottom tracks are interconnected with their top tracks.
Different kinds of capacitors will fit : high current SMD, Mica, film.
The transformer is wound on one 61mm #61 core, maximal power is 400W at 3.5 MHz
The maximal antenna current at 3.5 MHz is then 25A.

For minimal losses, use PURE copper pipe for the loop radiator !


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

New improved 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.

More detailed descriptions :

>> Results of this loop version.
>> General properties of a 1/4 lambda circumference loop.
>>  Parts list.
>> Setup of the series tuning capacitors on the transformer board.
>> The tuning box.
>> Construction of the 10m circumference TX loop.
>> A wooden mast or metal mast ?
>> Installing the 40 / 60 / 80 m all-weather outdoor TXloop.
>> Grounding and de-noising.
>> Optimal 80m and/or 160m versions.

Detailed info.

>> Designing the transformer for the pa0nhc loop.
>> Sense and NONsense about "Magloops".
>> Circular of square shaped loop ?
>> Copper or aluminum loop ? 
>> Wrong and correct calculations for matching a 1/4 lambda circumference loop antenna.
>> Checking these loop calculations using a formula from Helmut Bensch, DL4KCJ.

         Properties :
-  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

This low-Q, wide band, max. performance 10m circumference loop is developed after reading valuable experiences of G0CWT.
-  The matching circuit is vastly improved by me, pa0nhc.
-  This loop
has its maximum efficiency (-0.5dB) at 40m, and only a little less at 80m. 
-  It has omni (non-directional) radiation characteristics. 
-  Installed at low height (1 to 3m) it is an NVIS (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 and wideband matched at 40m and 80m, using a remotely switched ring core transformer. 
-  The matching circuit at the top of the loop is tested with 10 minutes 100W continues carrier and used with 300W SSB.
NO tuner is needed at 80m and 40m. When tuned to min. VSWR always low VSWR < 1:1.2, and maximal radiation.

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.

Download  "loopcalc.exe" with which the properties of small loops (circumference < 1/20 lambda) can be calculated.

Calculated radiation patterns of my 10m circumference loop. 

Calculated with "MMANA-GAL_basic" for specified loop center heights.

"Antenna height" is the height of the CENTER of the loop above "Ground".
(The loop bottom and tuning capacitor are 1.25m closer to the ground).

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