Outdoor 80m/40m bands "Magnetic loop" antenna.
==>> On every new page FIRST PRESS F5 <<==
Update : 20201031 / 20210115 / 20210816 / 20210822 / 20221131

Just construct it, and it is ready for use.
No matching adjustements needed. Directly perfect match to 50 Ohms using a remotely switched wide band transformer.

(C) The use, publication, copy and modification of al 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.

Please FIRST watch my video presentation :  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 (according to my experiences) the best feeding system at the ONLY good feeding point.
Resulting in a purely H-field radiating, BALANCED antenna and immediately good VSWR.
Wide band matching.

New matchbox PCB is available =>  PCB galery

More space for the series tuning capacitors. 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.

20220331 : 
Especially in the 80m circuit the will run up to 
27A peak RF.
For use with up to 400W peak :

First finish soldering at the top side.
Then :
Solder 2 to 3mm thick wires at the underside of
the transformer PCB. 

Red = blanc copper wire.
Solder in contact with all vias.

Orange = one insulated copper wire.

The schematic of this tuned 1/4 lambda 10m circumference loop with wideband matching transformer, after research by me and  G0CWT.

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.

>> Results of this loop version.
>> General properties of a 1/4 lambda circumference loop.
>> Parts list.
UPDATE 20221204.
>> Setup of the series tuning capacitors on the transformer board. UPDATE 20221131
Newe text and pictures.
>> 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 the above 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 grounding.
-  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 calculated radiation patterns below)
For leakage inductance compensated transformer coupling =>  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.
NO tuner is needed at 80m and 40m.  Perfectly and wideband matched at 40m and 80m.
-  The transformer matching circuit is vastly improved by me, pa0nhc. 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 without problems at 400W SSB.
-  Due to trmy system ansformer leakage induction compensation, =>> 
    when tuned to lowest VSWR,
you are automatically tuned for maximal radiation. <==
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 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.

In a large ABS installation box at the bottom of the loop are the air tuning capacitor, a little 12V DC tuning motor, and a simple to construct 1 : 13.500 mechanical reduction system. 
A smaller ABS box at the top of the loop contains the transformer impedance matching system. 
Both boxes are guarded against condensation by internal 5W heathers.

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 roof).
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.