Tuned Loop Antenna
Department and University.
My radio collection;
You can improve your Medium Wave reception with this little
Do-It-Yourself project; you'll spend about 5 guilders on materials
(or use your junkbox) and one evening to build it.
Have fun and be surprised by the result!
The antanna consists of an LC (tuning) circuit formed by the air-core
loop and a tuning condenser.
High-frequent magnetic fields induce currents in the loop, and these
are (passively) amplified by the resonance of the LC circuit for
the frequency to which the circuit is tuned.
The reaction is maximal if the field lines
flow through the core, that is, the axis of the core is perpendicular
to the direction of the transmitter, and minimal if the axis points
in the transmitter direction.
The energy can be guided into your receiver in several ways.
(1) If you use a portable radio with built-in ferrite rod, just place
it inside or near the loop.
(2) You can add a pickup coil, consisting of several windings isolated
from the primary coil, and connect it to the antanna/ground input of
The antenna improves reception of weak or interfered stations in
The antenna principle resembles that of the famous
I am not claiming that you'll have the same performance, but building
your own loop is fun and a lot cheaper!
- Radio signals consist of electic and magnetic waves, and while
a longwire or dipole reacts to electric fields, the loop
reacts to magnetic fields.
Because interference of atmosphere or applications is electric,
it is ignored by the loop.
- The loop is quite directional, and you can pull in a remote
station A that is overshouted by a closer or stronger station B
(on the same or an adjacent channel) by nulling out B.
- The tuning circuit is sufficiently selective to ensure that
the resonance is appreciably stronger for the chosen
frequency than it is for adjacent channels; this is a great
help in reducing Adjacent Channel Interference (ACI).
The wooden frame, constructed from 17x28mm wood in my junkbox,
defines a 50cm x 50cm square on which the primary coil is wound
for 14 turns.
The distance between turns is 1cm, with an exception of turns 7 and 8,
which are 2cm apart to allow placement of the leg.
The total wire length of the primary coil is about 28m (this was the
most expensive part because the wire is 5ct/m!) and its DC resistance
is about 1 Ohm.
The tuning capacitor comes from the junk box.
The secondary loop consists of 4 turns of isolated wire.
I didn't design the antenna for low electric pickup so I do experience
interference from electrical sources.
Electrical pickup can be reduced by shielding the primary loop;
perhaps my next DIY antenna will be shielded...
The selectivity and directionality are nice for MW DX-ing.
Some ascii art
w x x w w = wire wound around frame
w x x w x = wooden x-shape made of two
w x x w 70 cm wooden rods
w x x w L = leg
w x x w P = wooden pig, 18cm long but nearly
w x w invisible because it is in view
w xLx w direction
w x L x w S = stand
w x L x w C = Tuning cap with wire \
w x L x w
w x L x w
wP L Pw
Are you satisfied?
That is great!
Please let me know.
Brett D. Saylor from Pennsylvania reported excellent reception after
building the project.
Gerard Tel, email@example.com