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HB9ABX > TECHNIK 02.06.20 08:23l 36 Lines 1850 Bytes #999 (999) @ WW
BID : 26UDB0FHN02B
Read: GAST
Subj: Magnetic Loop Antenna
Path: DB0FFL<DB0FHN
Sent: 200602/0723z @:DB0FHN.#BAY.DEU.EU [JN59NK Nuernberg] obcm1.07b12 LT:999
From: HB9ABX @ DB0FHN.#BAY.DEU.EU (Felix)
To: TECHNIK @ WW
Reply-To: HB9ABX @ HB9EAS.CHE.EU
X-Info: Sent with login password
Magnetic Loop Antenna
The magnetic loop antenna is an extremly efficient short wave antenna for the
small size it constitutes.
It consists of a loop radiator made of copper or aluminium tubing and a tunable
capacitor.
The size of the antenna is very small as compared to the size of a traditional
antenna as dipole, beam, quad or vertical. The diameter of the loop is in the
range of 1/10 to 1/100 of the wavelength.
The antenna works with the magnetic component of the EM field, which extends to
the both EM components on larger distance. For that reason the antenna operates
well close to ground and radiates a much stronger signal than a dipole when
both are close to ground.
Surely, a full size dipole mounted in its optimal hight radiates better than a
magnetic loop, but due its efficiency at low height the magnetic loop is an
excellent portable antenna or may be used well as indoor antenne when external
antennas are not permitted.
The capacitor of the antenna needs to be remotely adjustable to allow a
frequency tuning range from 1:2 or 1:3. When properly built, the SWR is below
1.1 on the tuned frequency over the full tuning range.
The bandwidth is always very small and covers only a few KHz. The high Q of the
antenna allows a selective receiption and suppresses effectively QRM of nearby
BC stations, as well as other QRM.
Here I am using 2 loop antennas, one for 3.5 to 10 MHz and one for
14 to 30 Mhz, both antennas with only 85cm diameter, below the roof.
The 14 to 30 MHZ antenna with 50 W output allows for regular worldwide contacts
with good results.
The antenna can be built easily as homebrew project if one can find or build a
suitable capacitor.
73, Felix, HB9ABX (felix-abx @ gmx.ch)
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