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HB9ABX > TECHNIK 01.07.20 18:07l 42 Lines 1920 Bytes #999 (999) @ WW
BID : 17UDB0FHN05U
Read: GUEST DJ6UX DL8SFG DF7EAV OE7FMI
Subj: ABXKOPPEL
Path: DB0FHN
Sent: 200701/1707z @: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
NEW magnic loop FEEDING system: ABXKOPPEL
-----------------------------------------
The existing magnetic loop antenna system suffer under the problem,
that the SWR does not stay contant low over the full frequency range
of the antenna.
When adjusting the SWR on one band to 1:1, the SWR is rising
on other bands.
A new feeding system was developed to keep the SWR below 1.1
over the full frequency range:
Inductive coupling system using a wire loop, which is led close to the
main loop, at the center of the main loop in the length of half the
diameter of the main loop. Then, from both ends leading to the center,
and from there slightly twisted to the output of the 1:1 current balun.
The input of the current balun connects to the 50 Ohm feeding coax.
The wire of this coupling loop is isolated copper wire of 0.6mm diameter
(AWG 22). The diameter may be up to 1mm (AWG 18), but thicker wire is in
no way better.
The advantage of this coupling system is, that the SWR remains below 1.1
over the full frequency range of the antenna! All the other coupling
systems require readjustment if you change to an other frequency band
to obtain minimum SWR.
Important:
The precise adjustment is done at the final installation location.
This is done by lifting or lowering the center point of the coupling loop
where the twisting of the wire begins, by pulling an isolated guy wire
slightly up or down until the SWR is below 1.1.
In free field, the center point is somewhat higher, in a building or
below a roof somewhat lower.
Dimension of ABXKOPPEL for the 3 turn loop of 85cm diameter:
Length of couple loop tightly led aside the main loop: 43cm
Horizontal length: 40cm (2 x 20cm from corner to center)
Length of twisted wires: 12cm (this length is uncritical)
The full description with explaining pictures is found at:
- http://hb9abx.no-ip.biz/loop1-e.htm
best 73, Felix HB9ABX
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