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AW: Problems with Wimo 70cm Helix



Hi Luc

I use this antenna since longtime. Jus after reading your Mail, I, went to control my SWR and found that the SWR is rising from 1.2 to 7 measured with the build in meter of a Icom IC475.

After connecting the Daiwa NS-4663PA SWR meter in the shack, the readings were as bad with the rig's SWR meter, but the Daiwa showed following readings:

430.0 1.1
431.0 1.2
432.0 1.25
433.0 1.28
434.0 1.2
435.0 1.1
436.0 1.2
437.0 1.3
438.0 1.45
439.0 1.45
440.0 1.3

Not too bad I would say, even when we include the line damping of 3dB, the worst true SWR at the antenna is 2.

That is the first part of my story. Once a while, I've measured even with my Daiwa, a real bad SWR. Together with other works at the antennas, I downed the 70 cm Crossyagi and found water in the matching housing of the feeder Loopdipol. After a short investigation I concluded, that the water is entering trough the fastening screw. Wimo made a hole in the tube of the Loop and water entered this hole went trough the tube into the housing. As I move my antennas in Azimuth and Elevation, the pick up of water is pronounced. In the housing is some sort of foam to hold the parts together. This foam acted as sponge for the water.

I've let the Loop dry out really well. Then I sealed all the possible holes with silicone. I even tried to fill the inner parts of the tube with silicone. When i consider the moist weather in Switzerland I've succeeded with my efforts, when I may trust the Daiwa.

Hope this helps and hope that the weather in LX land is better than ours..

73 de Paul HB9OMQ


-----Ursprüngliche Nachricht-----
Von:	Luc Langehegermann [SMTP:lx2gt@qsl.net]
Gesendet am:	Mittwoch, 7. August 2002 20:57
An:	amsat-bb@amsat.org
Betreff:	[amsat-bb] Problems with Wimo 70cm Helix

Hello,

Since a few month's I use here an helix antenna from Wimo, but am not really 
happy with it. Matching is ok at about 433MHz, but it seems impossible to get 
an raisonnable matching around 435. Does anyone know this design and maybe 
has a hint how to tune this antenna. I must admit that even generally I do 
not know how to time helix antennas.

BTW, it is the large model, 70/2.

Thanks, Luc

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