Message-ID: <500EB973.8080005@iup.uni-heidelberg.de>
Date: Tue, 24 Jul 2012 17:04:19 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: Pretests for the 630m band dipole
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MF,

This week i intend to start my tests with a full size dipole for the 
630m band. All the equipment for this /p is available now.

Since the dipole is VERY close to ground (relative to Lambda) there will 
be a capacitive component and the Z=R at resonance will be lower than 36 
Ohm of course.
I have just done some simulations in EZNEC and found that it is useful 
to feed the dipole assymetrical, i.e.  not in the center. The simulation 
tells that a wire length of 315m will be necessary. The resonance 
frequency does not change by different feed points. I hope this applies 
in practice as well :-)
The electrical parameters will depend on the soil conductivity and 
epsilon r, which i don't know exactly of course. But if the settings in 
the simulation are reasonable, then there will be a real component of 
Z=R (=resonance)of 46 Ohm. So i would not even need a transformer to 
match the antenna to the PA.

85% means that one wire is "just" 47m. So if someone lives close to a 
forest, there would be a chance to build such a TX antenna and run the 
major part of the antenna outside the garden. Just a short rest has to 
be inside the own property. For a 90% feed, R would be 96 Ohm. This 
could be matched to 50 Ohm very easily and the shorter part of the 
antenna would only be 31.5m...

I have a bundle of old telephone wire (once found a 1800*0.4mm  x 10m 
length cable) and so i can connect several pieces in series for the 
test. So i can make a table of measurements. The modified MFJ-259B 
antenna analyzer will help, hopefully.
Looking forward to that test.

Due to the permanent number of OP4 listening stations, this mode may 
actually help to get an impression about the efficiency and directivity.

73, Stefan/DK7FC