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Date: Tue, 16 Aug 2011 22:36:24 +0200
From: =?UTF-8?B?U3RlZmFuIFNjaMOkZmVy?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Ferrite RX antennas
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Jim, LF,

I'll try to go on as fast as the distributor and ebay did ;-) So this is 
the current situation:

Decided to use the 2x7 bundle. The cross section area of 7 pcs. just 
lokks better :-) Also the complete stick is much more handy and robust.

Markus/DF6NM gave me the hint to overlap the inner rod by 50%. So i 
intentionally broke one rod and put the 2 halfs to the inner ends. One 
complete one is now in the inner center.

See: http://dl.dropbox.com/u/19882028/LF/ferrite%20antenna%20parts.JPG

I took a simple bonding tape to isolate the rods from each other. The 
whole arrangement was fixed by bonding tape and put into a stable and 
very proper PVC tube with 2.5 mm thickness, making the rod very robust 
and give some distance between winding and ferrite (just as in the magic 
antenna article ;-) ).

Ther was even some place to add a bit of that transport foil with the 
air bubbles inside, you know ;-) Perhaps this will be some kind of shock 
protection (hopefully never needed) and fixed the rods inside the tube.

http://dl.dropbox.com/u/19882028/LF/inside.JPG

Now the outer dimensiona are 285 mm x 33 mm.

As a first test i wound a simple wire arround the rod, 22 turns. 
Resonance C is 11.2 nF and f res = 137,1 kHz. Q = 100 (unloaded). During 
the measurement i was irritated by a strange peak near 137.7 kHz which 
was my own transmission during that time ;-)
So L must be 120 uH. Not so much...

Will go on now using the Litz wire and start with about 40 turns and see 
what comes out. Then i go for 60 turns, maybe 80 if Q is still rising.

73, Stefan/DK7FC


Am 16.08.2011 19:01, schrieb James Moritz:
> Dear Stefan, LF Group,
>
>
> ----- Original Message -----
>> The 20 mV is the peak level (thus mVp ;-) ) while the mentioned 100 
>> uV is rms.
>
> OK - so that makes your RX noise level 3dB lower, and gives you 3dB 
> more margin, which is good!
>
> Cheers, Jim Moritz
> 73 de M0BMU