Message-ID: <3B322147.DA381EE0@nephro.uni-kiel.de>
Date: Thu, 21 Jun 2001 18:31:03 +0200
From: "Peter W. Schnoor" <pwsch@nephro.uni-kiel.de>
Organization: Clinic of Nephrology, University of Kiel
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Loop antenna by DF3LP...
References: <29BDD4F529FCD311B631009027357C4E02258788@btss103a.swh.sk>
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Hello Richard,

Gasparik Richard wrote:
 
>         I have build an loop antenna (project of DF3LP). I find that the
> sensitivity of the loop with preamp is very low. DFC39 is normaly 50-60dB
> over S9 on my LW antenna, but with loop antenna it's 30dB less. 

The "gain" of this antenna is approx. -60
dB, approx. 30 dB down compared to my vertical. 
So the simple preamp as described *plus* a
Dual-Gate MosFet in front of my first mixer stage
are sufficient for hearing/seeing reasonable
background noise levels even on "quiet" winter 
mornings.

> I tuned it for the maximu with serial caps. 

Hmm... I remember using *parallel* caps so that the
loop acts as parallel tuned circuit! Do you apply
rigid Flexwell cable or similar for the frame? I
found a significant difference using rugged air
insulated cable compared to thin coax (60 Ohms) of
unknown origin at the same geometry. RG213 or better
are recommended.

Compared to other loop designs the bandwidth is
*broad* and it was difficult tuning the mid 
frequency right on the amateur band by fixed caps.

> Directivity is very good (more than 40dB at
> 90 degrees). It's normal or not ?

Yes, I found more than 50 dB of directivity at
ground wave (!) propagation.

The main goal for building this loop was (i) nulling 
out the LORAN splatter from SYLT as sharp as 
possible and (ii) shielding the E-field as much 
as possible.

73 es gl de DF3LP
Peter