Stefan, Hartmut,

> The here mentioned antennas from Dallas Lankford are mostly Flag arrays
> which are working great down to 0,5MHz! But for 137kHz the gain is to low.

   Yes that is true but even the original K9AY also has very low gain
as it was designed as an 80/160m receive antenna, to use a k9ay on
LF/MF one needs to scale up the dimensions considerably or use two
turns (as F1AFJ did).  The disadvantage of a large loop is that it no
longer has directivity on 80 or 160M. I am working on an experimental
2-turn K9AY with a relay that can be used to short out one turn so
that it can be used on the 80/160 meter bands as a one turn loop or
137/500 as a two turn loop. I have a variable termination (Vactrol)
which is essential for optimum nulls, particularly over a large
frequency range.

   I agree that Dallas Lankford designs are optimized for the MW BC
band .5-1.7MHz, but in theory they should be scalable to lower
frequencies if one take the time to study the designs. There is much
good information on the Lankford site.

   BTW, Tony Preedy G3LNP published an article last year in QST which
had a loop with variable reactance and resistance termination, by
varying the reactance one could adjust the vertical angle of the main
lobe. This could be quite useful for minimizing QRM.  I exchanged
several e-mails with Tony and his concept could readily be scaled for
use on LF/MF. Another advantage of the Preedy design is that the
variable reactance could be in the shack so you don't have to go
outside to the feedpoint to adjust the antenna. I will look for the
article if you are interested.

Vy 73 Warren K2ORS


On Sun, May 13, 2012 at 4:37 PM, Hartmut Wolff <[email protected]> wrote:
> Am 2012-05-13 19:08, schrieb Stefan Schäfer:
>
>> Any ideas, experiance or advice?
>
>
> Stefan,
> your model shows a lot of thermal noise and the gain is very low.
> Outer Ring below 70dBi is not useable.
>
> Attached is a Eznec file with a cardiod antenna I used with good results.
> The additional preamp had about 20dB gain.
>
> The here mentioned antennas from Dallas Lankford are mostly Flag arrays
> which are working great down to 0,5MHz! But for 137kHz the gain is to low.
>
> --
> 73
> Hartmut



-- 
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1