[Lowfer] Worthwhile going to Shielded loop?

[Steve Dove]

Hi Paul,

I use amongst (many) other things here a large shielded single turn loop.

Translated, that means 200' of RG6 with the screens unconnected at the top for the 
necessary 'break', in an upright 'diamond' shape, top at about 70'.  It feeds a differential 
low-input-Z amplifier, which then feeds RG6 back to the shack.

Negatives:  Big mother.  Difficult to get rid of common-mode sensitivity (somewhat prone 
to the 'squirglies')  -  heroic amounts of grounding and commom-mode choking to get it to 
be acceptably quiet.  Not as sensitive or quiet as a 6'-a-side multiturn tuned loop.

Pluses:  Plenty enough signal level.  Requires no tuning.  Just sits there and works, 
except when the transistors in the preamp get nuked.  'Hears' EU 136kHz just fine.

The 'no tuning' no-Q aspect is perfect for its primary application, which is sitting there all 
day and night looking for DCF-39 for the website.  Alan, G3NYK warned me against using 
a hi-Q antenna for this, since if it drifts as they are wont, the sensitivity changes  -  not 
clever for the purpose, and high in operational maintenance.

Out back yonder there is also a smaller (100' circ.) unshielded loop, coupled with a 1:20 
transformer.  This *really* needs an amplifer to be useful.  It hears less garbage but is 
otherwise comparable to the bigger loop (less common-mode issues).

Repeating, however, neither are as good a 'microscope' as a tuned loop.

        Cheers,

                Steve        W3EEE




0/27/2003 5:26:25 PM, "paulc" <paulc@snet.net> wrote:

>Hey Folks,
>
>Got a loop up this weekend.  150' cicumference... if you can call it
>circumference.  The loop is actually more of a diamond with the apex at 50
>feet or so.
>