[Lowfer] RE: Worthwhile going to Shielded loop?

Wed, 29 Oct 2003 20:13:20 +0100

Hi Alberto and all,

Please don't laugh, but my receive loop, ~1.6 meters square, is
connected to the shack via (unshielded) cat-5 cable.
The loop and preamp are balanced, so there is a natural differential
output that drives one cable pair.  At the shack, a transformer
converts to a single ended receiver feed.  A second pair provides
power to the preamp.  One of the remaining four wires is used for
varactor tuning voltage; the others are spares.

The loop Q has been intentionally reduced to about 20, giving a
winter daytime noise level about 10 dB above the preamp noise.
I believe that noise picked up by the unshielded cable is
negligible, more than 20 dB below the preamp noise.

If your loop puts out 6 dB more signal than mine, and the preamp
is 3 or 4 dB quieter, then it will probably be fine untuned.
If you're not sure, be prepared with a suitable remote control
path.

My varactor tuning is marginal with regard to intermod.  If you
have strong interference in the bands of interest, you may need
to use relay-switched capacitors or a motorized variable.  If
strong interference is limited to MF and higher, then it's
probably easier to just put a filter ahead of the preamp.

We are staying "tuned", awaiting your results.

73,

Stewart KK7KA

----- Original Message ----- 
From: "Alberto di Bene" <[email protected]>
To: <[email protected]>
Sent: Wednesday, October 29, 2003 5:19 PM
Subject: [Lowfer] RE: Worthwhile going to Shielded loop?

> Thanks to all who shared their opinions on the subject.
> Most convincing was the argumentation by Stewart Nelson about
> possible phase rotations caused by resonating the loop structure....
> that would in effect preclude experimentations on signalling methods
> where the phase information plays a role.
> 
> Must reconsider my plans... but I have the hardware ready for a square
> loop of more than 2 meters on each side. This, together with a low
> input impedance preamp, should give some guarantee of enough
> signal  strength, even if not tuned.
> 
> TNX
> 73  Alberto  I2PHD
> 
> 
> 
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