[Lowfer] RE: Worthwhile going to Shielded loop?

[Stewart Nelson]

Hi Alberto and all,

My UTP cable is about 30 meters.

The wire is 24 AWG, DC resistance of 28.6 ohms / 1000 feet
(each conductor).  Capacitance runs about 14 pf / foot.
Found a spec on the net that says 17 pf / foot maximum.
Impedance is nominally 100 ohms.

The lowest frequency for which I could find an attenuation
spec is 4 MHz, where it is 13 dB / 1000 feet.  That would
be 1.07 dB for 25 meters.

The DC loop resistance for 25 meters is 4.7 ohms, which
corresponds to 0.2 dB attenuation if source and load are
100 ohms.

My guess for actual attenuation at 200 kHz is about 0.5 dB.

73,

Stewart KK7KA

----- Original Message ----- 
From: "Alberto di Bene" <dibene@usa.net>
To: <lowfer@mailman.qth.net>
Sent: Thursday, October 30, 2003 11:09 AM
Subject: [Lowfer] RE: Worthwhile going to Shielded loop?


> "Stewart Nelson" <sn@scgroup.com> wrote:
> 
> > 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.  
> > [...]
> 
> Hi Stewart,
>    no laughs at all on this side, on the contrary, I like the idea 
> of using UTP cable instead of coax.... how many meters do you have ?
> In my case I would need at least 25 meters (abt 82 feet). Do you think
> they are too many ? At these frequencies the transmission line effect
> is inexistant, only the capacitance enters into play. And frankly I
> don't know how many pF/meter does each couple of the UTP cable have.
> 
> 73  Alberto  I2PHD