Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?

Jim Garland 4cx250b at
Sat Jan 2 12:03:26 EST 2016

I did some tests a few years ago on unshielded CAT6  (UTP) cable. The
twisted pairs in the cable are rated at 100 ohm nominal impedance, so I
paralleled two sets of twisted pairs together and measured their VSWR.
Surprisinlgy I found the cable handled 100W at 20m, with negligible VSWR.  I
thought about using the CAT6 for the feedline of portable antennas, but
found that the noise pickup was very high. To do this properly (which I
didn't do in my esperiement)  one would use a simple 1:2
unbalanced-to-balanced balun for a single twisted pair, as well as STP
cable, but I don't see any problems doing so.
Jim W8ZR

> -----Original Message-----
> From: Topband [mailto:topband-bounces at] On Behalf Of PA3CSG
> Sent: Saturday, January 02, 2016 09:53 AM
> To: Topband at
> Subject: Re: Topband: Using shielded CAT5 data cable as feedline for
active antenna;
> benefits of multi-turn K9AY loop/SAL/etc?
> Hi!
> I tried to measure this UTP cable as a receive line. For the results see:
> utp
> The plan is only slowly moving forward:
> To use one twisted pair as a receive line
> One pair as the supply voltage
> One pair to communicate via a RS485 protocol to control a several RX
> antennas / K9AY and to control the gain of the preamp as well.
> One pair left.
> Since the discussion is going this way, how about the above idea?
> I have not tried it but would be interested in your comments.
> Regards & HNY!
> Geert PA3CSG
> Op 02-01-16 om 16:45 schreef Pete Smith N4ZR:
> > I was recently reading a web page by LZ1AQ
> > <>.  It is full of fascinating data and
> > design equations for the use of small magnetic loop antennas.  There
> > were two points, in particular, that caught my layman's attention:
> >
> > 1.  He recommends using shielded CAT5 data cable with RJ-45 connectors
> > as feedline.  The obvious advantage is having three pairs left over
> > for voltage supply and control.  See
> > <> for more information.
> >
> > 2.  He cites experimental data showing that coplanar crossed loops and
> > multi-turn quad loops both offer very significant improvement in the
> > recovered signalcompared with a single loop.  See
> > <>
> > to check whether I got this right. Anyway, it occurred to me to ask if
> > anyone has ever tried multiturn K9AY, SAL or flag/pennant receiving
> > antennas, and did you see something similar?
> >
> > Any other critiques of his design would be appreciated.  The price is
> > certainly right, and the construction looks good. A couple of 1-meter
> > coplanar loops wouldn't be at all hard to construct.
> >
> _________________
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