In Finnish rural areas the subscriber lines were often made of twin lead cables. This twin lead line is black in color and it is called "Killu" in Finland. The internal part of the wire is iron and the surface is copper. The wires are covered by PE (Polyethylene, dielectric constant 2.3 - 2.4) solid plastic insulator which has good RF characteristics. Killu line is very suitable for RF use in amateur radio. It is very durable and you can get used cables easily free of charge. The cable is still available from some Finnish supliers.

Two types of the cable
MU 2x1.0 FeCu (wire diameter 1.0 mm, wire spacing approx 3.0 mm)
MU 2x1.4 FeCu (wire diameter 1.4 mm, wire spacing approx 3.8 mm)
See the data sheet here

Access network cables for aerial installation, called "Killu"

I measured the RF characterics of these cables. Here are the results:

Transmission line attenuation (both cable types)
Lower HF bands very low per 100 ft (not measurable)
30 MHz approx 1.5 db per 100 ft
100 MHz approx 3 dB per 100 ft

Transmission line impedance
MU 2x1.0 FeCu Z0 = 145 ohms
MU 2x1.4 FeCu Z0 = 130 ohms

Transmission line velocity factor
MU 2x1.0 FeCu VoP =  0.73
MU 2x1.4 FeCu VoP =  0.70

Single wire velocity factor (split single wire with PE insulation in free space)
Velocity factor is approximately 0.93-0.94

13.08.2009 Matti Hohtola OH7SV