[TenTec] TWINCOM feedline ?????????????

[Dr. Gerald N. Johnson, electrical engineer]

Incredibly stretched truth. It has much affinity with the solid
byproducts of a male bovine. Any alloy of aluminum has poorer
conductivity than aluminum. Any alloy with lots of titanium will likely
be more resistive than steel, and very expensive. Incredibly lossy
antennas make for beautiful patterns, and very wide SWR bandwidths, but
who needs to go the to work of mounting a dummy load on top the tower
because they have lousy efficiency.

Their claim of 250 ohm for TWINCOM seems to be a little wild also,
judging by the picture of the end. Looks like its closer to 150 or less
with each side being only probably the German standard 60 ohms. Two
coaxes in pushpull doesn't make four times the characteristic Z, it
makes twice.

At Collins for VOA we built 300 ohm balanced shielded lines air spaced.
Each 150 coax used 8" inch irrigation tubing for the outer conductor and
1/2" copper water pipe (5/8" OD). It had to handle a megawatt peak.
Dielectric increases the capacitance and so requires a greater ratio of
outer to inner conductor diameters. The picture of TWINCOM doesn't show
a ratio greater than required for 50 to 60 ohm polyethylene coax. For a
coax with a shield 1/2" diameter, the center conductor would have to be
smaller than 1/32" diameter for air, half that for polyethylene
dielectric, .016" diameter. That's not what is in the picture. Nor is
that a conductor size that will handle 5 KW.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.