CAT 5e cable as TV antenna lead in

[wa2ise]

CAT 5e, and CAT 6 cable consists of 4 twisted pairs, each pair 100 ohm balanced. If you parallel two pairs, that becomes 50 ohm balanced. Which would be great for ham radio work, as most ham radio equipment antenna input/outputs are 50 ohm unbalanced. You'd need a 1:1 balum, (where the coax and the balanced lines connect together) which can be done by coiling up 50 ohm coax about 10 turns, the coil measuring about 10 to 15 cm diameter. CAT 5e attenuation (per twisted pair) is 4.4dB @ 50MHz, and 11dB at 250MHz. This would be for VHF, UHF will be more attenuation. If you have a ham radio license, and a 2 meter or 222MHz handi-talkie, you could use this CAT 5e scheme to drive a dipole antenna, with about 20W max. But this is a TV forum. TVs and set top converter boxes expect 75 ohm feeds, so there will be some mismatch with the use of CAT 5e. So we have a choice: use one twisted pair, at 100 ohms to 75 ohms, or a pair of twisted pairs to give us 50 ohm to the 75 ohm input. The attenuation with the use of the two pairs would be half that of just one pair, so the two pair would be a better choice. And dipole antennas have an impedance of 50 ohms anyway (at resonance, will vary a lot off resonance).

Only reason to consider CAT 5e is if you have a ton of it laying around and a lack of normal 75 ohm cable.

[avionic]

Isn't CAT5e unshielded. http://en.wikipedia.org/wiki/Category_5_cable
.Would be very noisy for Amateur Rx / Tx ...SWR would probably be off the chart.TV would not be much better. Just buy the right stuff and be done with it.

[wa2ise]

Originally Posted by avionic

Just buy the right stuff and be done with it.

But what fun is that. In any event, it's twisted pair, so in theory it should not pick up any interference. However, if I were so foolish to try to use 2 paralleled pairs of a CAT 5e cable that had the other 2 pairs in computer service, then the 40 or so dB of isolation specified in the cable specs would be way inadequate...