In a message dated 30/01/05 01:32:53 GMT Standard Time, [EMAIL PROTECTED] writes:
All of the 75 ohm stuff that I've seen wasn't rated for high voltages anyway, so it's likely to melt at the voltage loop when hit with high power. AT the very least, it'll be rather lossy. --------------------------------------- There is more robust USA sourced 1kW rated 75 ohm twin available in the market though sadly not as easy to obtain now as in the past. Believe red/black power cable makes an effective 75 ohm twin feeder and this is available for quite high currents though not with high voltages. Am using commercial 75 ohm twin feeder cable rated at 300W at present which is very adequate for the 100W maximum I use. In any case we have in the UK a maximum license power of 400W pep which restricts our exposure to high power effects. Guess would be rather different in the USA with your maximum of 2kW pep. QRO can have it's downside! Not sure that the statement that it would be rather lossy is correct as I have been led to believe that twin feeder is less lossy than coax and particularly the 50 ohm version. Even the 75 ohm hard-line coax as used by cable TV companies was always better than the 50 ohm coax in the loss figures for a given diameter cable. I do use a resonant 1/2 wave trap dipole on 40/80m only at present with the feeder cut to the length recommended by the antenna designer of 70 ft (or multiples of this). Working towards adding a two extra pairs of traps for 80/20 to give added bands of 160m and 20m. With always using resonant antennas the problems that could arise on the twin feeder are minimised and hopefully any interference problems as a result. So far telephones seem the only problem area. The wider spaced twin feeder would be impossible in my case as the operating position is on the opposite side of the room from the window and built into a fitted wardrobe. At a previous house the shack was just that, a wood hut under the centre of the dipole and wide spaced twin feeder came direct to a balanced ATU. As always it is a matter of "cutting the cloth to suit your circumstances". What will be suitable for one situation may be hostile in another. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
