Re: Is RG-59 ok for feedline?

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From: Mont Pierce (mont@netcom.com)
Date: Fri Sep 29 1995 - 04:37:20 EDT


>
> If it doesn't rain Saturday, I expect to get a loop antenna up on the roof
> of my new residence (with my roommate/landlord's support!). Thank you all
> for your detailed replies to my question about antenna wire. I attended
> the Grayslake hamfest and bought some flexible multi-strand wire of
> unspeakable beauty. This stuff would be great for metal sculpture.
>
> Question: The friend who is helping me has some RG-59 he's willing to
> contribute for feedline. I know that rectangular loops tend to have high
> impedance. Is the use of RG-59 (75 ohms) ok? Someone told me that it
> would cause resistance and heat and would burn out my (beloved) equipment.
> Should I stick with RG-58?

You've just hit on a subject that I also have wondered about.

When I first became a ham, 20 years ago, we always used RG-59 for dipoles
and RG-58 for verticals. If I remember right, a straight dipole is
actually about 72 ohms impedance. Then, as the dipole elements change
angles, the impedance lowers. A Vertical antenna with radials at 90
degrees is actually about 34 ohms impedance.

Until about 3 years ago, I had been away from ham radio. When I got
relicensed and starting buying materials for antennas, everyone I've
talked to always says "use RG-58" for dipoles and verticals...

What gives? I know the rigs we used 20 years ago where almost all tube
rigs with matching plate tuning circuits. Are newer transistor rigs
more sensitive to having 50 ohm coax attached versus 75 ohm coax?

Back to your questions, I don't know what the impedance is for a loop
antenna, I know a folded dipole is a few hundred ohms, and I would use
a 4:1 balun for that.

72,

-- 
Mont Pierce

+-------------------------------------------------------------------------+ | Ham Call: KM6WT Internet: mont@netcom.com | | bands: 80/40/20/15/10/2 | | modes: cw,ssb,fm | +-------------------------------------------------------------------------+


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