Newbie question regarding max wattage through an antenna?

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LondonPirate
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Newbie question regarding max wattage through an antenna?

Post by LondonPirate » Fri Mar 15, 2019 3:53 pm

I'm interested in building a simple half wave dipole out of copper piping (just for hobby purposes at the moment so nothing that needs to go on top of a block) and was wondering how I'd go about determining the max current rating for it? When working with wire I know you can use ohm's law and work out how much current will go through it. You can then look up different gauges of wire and their pre-determined ratings and go from there.

How does it work with copper piping though? Being hollow and designed to transport water, it's really hard to determine the equivalent 'rating'. I doubt it's much concern at the moment for my plans (I was thinking of putting up something in the region of 30 watts to broadcast to quite a local area in the future) but lets say one day I wanted to run 150 watts and become a 'proper' pirate, would 22 mm tubing be enough to handle it?

Any and all input is very much appreciated!

nrgkits.nz
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Re: Newbie question regarding max wattage through an antenna?

Post by nrgkits.nz » Fri Mar 15, 2019 7:47 pm

It’s not so much about the max current rating as the current (and voltage) is going to be different at different points along the dipole radiators, at the dipole ends it will be all voltage and very little current (high impedance) and at the dipole center almost zero ohms with very high current and almost no voltage (ohms law) - it really comes down to copper thickness and heat generated. Thicker pipes, cable and interconnects are required for higher power. Reflected power will only add to the heat being generated and if you’re power is high enough then solder could start to reflow. Copper pipes of 22mm diameter will be able to handle far more than 150w as radiators on an antenna, I would suggest looking more closely at the cable and interconnects used instead - thicker will handle more power. Don’t use RG58 above 150w it starts to get quite hot, even at 400w RG213 gets warm - that’s your power being lost as heat. If things get too hot they melt. This is why big commercial installations in the kilowatts use thick copper coaxial piping 100mm+ diameter with large EIA flange connectors to deal with the power.

LondonPirate
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Re: Newbie question regarding max wattage through an antenna?

Post by LondonPirate » Sat Mar 16, 2019 7:48 pm

Ah that makes sense. Thank you for your reply, you've cleared a lot up for me!

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