Minimum wire gauge for homebrew dipole?

[PrimeNumber]

The title says almost all: what's the minimum wire gauge for a homebrew dipole, for a rig running legal power levels? I want to make an ultralight dipole to take on camping trips, and I'm wondering how small I can get away with using.

I've got a giant spool of 22 AWG laying around. Too small?

 

[SpectreOZ]

Pretty much what ever you land your hands on, when I was 17 I built a wire dipole antenna using single core bell wire and it worked well even chased some DX on 35LSB.

Thinking in terms of durability though I'd definitely opt for some stranded copper wire

 

[jackj]

Anything that will carry the current will work. I wouldn't use 22ga wire to construct a dipole to be fed by a 2 kw transmitter but it should work well for anything up to around 50 watts. Two things to keep in mind are that you need something strong enough to support its own weight without stretching much and smaller wire has a higher resistance.

The skin effect becomes important at RF frequencies. The current is concentrated on the surface of the wire at high frequencies which increases the effective resistance of the antenna. Stranded wire has a much higher surface area than the same gauge solid wire. The more strands in a given size wire, the more surface area. That's why most antenna wire is made up of small size strands.

If you are make an antenna for HF frequencies then I wouldn't use anything smaller than number 16 for frequencies over 20 MHz or 14 for under 20 MHz.

 

[jhooten]

Fed with even small coax like RG58 22 gay may not be self supporting but it will handle the power of a legal cb. I have used 24ga phone wire fed with a short run of RG174 with some success for a temp cb antenna.

 

[PrimeNumber]

The skin effect becomes important at RF frequencies. The current is concentrated on the surface of the wire at high frequencies which increases the effective resistance of the antenna..

That's it! Thanks Jack.

(digs around over at Wikipedia's articles on skin depth and AWG for a few minutes...)

OK, at 30 MHz the skin depth of copper is about 0.02mm, and 22 AWG wire is 0.644mm. That's more than a factor of 30. Looks like we're good to go.

Many thanks for all replies

 

[LtDoc]

The minimum size of wire for any dipole antenna is the one that will support it's own weight and a little bit more if it has to support the feed line too. That minimum size isn't just for dipole antennas but for any that have to support their own weight. It's a mechanical thing, not electrical. The 'surface area' thingy is a matter of size in relation to frequency of use. In the VHF/UHF regions it's certainly possible to use a diameter of conductor that will be beneficial to some extent. At lower than VHF frequencies that size relation to frequency can get very large very quickly. At 10 meters a 3 inch diameter conductor may have some slight benefit. At 80 meters that 3 inchs will turn into something like three feet in diameter to have any benefit at all. There is no noticeable difference between a 18 gauge and 8 gauge wire at 80 meters. There's a way of figuring it if you want to, it's in the ARRL's HandBook.
- 'Doc

 

[KC8ESL]

Part number 534
The WireMan - Antenna Wire

26 AWG - Break strength is 25Lbs. If you can hoist the center of the dipole into the air and support it, you would be fine with this stuff. 4 Watts AM and 12 Watts SSB (1kHz tone for 1 hour), it will never warm up even on a hot day.

 

[TheSpaceMan]

I once used tiny transformer wire taped to plastic clothes line cord, and it worked fine!