HF Antenna Wire

9 strand hard-drawn copper antenna wire (oxidized)

9 strand hard-drawn copper antenna wire (oxidized)

What is better to use for antenna wire: aluminum ground wire, old coax, or stranded #12 or #10 copper?
I have used all successfully, but I wonder about radiation resistance of each at 70' above sandy loam in Alabama. My land slopes about 30' from north to south across 5 acres with dipoles running east to west.

I use double shielded coax for transmission line when operating at high power. I use RG 6 for UHF/VHF and low power HF. The slight mismatch that RG 6 causes is not noticed when I use my antenna analyzer to tune at near ground level (10').

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by: Claude VE2DPE

Yours is a multifaceted question!

First I should tell you that the choice of antenna wire depends on the application. The following must be considered as they all play a part on the resulting performance:

- frequency of operation (overall unsupported span of the antenna wire);
- RF power fed to the antenna;
- acidity or salinity of the air;
- wind;
- ice (not applicable in your area ;)
- stealthiness (not a concern in your case I assume ;)

Now you are asking which of the following antenna wires is best:

- aluminum ground wire
- old coax
- stranded #12 copper
- stranded #10 copper

There is so much to take into consideration that ... to answer your query properly would take a whole book! :)

But I'll try and boil it down.


Resistance vs Impedance

Your concern is: radiation resistance of each dipole at 70' above sandy loam in Alabama.

Just to make sure that we are on the same page ... Please note that there is a difference between:

1- radiation resistance - called feed point impedance - is a function of physical length of antenna at a given frequency, position of the feed point on the antenna, height above ground and ground conductivity (for RF) below. In your case, in Alabama, ground conductivity is considered good on average.

2- ohmic resistance of wire to RF energy at a given frequency and power level is a function of wire size (skin area) and quality of outer skin. Note also that resistance to RF is one of the variables that have to be factored in the overall impedance of an antenna.

3- DC resistance of wire.

Not much has been written on the matter of resistance of wire to RF because of the many factors that have to be taken into consideration. What has been written is too often too theoretical to be of any practical use.


DC Resistance vs Resistance to RF

There is a difference between DC resistance and RF resistance of wire.

For example:

#10 copper wire has a DC resistance of 0.9987 ohms per 1000 ft at 25 degrees Celsius. Therefore a dipole cut for 1.85 MHz would span over 253 feet. It's DC resistance would be

(253/1000) x 0.9987 = 0.2527 ohms (at DC)

However, it's an entirely different matter when applying RF energy to that wire!

RF travels on the "skin" of the wire. It's called the "skin effect" in radio engineering literature. Therefore the quality of the outer skin of the wire becomes important (by the way, there is NO appreciable difference in skin effect between stranded and solid core copper wire).


High Power Operating

Now, because you hinted to it, I suspect that you are looking for the best wire to use at HIGH POWER. High power would indeed be the most demanding scenario for a wire antenna.

At maximum legal power on dipoles for 160 meters to 10 meters, you should use:
- #10 (or bigger)
- use stranded wire because it will resist longer to constant flexing in the wind;
- stranded copper-clad steel (i.e. Davis RF CopperWeld (TM)) for 160 & 80 meters;
- stranded copper-clad steel or stranded hard-drawn copper for 60 - 10 meters;

Regardless of the amount of RF power you intend to submit your antenna to, do not skimp on the quality of the copper-clad steel wire. Use reputable and highly regarded brands of wire manufacturers. Stay away from "no-names" - which could be good enough running barefoot but certainly NOT at maximum legal power.

- The quality of bonding between the steel wire and the copper "skin" as well as the thickness and evenness of the copper layer both have an impact on the durability of the wire antenna. Cheap copper-clad wire is more susceptible to corrosion and breakage than higher quality copper-clad wire.


Guarding Against Corrosion and Oxidization

Unless you live in - or downwind from - a highly industrialized area, air quality in your area should not significantly oxidize the copper surface. Nevertheless, do expect a slow increase of resistance to RF over time because oxidization will slowly occur anyway. The "skin" of the wire will slowly become resistive to RF wanting to travel on it.

However, to guard against deteriorating bare antenna wire from oxidization and corrosion - I would recommend FLEX-WEAVE (TM) by Davis RF as follows (at operating powers of less than 500 watts):

- #12 polyethylene black jacketed - or PVC coated black or green - for centrally supported 160 meter dipole or inverted 'V' antenna;

- #14 polyethylene black jacketed - or PVC coated black or green - for centrally supported 80 meter antenna and other dipoles for 60 meters to 10 meters;

- if the antenna wire will risk rubbing against tree branches, polyethylene (PE) coating is highly recommended.

Forget about any other types of wire (aluminum, galvanized steel, tin-clad aluminum, etc.) as they present much higher resistance (less conducting "skin") to RF than copper.

===

I admit to oversimplifying things quite a bit here. But, like I said earlier, I could write a book on this because there is so much to take into consideration.

I hope this info will be useful to you and to others who read this.

73 de Claude VE2DPE
HamRadioSecrets.com

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73 de VE2DPE
Claude Jollet
7, Rue de la Rive, Notre-Dame-des-Prairies, Québec, Canada J6E 1M9

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