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Just researching an outdoor long run shortwave antenna. I found some cheap wire online but it said it is resistant to corona discharge:

Will satisfy a wide number of applications related to medical, electronic or electrical equipment which may be operated in environmental conditions where ozone, corona discharge, radiation, heat, weathering or the normally adverse effects of a wide range of oils, solvents, etc., may be encountered.

Would this be suitable or would it block the signal?

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That is a bit of marketing speak that simply means the insulation on the wire will not permit current to flow under some unspecified differential voltage. The insulation is simply black silicone rubber and it is rated for a maximum working voltage of 750 volts.

As an antenna, the silicone rubber insulation will have no practical effect on the efficiency or effectiveness of the antenna. If you are cutting the antenna to some specific length assuming a bare wire, you can take 3% or so off that length to account for the dielectric effect of the insulation.

Unlike many wires insulated with common PVC (e.g. THHN and XHHW), the black silicone rubber should not suffer from UV degradation. So unlike THHN, for example, you won't go out in your garden only to find pieces of insulation lying about. As @MikeWaters points out, the silicone rubber is also generally resistant to ozone which may help to keep the insulation intact if your antenna happens to be exposed to high ozone levels.

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    $\begingroup$ A wire designed to be resistant to corona discharge will also offer some degree of protection against precipitation static (P-static) compared to a bare wire. $\endgroup$ – Cecil - W5DXP Jan 31 '19 at 13:36
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    $\begingroup$ In industrial high voltage switchgear, corona creates ozone. And ozone can deteriorate rubber insulation, which in turn has historically caused catastrophic failures. Note that the wire specs also say that the insulation is resistant to ozone. I think that's the reason it is labeled as such. $\endgroup$ – Mike Waters Jan 31 '19 at 16:19
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    $\begingroup$ @MikeWaters you should put that in an answer. $\endgroup$ – Phil Frost - W8II Jan 31 '19 at 18:06
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    $\begingroup$ @MikeWaters From Wikipedia: "Marketing speak is a related label for wording styles used to promote a product or service to a wide audience by seeking to create the impression that the vendors of the service possess a high level of sophistication, skill, and technical knowledge." $\endgroup$ – Glenn W9IQ Jan 31 '19 at 22:58
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    $\begingroup$ @MikeWaters I am probably more cynical! $\endgroup$ – Glenn W9IQ Feb 1 '19 at 16:15
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In industrial high voltage switchgear, corona creates ozone. And ozone can deteriorate rubber insulation, which in turn has historically caused catastrophic failures. Note that the wire specs also say that the insulation is resistant to ozone. I think that's the reason it is labeled as such.

Regardless, that wire will work just fine as an antenna!

Having said all of this, if you have a loose strand of wire with a sharp end, you can still have a corona discharge and that can cause noise in your receiver. But that's true of ANY kind of stranded wire.

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