[TowerTalk] Polarity question..on a dipole

[Grant Saviers]

I put up some wire electric fence screw in insulators into beach side 
coconut trees for a 160m one 1/4 wl radial on a DXpedition. CW, 1kw.  
They promptly melted and arced over to the screw.  So what works for 
insulating animal fences or DC may not work for RF.  It looked like a 
good insulator but couldn't handle those RF voltages. And I thought 
proven, since after 4 years the same insulators on my 160m T 120' long 
elevated 10' aluminum fence wire radials in the trees look ok (SSB QRO), 
but there are 8 radials so voltage stress is much reduced.

Grant KZ1W



On 3/31/2017 19:25 PM, Patrick Greenlee wrote:
> Farm and Ranch stores like Orchelns, Atwoods, Tractor Supply, etc sell 
> insulating tubing (plastic, don't know composition) for use with 
> electric fencing. It is 1/4 inch or maybe a tad less.  My fence 
> charger is rated for over 200 miles of fence with a fairly high joule 
> rating and puts my digital meter (good for up to 10,000 Volts) into 
> over scale , i.e. has more output than 10KV. I can have a wire 
> insulated with this tubing against grounded pipes or buried in 
> conductive soil and not get arcing to the pipe or the damp conductive 
> dirt.
>
> This stuff might just help stop an antenna from arcing to any part of 
> a tree.  I haven't tried it with antennas as I have no need for that 
> but have used a lot of lot for underground distribution of the hot wire.
>
> Patrick        NJ5G
>
>
> On 3/31/2017 3:39 PM, jimlux wrote:
>> On 3/31/17 12:25 PM, Jim Thomson wrote:
>>> Ok, the peak V on the tips of a dipole is sky high.   But what about 
>>> the polarity between
>>> the ends ?    If one end is + 10 kv, is the other end at – 10 kv  
>>> ??   Is there  a 20 kv
>>> potential difference between them at all times ?
>>>
>>
>> It's very hard to calculate (or measure) the actual voltage at the 
>> ends - best you can say is "it's high".  You can infer a voltage by 
>> calculating the feedpoint impedance of a 1 wavelength long doublet, 
>> then putting in 2x power (each half radiates full power), and using 
>> Ohms law.
>>
>>
>> Yes, it would be opposite polarity.  but not "at all times" because 
>> it goes through zero every half cycle.
>>
>>
>>
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