[TowerTalk] KF4BWG

Thu Apr 18 19:30:36 EDT 2019

I do have a question for the experts about what I posted below. What 
effect, if any, is there on skin effect for individual wires when you 
have several in close proximity?  Since skin effect is a field-related 
phenomenon, does having multiple fields in phase mitigate the effect on 
the individual wires?

Just double checking ...

73,
Dave   AB7E

On 4/18/2019 2:06 PM, David Gilbert wrote:
>
> I had no idea the wires could be that thin, but I checked around 
> online and saw horse fence tape with wire thicknesses ranging from 6 
> mils to 12 mils for 15 strand tape, so 7 mils (0.1778 mm) for 18 wires 
> sounds like a good ballpark figure.
>
> You make a great point about the ferromagnetic effect on skin depth.  
> I found this calculator for skin depth:
>
> https://chemandy.com/calculators/round-wire-ac-resistance-calculator.htm
>
> The calculator only has a few typical metals in its menu.  The closest 
> I could get to stainless steel was nickel, so I used that to get an AC 
> resistance of 43 ohms per meter per wire at 3.5 MHz. Dividing by 18 
> for the number of wires gives about 2.4 ohms per meter compared to 
> about 0.1 ohm per meter for a single strand of 14 gauge copper ... 
> using the skin effect calculator in both cases.
>
> Stainless steel would be even worse since it has higher relative 
> permeability than nickel and the formula for skin depth is 
> proportional to the square root of the inverse of permeability. Taking 
> midpoint values for the range of permeabilities shown in various 
> tables the actual number for the horse fence tape with 18 strands of 7 
> mil stainless steel would probably be closer to 5 ohms per meter.
>
> I then generated a model for a 75m Inverted-V in EZNEC+ with an apex 
> at 50 feet, both with and without a 5 ohm load roughly every meter of 
> length.  Radiated power is a function of current so used a 1 amp 
> forcing current in both cases.  Without the five ohm loads it took 46 
> watts to get 1 amp at the feedpoint.  With the 5 ohm loads it took 141 
> watts to get the same 1 amp feedpoint current. That's a power ratio of 
> roughly 3, meaning that the horse fence antenna loses roughly 2 thirds 
> of its power to resistivity loss in the thin stainless steel wires.
>
> By the way, the feedpoint impedance appears to be about 140 ohms at 
> resonance so it's no surprise that KF4BWG used an antenna tuner in his 
> videos.
>
> If anyone spots any errors I've made here please point them out to the 
> list.  The last thing I want to do is spread bad information, but this 
> doesn't look to me like a very efficient antenna.
>
> 73,
> Dave   AB7E
>
>
>
> On 4/18/2019 11:18 AM, Grant Saviers wrote:
>> The wires can be 0.007" diameter.  Not only is the DC resistance 
>> higher for stainless, but the ferromagnetic loss at RF can be 
>> significant.
>>
>> https://www.statelinetack.com/item/field-guardian-2in-polytape-classic-14-wire/BXC33/?srccode=GPSLT&gclid=Cj0KCQjwwODlBRDuARIsAMy_28UA2BShpSxPs83FvSIvuOjQW1dQFVyMhvXhgK7CQK05EtlHaYD0YFYaAgg7EALw_wcB 
>>
>>
>> Grant KZ1W
>>
>> On 4/17/2019 15:42 PM, David Gilbert wrote:
>>>
>>> I'm curious what anyone thinks is unique about this antenna. Yes, it 
>>> is a bit wider than wire and it appears to roll up easily for 
>>> changing lengths, but fundamentally it's just an Inverted-V.  I 
>>> think it's kind of ridiculous that he advertises it as having "more 
>>> gain".  As far as loss in the stainless steel conductor is 
>>> concerned, the 18 wires might offset the higher resistance depending 
>>> upon how thick the wires actually are, but who knows.
>>>
>>> If he's still active, his QRZ.com web page says he's on 3976 Khz 
>>> every morning at 7:45 Tennessee time so WP3C might check there.
>>>
>>> 73, Dave  AB7E
>>>
>>>
>>> On 4/17/2019 1:59 PM, john at kk9a.com wrote:
>>>> I am curious about this product. It appears that these Horse Fence 
>>>> antennas use a wide stainless steel mesh radiator. Since the 
>>>> conductivity of stainless steel is significantly less than copper 
>>>> which is typically used in dipoles, how does this material effect 
>>>> the efficiency?
>>>>
>>>> John KK9A
>>>>
>>>>
>>>> wp3c wrote:
>>>>
>>>>
>>>> HiDid someone knows or known KF4BWG the creator of the Horse Fence 
>>>> antennas?I visited his website and sent some emails but didn’t 
>>>> receive any answer. I’m curious about the broadband of those 
>>>> antennas. If someone knows about that please let me know. 
>>>> ThanksAlfredo WP3C Sent from my T-Mobile 4G LTE Device
>>>>
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