[TowerTalk] KF4BWG

Thu Apr 18 17:06:21 EDT 2019

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
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk