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@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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