Has anyone ever considered using computer ribbon cable to make a broadband
dipole?
On Thu, Apr 18, 2019 at 2:06 PM David Gilbert <xdavid@cis-broadband.com>
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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--
- 73 -
- Joe W6JWP
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