-----Original Message-----
From: k8bhz@hughes.net
Sent: Friday, December 19, 2014 1:34 PM
To: Bill Wichers
Subject: Re: Topband: Confusion in ON4UN's Low Band DXing radial
lengthcalculations.
I fail to see what we're missing here. ALL measurements I quoted were
measured on an MFJ analyzer, not a DC ohmmeter. The "reactive properties" of
the wire are exactly what I measured. Also, the AC (rf) resistance went up
when the radial was placed in the ground. So, we're in agreement on all
points.....
Brian K8BHZ
-----Original Message-----
From: Bill Wichers
Sent: Friday, December 19, 2014 1:11 PM
To: k8bhz@hughes.net ; Tree ; topband@contesting.com
Subject: RE: Topband: Confusion in ON4UN's Low Band DXing radial
lengthcalculations.
What you're missing is that a conductor carrying an *alternating* current,
like RF, also has reactance. Reactance is influenced by capacitance and
inductance. The earth, being essentially somewhere between a lossy conductor
and a lossy dielectric, can influence the electrical properties of the wire.
Velocity factor is influenced by properties of the dielectric. Notice how
there are feedlines that are the same impedance, and have the same outside
diameter but one has a foamed PE dielectric and the other solid (like RG8
and RG213)? The velocity factor is higher in the foamed dielectric. The
electrical length of such cables will be different even though the only
physical differences are the differing dielectric materials and slightly
different gauges of the center conductors.
A "radial" is actually more complex than just a piece of wire on the ground
with resistance. It doesn't lose it's length, but the reactive properties of
the wire (or any wire for that matter) will change as that wire is either
bent, or brought into close proximity with other wires or dielectric
materials. Remember that an inductor is also just a piece of wire with
resistance, but when that wire is coiled it acts as an inductor more than
just a simple piece of wire.
There are also the other reasons for resonant length being less important
with radials (many in parallel, etc.) when they're on the ground that have
been discussed many times in the past. The DC resistance of the radial
itself does not change when brought near the ground, but the AC properties
of the wire do.
-Bill KB8WYP
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of
k8bhz@hughes.net
Sent: Friday, December 19, 2014 12:21 PM
To: Tree; topband@contesting.com
Subject: Re: Topband: Confusion in ON4UN's Low Band DXing radial length
calculations.
I can’t agree with this “conventional” thinking. Why does a piece of wire
magically lose it’s length just because you lay it on the ground? The
electrical
length changes because of Vf, and it’s resistance changes because of the
lossy ground, but it’s still a piece of wire. I’m going to try to attach a
posting I
did back in 2006. If it doesn’t work, I will follow with a separate
posting.
Brian K8BHZ
From: Tree
Sent: Friday, December 19, 2014 10:07 AM
To: Doug Turnbull
Cc: k8bhz@hughes.net ; 160
Subject: Re: Topband: Confusion in ON4UN's Low Band DXing radial length
calculations.
Radials on the ground do not have a magic length. Worrying about
resonance
for them is not necessary.
If you tune a quarter wave wire up in the air - then lay it onto the
ground - it
couples to the ground and is no longer a distinct single piece of wire.
Just
make them an easy length to deal with and put as many of them down as
you can.
Tree N6TR
On Fri, Dec 19, 2014 at 2:28 AM, Doug Turnbull <turnbull@net1.ie> wrote:
Brian,
I understand that the VF varies with soil type. One could just
compensate by being conservative but who wants to use 30/40% more wire
than
needed. Why does the ON4UN book ignore VF when doing the example
problems?
Should I shorten to take into account VF?
73 Doug EI2CN
-----Original Message-----
From: k8bhz@hughes.net [mailto:k8bhz@hughes.net]
Sent: 19 December 2014 00:08
To: Doug Turnbull; Topband@contesting.com
Subject: Re: Topband: Confusion in ON4UN's Low Band DXing radial
lengthcalculations.
Hello Doug,
The 50-60% figure depends on your soil conditions, so may vary quite a
bit.
With my poor, sandy soil, the Vf is 67.7% with the radials laying on the
ground. When I buried them 6", the Vf was 39.8%. Using these shortened
radials, there wasn't much improvement going beyond 16 radials.
To find out your soil conditions, simply lay a temporary dipole on the
ground and use an analyzer to find it's resonance. Then trim to length.
Now
you have your first two radials!
Good luck
Brian K8BHZ
-----Original Message-----
From: Doug Turnbull
Sent: Thursday, December 18, 2014 4:18 PM
To: topband@contesting.com
Subject: Topband: Confusion in ON4UN's Low Band DXing radial
lengthcalculations.
Dear OMs and Yls,
I am replacing raised radials for 160M inverted L with ground
mounted
radials mostly because I could not readily get the raised radials up
high
enough in my wood and also because of maintenance problems.
This inverted L goes up 100 feet at its top before levelling out
for
the final 32' or so. It should I believe have a strong vertical
element.
ON4UN's book Low-Band DXing 56th edition is generally excellent
but I
do find the coverage of ground radials both confusing and somewhat
contradictory. This surprises me for what is pretty much considered
the
bible.
On page 9-14 the text states that the velocity factor falls for
ground mounted radials to the "the order of 50-60%, which means that a
radial that is physically 20 meters long is actually a half-wave long
electrically!" This example is for 80M not 160M. However in the
examples
found on page 9-15 the velocity factor change is ignored. I
understand
the velocity factor change and have always accepted this. It generally
did
not pay to try and cut radials precisely to a given wavelength. I
accept
the radial length vs. radial number charts but is this an electrical
length
in free space or a length considerably reduced due to velocity factory
change? Example 3 ignores velocity factor correction and from what I
can
see this correction is ignore in most of the text concerning ground
radials.
What does one do? Who does one believe.
While I am talking about a 160M inverted L; I did reference the
SteppIR BigIR vertical manual, page 18. Lengths should be scalable. I
find no mention of velocity factor and the shortening effect which is
experienced. The recommendations are not very different from those in
ON4UNs book. So does this mean one ignores the change in velocity
factor?
I appreciate some guidance with this matter. I would like a
radial field which would take me to within 0.5/1 dB of the maximum
achievable for reducing near field losses.
73 Doug EI2CN
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