John S wrote:
On 1/20/2015 12:30 PM, wrote:
wrote:
snip
A vertical generally needs radials unless it's a "1/2 wave" type
design. And even good verticals can be quite lackluster for close
in work compared to a low dipole on 40m. Good at night to DX though.
But like I say, he's gotta decide what he wants to concentrate on,
and go from there.
You are all over the place here and mixing apples and oranges.
In what way? Seems perfectly reasonable and informative to me.
A vertical has a low elevation angle.
You will have to describe the conditions for that to be a truthful
general statement. Do you mean ground mounted with buried radials,
radials lying on the surface, elevated verticals with radials, or
half-wave verticals with no radials?
Most people mean ground mounted when they use the term vertical and
ground plane for an elevated vertical.
I meant ground mounted and the radials or lack of them is essentially
irrelevant.
Any antenna that has a low elevation angle is "better" for distant
communications than an antenna with a very high elevation angles.
I think that is agreeable by all.
I would certainly hope so.
A horizontal antenna less than a half wavelength in height has a vey
high elevation angle. At .3 lambda it is 48 degrees, at .25 lambda
it is 62 degrees, and at .2 lambda it is 90 degrees, i.e. straight up.
According to the simulation programs, that is probably true.
As well as basic physics.
But, that
is the angle of *maximum* radiation. How much signal is available at the
3dB, 6dB, 10dB, 20dB angles? If you are running 100 watts, you still
have 1 watt available at the 20dB angle.
I would be glad to run the numbers for you.
Do you want it as a comparsion between a vertical with no radials,
a vertical with radials, both over average ground, and a vertical
with perfect ground?
This is called an NVIS antenna which is "better" for local communications
out to about 500 miles or so on the lower bands. NVIS communcations is
nearly nil much above 8 MHz at other than sunspot peaks. We are currently
past the peak of the current sunspot cycle and heading for a minimum.
Can you supply support to some other source for this conclusion?
I assume you mean for NVIS communications and not the sunspot cycle:
http://en.wikipedia.org/wiki/Near_ve...idence_skywave
http://www.w0ipl.net/ECom/NVIS/nvis.htm
http://www.w5jck.com/nvis/W5JCK-NVIS...esentation.pdf
https://www.txarmymars.org/.../NVIS-...and-Design.pdf
http://www.qsl.net/wb5ude/nvis/
http://home.centurytel.net/w9wis/NVIS.html
Want more?
A vertical antenna does not "need" radials, but it's performance is
improved by radials.
It depends on the design.
The design is a metal tube about .25 lambda long mounted close to the
ground and fed at the bottom end.
A vertical antenna over average ground has a main lobe at about 30 degees
and a gain of about 1 dBi.
Please supply configuration of the antenna as mentioned above.
A metal tube about .25 lambda long mounted close to the ground and fed at
the bottom end.
A vertical antenna over perfect ground has a main lobe at 0 degrees and
a gain of about 5 dBi.
Again, please supply configuration of the antenna as mentioned above.
A metal tube about .25 lambda long mounted close to the ground and fed at
the bottom end.
In a typical urban setting where there is landscaping and irrigation,
the ground is most likely average to very good unless you are in the
middle of a desert, which means even without radials the vertical's
gain is going to be a few dBi. Adding a few radials will improve the
gain and lower the main lobe but are not absolutely necessary.
I think this is unsubstantiated unless you can supply supporting
documentation.
Trivially demonstrated by any antenna simulation program.
Or are you looking for numbers on ground conductivity?
Google ground conductivity
Want to measure it yourself, read this:
http://www.technik.dhbw-ravensburg.d...ductivity.html
Most verticals will get put in the middle of a lawn and it is trivial
to take a lawn edger or weed wacker and cut a groove in the grass down
to the dirt and staple down some radials. In such a setting you do
NOT need the 120 radials of a commercial broadcast station with it's
antenna in a barren field.
Most verticals will be installed depending on the installers resources,
abilities, and present knowledge of antennas.
The same can be said for making cookies; so what?
One of the purposes of this group is the dissemination of antenna
knowledge. I make no assumptions about the readers other than the
ability to read.
If he has trees to tie dipole legs to, he really only needs one
support for the apex.
The bottom line is a horizontal antenna needs three supports.
Actually, a 40 meter dipole can use two supports (trees) and can work
the US easily with a 50W transmitter.
Sure, if you use very heavy wire for the dipole and very light feed line.
BTW, most amateur rigs these days put out 100 Watts.
--
Jim Pennino