Mountains don't simply block HF
dave
antenna, like turning on a lamp. When the field encounters an
obstruction it "knife-edges" and Fresnel zones are created, which may
help or totally prevent reception, depending on the math (distance from
transmitter to obstruction, from obstruction to receiver, blah blah). I
am in a box canyon, open only to the South. If mountains stopped the
signals completely, all I'd get would be penguins.
bpnjensen
A sort of diffraction effect. Makes sense. - however, I would bet
some RF is blocked by either reflection or absorption, and the
probable chaotic diffraction from irregular edges likely results in a
pretty unpredictable pattern.
arthr...@webtv.net
We 'll have a couple of penguins as future candidates in the 2012
elections . POTUS and VP . They make more sense . Horses as well .
They are even smarter .
arthr...@webtv.net
I don't quite picture this : mountains and canyons . Obviously-- no
line of sight signals such as local AM and FM broadcasts, very poor
groundwave propagation . Now, why is skywave affected as well ? What
can possibly block HF signals ?
dave
That's what Fresnel zones are.
dave
The good skywaves come from 10 to 20 degrees up. The mountains are
higher than that. I get no VHF/UHF TV. I get FM from Mt. Wilson,
severely degraded. I get MW like gangbusters.
arthr...@webtv.net
>
> - Show quoted text -
This must be a pretty good (quiet ) RF environment . When conditions
are great, though .
RHF
> On 02/13/2011 12:50 PM, arthrny...@webtv.net wrote:
>
>
>
> > On Feb 13, 3:26 pm, bpnjensen<bpnjen...@yahoo.com> wrote:
> >> On Feb 13, 12:09 pm, dave<d...@dave.dave> wrote:
>
> >>> The signals don't travel; a field is set up around the transmitter
> >>> antenna, like turning on a lamp. When the field encounters an
> >>> obstruction it "knife-edges" and Fresnel zones are created, which may
> >>> help or totally prevent reception, depending on the math (distance from
> >>> transmitter to obstruction, from obstruction to receiver, blah blah). I
> >>> am in a box canyon, open only to the South. If mountains stopped the
> >>> signals completely, all I'd get would be penguins.
- - - A sort of diffraction effect.
- - - Makes sense. - however, I would bet some RF
- - - is blocked by either reflection or absorption,
.
The natural Earthen Ground is a great Equal Opportunity
Energy Absorber of all kinds of Energy : Sunlight, Metors;
RF/EMF; Plant Life; even our Foot Falls . . .
.
All the Incoming Radiated Energy [EMF]
has to go somewhere :
* Either Bounces Off {Less than 100%}
-or-
* Attempts to Pass/Go Through {Less than 100%}
* * Actually Passes Through {Very Little}
-or-
* * Gets Absorbed {A Lot}
* * * Some of Both often with most getting
Absorbed and little Passing Through.
-cause- The natural Earthen Ground is a great
Energy Absorber of all kinds of Energy.
.
- - - probable chaotic diffraction from irregular edges
- - - likely results in a pretty unpredictable pattern.
- - I don't quite picture this : mountains and canyons .
- - Obviously-- no line of sight signals such as local
- - AM and FM broadcasts, very poor groundwave propagation .
- - Now, why is skywave affected as well ?
- - What can possibly block HF signals ?
- The good skywaves come from 10 to 20 degrees up.
- The mountains are higher than that. I get no VHF/UHF TV.
- I get FM from Mt. Wilson, severely degraded.
- I get MW like gangbusters.
Dave,
Near Vertical Incident Skywave (NVIS) Antenna :
-by- W0IPL
http://www.w0ipl.net/ECom/NVIS/nvis.htm
"Sky-Wave" -to- 'Sky-Wire' Antenna
* NVIS Antennas and HF Propagation
-by- KV5R
http://www.athensarc.org/nvis.asp
* "NVIS" High Frequency [HF] Antennas
-by- W9WIS
http://home.centurytel.net/w9wis/NVIS.html
* NVIS Antenna Presentation
-by- W5JCK
http://www.w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.pdf
.
=ABOUT= Near Vertical Incidence Skywave [NVIS]
http://en.wikipedia.org/wiki/Near_Vertical_Incidence_Skywave
-about- Skywave
http://en.wikipedia.org/wiki/Skywave
.
A Large Full-Wave "Sky-Wire" Loop Antenna
-for- the 160m Amateur [HAM] Radio Band
would be ~281.2 Feet Around ~85.7m and
Set @ < 1/8WL above ground ~35 Feet ~10.7m
.
-or- For Shortwave Radio Listeners [SWLs]
One or more Smaller 1/2 WL Loop Antennas
and Set @ < 1/10th WL above ground
.
120m Shortwave Band : 2300 to 2498 kHz
Roughly ~213.9 Feet with a General
Average Diameter 68.1 Feet and
Set @ < 42.8 Feet above ground
.
90m Shortwave Band : 3200 to 3400 kHz
Roughly ~153.8 Feet with a General
Average Diameter 49 Feet and
Set @ < 30.8 Feet above ground
.
60m Shortwave Band : 4750 to 4995 kHz
Roughly ~103.6 Feet with a General
Average Diameter 33 Feet and
Set @ < 21 Feet above ground
.
49m Shortwave Band : 5950 to 6250 kHz
Roughly ~82.7 Feet with a General
Average Diameter 26.3 Feet and
Set @ < 16.5 Feet above ground
.
41m Shortwave Band : 7100 to 7300 kHz
Roughly ~69.3 Feet with a General
Average Diameter 22 Feet and
Set @ < 13.9 Feet above ground
.
31m Shortwave Band : 9500 to 9900 kHz
Roughly ~51.8 Feet with a General
Average Diameter 16.5 Feet and
Set @ < 10.4 Feet above ground
.
25m Shortwave Band : 11,650 to 11,975 kHz
Roughly ~42.3 Feet with a General
Average Diameter 13.5 Feet and
Set @ < 8.5 Feet above ground
.
=Caution=Warning= Below this 8.5 Feet Rigging Height
the Wire Antenna Element starts to become a Safety
Hazard for Tripping Falling and Head/Throat Injuries
.
21/22m Shortwave Band : 13,600 to 13,800 kHz
Roughly ~36.2 Feet with a General
Average Diameter 11.5 Feet and
Set @ < 7.25 Feet above ground
.
19m Shortwave Band : 15,100 to 15,600 kHz
Roughly ~32.6 Feet with a General
Average Diameter 10.4 Feet and
Set @ < 6.5 Feet above ground
.
.
iane ~ RHF
.
.
dave
> .
> .
> iNane ~ RHF
> .
> .
>
RHF
- 'Special-Dave's [edit] : "iNane" ~ RHF
- - On 02/13/2011 07:18 PM, RHF wrote:
-was-and-still-is-
Near Vertical Incident Skywave (NVIS) Antennas
-cause-
Mountains Can't Block All Shortwave Radio Signals [HF RF]
http://groups.google.com/group/rec.radio.shortwave/msg/fa59c30f736eb418
.
.
'Special-Dave',
It's Replies Like This That Make You 'Special' ;;-}}
inane'ly yours... iane ~ RHF
.
.
dave
NVIS is for local, not DX. The subject was reception of low angle
signals. NVIS is "near vertical". Near vertical is not low angle.
Learn to fucking read.
RHF
> On 02/14/2011 07:51 PM, RHF wrote:
>
>
>
> > On Feb 14, 6:49 am, dave<d...@dave.dave> wrote:
>
> > - 'Special-Dave's [edit] : "iNane" ~ RHF
>
> > - - On 02/13/2011 07:18 PM, RHF wrote:
>
> > -was-and-still-is-
> > Near Vertical Incident Skywave (NVIS) Antennas
> > -cause-
> > Mountains Can't Block All Shortwave Radio Signals [HF RF]
> >http://groups.google.com/group/rec.radio.shortwave/msg/fa59c30f736eb418
> > .
> > .
> > 'Special-Dave',
>
> > It's Replies Like This That Make You 'Special' ;;-}}
>
> > inane'ly yours... iane ~ RHF
> > .
> > .
- NVIS is for local, not DX.
Given a SWL'ers Location and Circumstances...
What You Get -is- What You Get :
Local : DX : or Both : and sometimes None
.
- The subject was reception of low angle signals.
NO Dave -to-quote-your-original-post-
"I am in a box canyon, open only to the South.
If mountains stopped the signals completely,"
-hence-my-reply-
Down in a Valley with High Mountains All Around
You : All Signals Are Near Vertical / High Angle
.
- NVIS is "near vertical".
Dave that is true.
.
- Near vertical is not low angle.
Dave that is true.
.
- Learn to fucking read.
Dave : ? "Learn to fucking read" ?
So anyone who doesn't reply back with what :
YOU WANT TO READ ~cant' fucking read~
=Conclusion= 'Special-Dave' : Proving Once Again
That You Are NO Libertarian of any stripe -but- an
Intolerant Elitist with Liberal-Fascist tendencies.
http://groups.google.com/group/rec.radio.shortwave/msg/920c3f7fdd38ee9b
-dave-too-much-medial-marijuana-smoking-again-
.
Dave your are talking about 'science' and "Science"
is good.
Where-As : I am talking about Shortwave Radio Reception
in the Mountains and Practical Ways of Achieving It.
For some {not-all} a NVIS Loop Antenna is a 'practical'
answer to being able to Hear something on the Radio;
when previously they could hear very little to nothing.
I reality most Shortwave Radio Listeners [SWL'ers] have
SWL Antennas that are more NVIS then Skywave :
Since their Antennas are too low at the lower SWL
Frequencies to be a Half-Wave Length of more Higher.
120m SW Band needs to be ~214 Feet for a 1/2WL
above the Ground; and ~107 Feet for a 1/4WL
90m SW Band needs to be ~154 Feet for a 1/2WL
above the Ground; and ~77 Feet for a 1/4WL
60m SW Band needs to be ~104 Feet for a 1/2WL
above the Ground; and ~57 Feet for a 1/4WL
49m SW Band needs to be ~83 Feet for a 1/2WL
above the Ground; and ~42 Feet for a 1/4WL
41m SW Band needs to be ~69 Feet for a 1/2WL
above the Ground; and ~35 Feet for a 1/4WL
.
= = = Many/Most SWL Antennas Are Lower = = =
-and-many/most-are-random-wires-less-than-50-feet-
.
31m SW Band needs to be ~52 Feet for a 1/2WL
above the Ground; and ~26 Feet for a 1/4WL
25m SW Band needs to be ~42 Feet for a 1/2WL
above the Ground; and ~21 Feet for a 1/4WL
21/22m SW Band needs to be ~36 Feet for a 1/2WL
above the Ground; and ~18 Feet for a 1/4WL
19m SW Band needs to be ~33 Feet for a 1/2WL
above the Ground; and ~16 Feet for a 1/4WL
.
.
Dave the 'Science' -says- many/most SWLs are
using SWL Antennas that are too-short and
too-low for the lower SW Frequencies and would
be considered to be designed for the Higher SW
Frequency Bands : 31m, 25m, 22m and 19m,
16m, 15m, 13m 11m.
BUT : We Work With What We Got [House & Lot]
AND : Do The Best We Can [Mostly Simple & Practical]
.
SWL 'Loop' Antenna : Going Beyond the Common
SWLer's Straight-Wire Antenna
For some/many SWL'ers Using a simple Random Wire
Antenna of 50~75 Feet Length be it a Horizontal Wire
Antenna; or an Inverted "L" Antenna at 15~30 Feet off
the ground; on the common Urban 'Lot' of 50'x100' with
a House etc on it.
For SWL'ers going to a Loop Antenna will give them
more Wire in-the-air in the available space that they
have an Urban 'Lot'.
* The Wire length will increase by 2X to 3X {That's 2X
to 3X the Wire In-the-Air and Better Signal Levels}
* But these SWL'ers can still only get the Wire
around 15~30 Feet Up-in-the-Air {off the ground}.
* The Large Loop Antenna's Signal Capture Area
is closer to 4X to 9X then the narrow straight Wire.
{That's 4X to 9X More 'possible' Signals}
-result- Better Signals and More Signals over the
straight Wire Antenna in the same Urban 'Lot'.
Most SWL'ers should be able to easily erect a
Loop Antenna for the 60m Shortwave Band :
{4750 to 4995 kHz} that is Roughly ~104 Feet
with a General Average Diameter 33 Feet and
Set @ < 21 Feet above ground on an Urban 'Lot'.
Some SWL'ers should be able to squeze-in a
Loop Antenna for the 90m Shortwave Band :
{3200 to 3400 kHz} that is Roughly ~154 Feet
with a General Average Diameter 49 Feet and
Set @ < 31 Feet above ground on an Urban 'Lot'.
.
Both would be 'practical' size SWL Antennas for
SWL'ers to consider for the average Urban 'Lot'
besides the conventional straight Wire Antenna.
.
Dave Dave Dave : "You" Can't Argue With 'Me'
-cause- You Are Stuck-On The Last Word of KISS :-{
-while- I Am Focused-On The Last Word of KISAP :o)
KISAP : Keep It Simple and Practical - iane ~ RHF
.
.