Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Mountains don't simply block HF
On Feb 13, 3:26*pm, bpnjensen wrote:
On Feb 13, 12:09*pm, 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, and the 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 ? |
#2
|
|||
|
|||
Mountains don't simply block HF
|
#3
|
|||
|
|||
Mountains don't simply block HF
On Feb 13, 3:59*pm, dave wrote:
On 02/13/2011 12:50 PM, wrote: On Feb 13, 3:26 pm, *wrote: On Feb 13, 12:09 pm, *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, and the 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.- Hide quoted text - - Show quoted text - This must be a pretty good (quiet ) RF environment . When conditions are great, though . |
#4
|
|||
|
|||
Near Vertical Incident Skywave (NVIS) Antennas -cause- MountainsCan't Block All Shortwave Radio Signals [HF RF]
On 02/13/2011 07:18 PM, RHF wrote:
. . iNane ~ RHF . . |
#5
|
|||
|
|||
Near Vertical Incident Skywave (NVIS) Antennas -cause- MountainsCan't Block All Shortwave Radio Signals [HF RF]
On Feb 14, 6:49*am, 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.r...59c30f736eb418 |
#6
|
|||
|
|||
SWL 'Loop' Antenna : Going Beyond the Common SWLer's Straight-Wire Antenna
On Feb 15, 5:42*am, dave wrote:
On 02/14/2011 07:51 PM, RHF wrote: On Feb 14, 6:49 am, *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.r...59c30f736eb418 * . * . '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 |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|