Question: two edge and one edge difraction what is it

scandiskwindows9x

Moderator of DTV Latino
#1
Hello Everyone:

i would like to know what does mean 1Edge: Single edge diffraction
2Edge: Double edge diffraction well i been looking up on google and yahoo and just get vague answers i wish know more in depth.

well by the way i am from Santiago Chile and we choosed the japanesse brazilean DTV system but is an fiasco the dtv that we choosed, get pixelated almost always, drops into black the image get noises in the sound and sometimes when the packages are losted the speed of the image get so slow like watch in slow motion instead of watch with the normal 29.97 fps the image and the colors ie the skin tones look yellowish and is of bad quality the colors.

i watched the ATSC or american DTV system in an demo in an store and was the reception very good just drops into black twice but the signal get recovered in 15 seconds and never gets pixelated and the place where was located the demonstration was an big avenue with lots of car traffic that was when the government and the tv channels was broadcasting in the 3 dtv system in test phase.

in resume was ATSC the best at my viewpoint

well hope that somebody can help me


greetings from Santiago Chile

scandiskwindows9x
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#2
Here is a discussion on the topic. Your English looks good enough to understand some of the more difficult terms.



Hope you are well in Chile, with the earthquake and all.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#3
Chile to adopt Japanese digital TV standard: Bachelet

September 14, 2009

Chilean President Michelle Bachelet as seen from a video camera speaking at a press conference in 2006. Chile will adopt the Japanese digital television standard ISDB-T, which is high-definition capable, joining neighboring Peru and Argentina, Bachelet said Monday.
Fascinating. I thought that all of the Americas were going ATSC - 8VSB.
 

scandiskwindows9x

Moderator of DTV Latino
#4
the difference is the follow

the original ISDB-T system works on MPEG2 and just can work with one HD Channel per frequency does not support virtual channels the japanesse brazilean system works on MPEG4 and by suing that video coding support virtual channels have an system called ginga that is based in java and use the data broadcast channel for send to the consumer questions, surveys and special contents of the programm that are watching, this interactivity system is already in developement.

both systems are based in COFDM modulation and have short radius coverage in fact in Santiago should install many antennas for have an good coverage and is like the gsm modulation of the cell phones GSM use OFDM and DVB-T ISDB-T uses COFDM , i have many papers abput the 3 system i will see if can upload them slowy according with my time avalaibility.

SBDTV = sistema brasileiro digital television that is the brazilean DTV system that is based in the japanesse system.
 

scandiskwindows9x

Moderator of DTV Latino
#5
well about me, my house does not have any structural damage and just our neighborns brick walls are in danger of colapse are just 3 of those brick walls in my street that are with danger of colapse, my brick wall is intact not have damage


just we are bad with the aftershakes just we get afraid.

but everything is ok.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#6
:welcome: Scan,

Here are links to a website where wave propagation is explained. The second page has excellent diagrams regarding 1-edge defraction. If a second 'obsticle' like a hill is also on the path between the transmitter and you, its 2-edge.

Most of the stations I receive here are 1-edge however, I also receive a 2-edge channel (580 kW ERP) from over 75 miles away.

Jim

Propagation Tutorial - Refraction and ducting <--home page

Propagation Tutorial - Diffraction <--page 2
 
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MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#7
Jim: Is there a more, ummm , simplified explanation?

Wow, thats a lotta info. I do Inderstand (Amatuer astronomer here) But do you know of a simplified diagram as it relates to radio / TV? I on occasion have to explain wave refraction / diffraction to some one and a "non tech" explanation is difficult for me. If I have to explain it to a non tech, I'd just kill myself first.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#9
Wow, thats a lotta info. I do Inderstand (Amatuer astronomer here) But do you know of a simplified diagram as it relates to radio / TV? I on occasion have to explain wave refraction / diffraction to some one and a "non tech" explanation is difficult for me. If I have to explain it to a non tech, I'd just kill myself first.
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Pogi,

I live on a hill less than a mile from three network transmitters, each with between 580 to almost 900 kW ERP ... but I'm 'over the side' of the hill and there is a 900 foot long 35 foot tall concrete retaining wall holding the side of the (same) hill just to my east, which puts me in an area shadowed from their signals. The diagrams on page two of the site I referenced above shows my 1-edge issue perfectly: literally, the retaining wall is a knife-edge barrier that cuts (or blocks) the usual expanding propagation of RF. Then, the following diagrams show the expanding wavefront and that explains how the shadowed 'zone' beyond the knife edge slowly fills back in, so the father away from the 'obsticle', be it a skyscraper, an apartment house or whatever, the more likely enough signal will be available to use.

Anyway, in the process of capturing those channels, I tried everything suggested by a number of local Engineers and then I did the opposite of what I was first told that would work for me: "a paperclip stuck into the back of my TV set". Eventually, I built a 12-bar 'cut-to-channel' Yagi which theoretically provides 12.5 dBd gain: bingo! That is my Project 38 Yagi.

Here is a link to a different website that also explains RF propagation VS obsticles. It shows different types of signal 'blockages' as well as differences between VHF and UHF signal attenuation. I hope this helps.

Jim

Siting the antenna
 

MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#10
Good diagrams!

As they say a picture is worth a thousand words. Sometimes hard to explain this to someone who just wants to know why their reception is different than their neighbors down the road here in the mountains of Utah.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#11
As they say a picture is worth a thousand words. Sometimes hard to explain this to someone who just wants to know why their reception is different than their neighbors down the road here in the mountains of Utah.
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Pogi,

I printed the pages from the second website and put them in a binder so they are available for me to show 'newbies' to the OTA world and help them better understand some of the potential complications in an antenna installation. You're spot-on: as you said, sometimes a picture is worth a thousand words - (especially if its the right picture)! :drinks:

Jim
 

scandiskwindows9x

Moderator of DTV Latino
#12
well where i live am very near of the Los andes mountain so will occur 1 and 2 edge diffractions also the transmitter is located at 6.83 miles far away or 11 kilometers the antennas of radio and television broadcasting are located in the San Cristobal mountain and its of 1.862 meters of altitude 6.10 ft of altitude .

the reception vary according with factors as the altitude of the mountain or surface where is the transmitter installed, complexity of the environment, bioldings, houses of large size or height because the signals "crash" virtually and get 1-2 edge diffraction the signal also have to consider the power that the signal is broadcasted from the main transmitter antena , is really many factors that have the air signals overcome to get throught your antenna.

ie in Chile is not widely used the roof antennas, is widely used the indoor antennas.
 
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