1Edge vs. 2Edge

Mixer

DTVUSA Rookie
#1
I've run a few TVFool charts tracking what channels I'm supposed to get. I've gone through the FAQs but I've never really found an answer about the difference between channels listed with 1Edge or 2Edge. I'm guessing it's the amount of signal that's able to reach my house, but I'd like to know what a better definition is and how either 1Edge or 2Edge is measured. Thanks in advance.
 

Don_M

DTVUSA Member
#2
:welcome: , Mixer!

The notations refer to the number of mountains, ridges, hills -- even the curvature of the earth itself, if the signal is more than 70 miles out -- that obstruct the direct path (a.k.a. "line of sight," or LOS) between your receive antenna and the broadcaster's transmit antenna. Two edges block more signal than one edge does. The height of the ridge top(s) relative to your location also impact signal strength.
 

Mixer

DTVUSA Rookie
#3
Thank you Don. I noticed that by adjusting the height up on my tvfool input, a few of my channels went from 2Edge to 1Edge. Unfortunately, TVFool predicts a good 50' gain in height for my farmhouse located about 2 hours south of Chicago to receive a few of the city located broadcast towers.
 
#5
A "1-edge" signal is diffracted once.

A "2-edge" signal is diffracted twice - that is, a 1-edge diffracted signal is diffracted yet again by a second terrain obstacle. This further weakens the signal beyond the simple loss caused by a change in distance.
 

bicker

DTVUSA Member
#6
Okay, that's was my understanding... that 2Edge is specifically at diffracted at least twice. I thought that the distinction was made, because, theoretically, with 1Edge, you have a chance of getting a single instance of the signal, while with 2Edge you're almost surely going to experience multi-path -- is that not the distinction?
 

Don_M

DTVUSA Member
#7
... theoretically, with 1Edge, you have a chance of getting a single instance of the signal, while with 2Edge you're almost surely going to experience multi-path -- is that not the distinction?
Signal diffraction isn't quite the same phenomenon as signal reflection. Signals diffract, or bend, around obstructions that can be many miles away, but the obstructions don't cause signal reflections by themselves. (That's not to say diffracted signals can't ever be reflected by other objects, however.)

Multipath happens when a signal bounces off a third object and arrives at the receive antenna, usually (but not always!) later. These reflective objects are almost always within a mile or two. Sometimes they're mere yards away, such as in an attic or near a chimney. The farther away the reflective surface, the longer the reflected signal gets delayed. These delays are measured in nanoseconds.

This is a really basic description. You might be interested in Ken Nist's terrific discussion of diffraction here. It's far more enlightening than any explanation I could offer.
 
#8
Okay, that's was my understanding... that 2Edge is specifically at diffracted at least twice. I thought that the distinction was made, because, theoretically, with 1Edge, you have a chance of getting a single instance of the signal, while with 2Edge you're almost surely going to experience multi-path -- is that not the distinction?
I think that you understand some of the difference between 1 edge and 2 edge. Much of it is signal strength. VHF does much better for signal strength in a 2 edge situation than UHF.

However, the term multipath is misleading. Most folks understand it to mean two distinct paths from the transmitter to the receive antenna, such as a reflection off of a nearby object. In a 2 edge environment, the edge of the first hill causes the signal to loose focus. Some of the unfocused energy gets diffracted back to the receive antenna, but via a second, slightly different knife edge. Yes, it's multipath, but the difference in path lengths is smaller. The diffraction in a 2 edge situation can cause the equalizer in the HDTV decoder to work harder.
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#9
:welcome: Mixer! Thanks for your interesting question and thanks to Don_M and Tower Guy for their explanations. The link posted wasn't new to me and it is terrific, now that I can connect the Edge terms to it. I get it.

Ironically, I contacted Jay about a week ago asking him if someone could post a DTV USA Forum Glossary definition http://www.dtvusaforum.com/forum-help-zone/2694-attention-members-we-need-your-input.html of 1Edge VS 2Edge ... starting with the word Edge!

I read elsewhere, it had to do with the dBd level (blue VS red ring) shown on the REC Networks website maps, but that didn't make sense to me.

In my peculiar location, I have two 1Edge transmitters 0.8 miles from me and three 2Edge transmitters 2.9 miles away. It has been a (calm down Jim, no swearing here) REAL CHALLENGE to capture those stations and what it required is in my photo gallery here.

After reviewing my TVFOOL printout on all three Network transmitters (it calls two other locals 0.7 miles from me LOS) but in reality they are also 1Edge, so most of the stations I receive are 'edgy' ... :becky:

Jim

PS You guys are terrific!
 
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#10
I got a few that show up as 'tropo' but they come in whether tropospheric ducting is happening or not...what i am always amazed by is how i have to rotate my antenna every 15 minutes pickup up long distance stations and putting the antenna in an entirely different spot, not simply nudging it to make up for a slight loss, but actually a 180-240-degree shift. i never knew signals could 'move around' as if the station was a Starship in orbit constantly changing position like GPS satellites but that is what it appears to be sometimes. usually when that phenonemon happens there is zero wind and zero precipitation that would easily explain the sudden moving around i experience.
 
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BCF68

DTVUSA Member
#11
I got a few that show up as 'tropo' but they come in whether tropospheric ducting is happening or not...what i am always amazed by is how i have to rotate my antenna every 15 minutes pickup up long distance stations and putting the antenna in an entirely different spot, not simply nudging it to make up for a slight loss, but actually a 180-240-degree shift. i never knew signals could 'move around' as if the station was a Starship in orbit constantly changing position like GPS satellites but that is what it appears to be sometimes. usually when that phenonemon happens there is zero wind and zero precipitation that would easily explain the sudden moving around i experience.
That's because they are "tropo" meaning the signal is bouncing off the troposphere which as you know not exactly some prefect calm flat surface.
 

FOX TV

Contributor
#12
Tropo Ducting

I got a few that show up as 'tropo' but they come in whether tropospheric ducting is happening or not...what i am always amazed by is how i have to rotate my antenna every 15 minutes pickup up long distance stations and putting the antenna in an entirely different spot, not simply nudging it to make up for a slight loss, but actually a 180-240-degree shift. i never knew signals could 'move around' as if the station was a Starship in orbit constantly changing position like GPS satellites but that is what it appears to be sometimes. usually when that phenonemon happens there is zero wind and zero precipitation that would easily explain the sudden moving around i experience.
Tropospheric ducting is not the same phenomenon as a reflected signal off of a layer of the atmosphere that can be observed in the AM Broadcast band at night, as these low frequency signals do actually reflect off of the atmospheric layers at night.

Tropo ducting occurs mainly when there are two layers of the atmosphere that are distinctly different in temperature that exist above and below each other. This temperature difference of the layers forms a kind of "Duct" that allows signals to travel in between these temperature layers, thus the term tropospheric ducting.

The entry and exit points of the duct can exist for hours or minutes, and this may explain why readjusting of the antenna may be needed to keep a good lock on a tropo signal as the conditions that cause this phenomenon can change at a moments notice.

Tropospheric ducting mainly effects the Low VHF band, and possibly the high VHF channels at times also. It is rarely observed at frequencies in the UHF range, as they have to ability to "Punch Through" the ducting layers due to their short wavelengths.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#13
Tropo event?

FOX TV,

Based on your explanation I think I experienced an 'episode' of Tropospheric Ducting about a month ago. I was watching a low power translator due west of me on my CM-4228 which is mounted well under my roofline in my back yard. When I changed channels, I noticed channel 12 was pixelating and blocking - and its' never done that before!

That's when I remembered I was using the wrong antenna, so I switched to my dedicated '12' Yagi which is pointed north and the signal level was pegged, instead of its normal 65: this is the only antenna that captures '12' for me, and they are 75 miles away. I switched to my '48' Yagi (just over my roofline pointed east) and '12' was coming in at 15-20 and quite stable.

I checked one hour later and the signal from '12' was unuseable on any antenna, like someone had closed a valve. The following morning everything had returned to 'normal'.

You also wrote: "It is rarely observed at frequencies in the UHF range, as they have to ability to "Punch Through" the ducting layers due to their short wavelengths."

-- so, since my '12' is actually channel 35, did this event fit the definition of Tropo? Thanks,
Jim

A photo of my 4228 pointed west (not north) is attached below. It should explain why capturing any channels from the east is a bit of a challenge here!
 

Attachments

FOX TV

Contributor
#14
FOX TV,

Based on your explanation I think I experienced an 'episode' of Tropospheric Ducting about a month ago. I was watching a low power translator due west of me on my CM-4228 which is mounted well under my roofline in my back yard. When I changed channels, I noticed channel 12 was pixelating and blocking - and its' never done that before!

That's when I remembered I was using the wrong antenna, so I switched to my dedicated '12' Yagi which is pointed north and the signal level was pegged, instead of its normal 65: this is the only antenna that captures '12' for me, and they are 75 miles away. I switched to my '48' Yagi (just over my roofline pointed east) and '12' was coming in at 15-20 and quite stable.

I checked one hour later and the signal from '12' was unuseable on any antenna, like someone had closed a valve. The following morning everything had returned to 'normal'.

You also wrote: "It is rarely observed at frequencies in the UHF range, as they have to ability to "Punch Through" the ducting layers due to their short wavelengths."

-- so, since my '12' is actually channel 35, did this event fit the definition of Tropo? Thanks,
Jim

A photo of my 4228 pointed west (not north) is attached below. It should explain why capturing any channels from the east is a bit of a challenge here!
Hello again Jim,

Tropo at UHF frequencies is not impossible, but it is much more rare than at frequencies around 50 to 80 MHz., which some consider the cut off point for long distance or "Skip" signals. We do see openings above 50 Mhz fairly often, but the conditions for UHF ducting are very rare, and seem to be more prevalent during summer months when there seems to be a greater potential for ducting conditions to form due to thunderstorm activity
 
#15
TVfool's use of the term "Tropo" refers to tropospheric scattering rather than ducting.

They are different physical phenomenons. Think of "scattering" the same way that the sky gradually darkens at dusk on a clear evening. As the source of light disappears further beyond the horizon, the amount of light reflected from the atmosphere diminishes until it is gone. This light is diffuse and is not strongly defined as it weakens.

Ducting would be more akin to over-the-horizon sunlight reflecting off a specific cloud formation and providing unexpected illumination until either the cloud formation moves or the sunlight goes much further over the horizon. There may be short intervals where the light is much stronger but they are quite transitory.
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#16
FOX TV and ProjectSHO89,

If the astonishing gain and then loss of signal strength I witnessed was not a Tropo event, what else could have caused it?
Jim
 
#17
FOX TV and ProjectSHO89,

If the astonishing gain and then loss of signal strength I witnessed was not a Tropo event, what else could have caused it?
Jim

Again, there are two types of "tropo": Ducting and Scatter. TVfool's table only deals with "scatter" predictions and nothing related to "ducting".

You were experiencing a transitory "duct" that allowed a very strong signal to propagate to your location that was relatively short in time duration.

Think of it as a wandering wormhole if you're a "Deep Space Nine" fan....
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#18
ProjectSHO89 wrote:

Again, there are two types of "tropo": Ducting and Scatter. TVfool's table only deals with "scatter" predictions and nothing related to "ducting".

You were experiencing a transitory "duct" that allowed a very strong signal to propagate to your location that was relatively short in time duration.

Think of it as a wandering wormhole if you're a "Deep Space Nine" fan...
--------

ProjectSHO89,

I know DS9 and that's a great analogy and it fits what I experienced that bizarre evening. Like a tube (duct) that was wide open or closed. Apparently not commonly seen or recognised when they happen.

I experienced (enjoyed) scatter and 'back-scatter' from my low band CB and Ham days. Seattle to Tokyo was a direct line, but Seattle to Portland, Oregon was a rarity. I find it hard to believe the TVFOOL table can anticipate anything like that, especially regarding UHF.

But, I'm now thinking after I finalize my home antenna system I should build some special antennas to try for HDDX. <---Did I just invent a new one??? LOL+
Jim
 
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BCF68

DTVUSA Member
#19
Tropospheric ducting mainly effects the Low VHF band, and possibly the high VHF channels at times also. It is rarely observed at frequencies in the UHF range, as they have to ability to "Punch Through" the ducting layers due to their short wavelengths.
Explain why then when there is tropospheric ducting in my area that I get in all kinds of UHF stations from as far as 300 miles away then?
 

BCF68

DTVUSA Member
#20
Again, there are two types of "tropo": Ducting and Scatter. TVfool's table only deals with "scatter" predictions and nothing related to "ducting".
Actually more than 2. Scatter is what TVfool is referring too. Enhancement is why you get some stations in at night but not day. An Ducting is when you get those far off stations you shouldn't normally get in. At any rate any "tropo" station should never be counted on to be reliable no matter how strong TVfool may list their signal strength.

A)Tropospheric Scatter (TrS)

...is ever-present under normal conditions. That's the mode that produces the distant fluttery signals that randomly fade in and out. These are your most distant regular stations that barely make it in. Depending on your location and equipment..tropo scatter can extend to 300..500..or even 700 km. The theoretical maximum limit for most TV/radio DXers is 800 km (500 mi) (Some semi-professional setups can extend furthur). Scatter is caused by small particles/droplets in the air such as haze, dust, volcanic ash, clouds, etc.

B)Tropospheric Enhancement (TrE)

...(a.k.a. Tropospheric Refraction)... is common under normal conditions. On most clear nights with calm or light winds..the ground radiates and the air near the ground cools. Eventually an inversion is formed and signals begin to refract off the inversion. Stations that normally fade in and out via tropo scatter come in continuously..with increasing strength. Also..weaker tropo scatter stations that are normally not heard (because their signal strengths never cross the background noise threshold signal level) also begin to appear. When the sun comes up..the ground & air heats up..the inversion breaks down..and the enhancement disappears. The enhancement is subtle on some nights..and very obvious on other nights. Distances are no different than with tropo scatter..it's just that the signals are stronger and interference is more intense. Tropo enhancement is greatly influenced by terrain..with valley and coastal paths favoured. ("Fog-prone" areas are also "tropo-prone" areas.). From any one receiving location, multiple directions usually are enhanced at the same time.

C) Tropospheric Ducting (TrD)

...is an abnormal condition. An inversion has formed at a much higher level above the ground...the vast majority of duct-producing inversions lie between 450 and 1500 m (1500 to 5000 ft)..with a few between 1500 and 3000 m (5000 to 10,000 ft). These inversions are not formed due to nighttime radiation/cooling..but rather because of some other weather phenomenon (high pressure subsidence aloft, warm frontal boundary, cold frontal boundary, oceanic or lake inversion, Chinooks, etc.). Because of this..ducting can occur day or night (though it strengthens at night)..is not usually influenced by terrain (the exception being large mountain chains like the Rockies)..and from a DXers point of view is usually either uni- or bi-directional. In fact..typical ducts are sharply directional. Signals refract off of and also travel along the inversion..thus the analogy of a duct. Strong ducting can result in super-refraction where signals are bent so far in a downwards direction that they actually hit the ground and reflect off it, only to bounce of the top of the inversion again and so on. Distances are theoretically unlimited. One large area can have multiple ducts going on simultaneously..but they are usually parallel paths. It is possible in a very strong high pressure system to have large areas of ducting creating multi-directional openings. These are the rare "blockbuster" openings that bring signals great distances and cause havoc with interference. They are most common over the oceanic areas in the tropics and sub-tropics.

Tropospheric DX Modes
 
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