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FM GROUNDWAVE
- Thread starter fangio28
- Start date
Educate me here. Is there any such thing as FM GROUNDWAVE?
fangio28 said:
My farthest is about 100 miles on some Houston stations. Keep in mind these are their 100K stations that transmit from the 2,000-foot TV towers in Missouri City, and this was on mostly flat terrain between Houston and San Antonio. Going straight north out of Houston, you go through hills between there and Huntsville which considerably limits the reach.
Here in the Midwest, at least east of the Mississippi, 80 miles is considered exceptional.
fangio28 said:
No.
"Skywave" and "groundwave" are things that happen with LW, MW and SW broadcasts. FM signals are line of sight, so if you are lucky enough to get e-skip - it's merely an extension of the line of sight signal as it travels beyond the horizon and is bounced off the atmosphere.
Under certain conditions AM signals have the ability to travel along the ground well beyond the horizon. This is the component of the AM signal that is associated with the AM transmitter's ground system. The groundwave depends upon the relative conductivity of the soil in a given place in order to be effective. For example, salt water is a fantastic conductor of groundwave which is why many New York AMs are receivable day and night on Cape Hatteras, NC despite being hundreds of miles over the horizon - that is the groundwave signal doing its thing. If you live at a certain distance from a 50 kw signal (generally 80-200 miles), you'll hear the signal get worse at night with echoes and fading. That phenomena is the groundwave and skywave meeting each other at your location. The skywave takes a fraction of a second longer than groundwave does so they are out of sync.
This doesn't happen with FM. Many of the engineers here can explain all this better than I can but I wanted to make it clear that no, there's no such thing as "FM groundwave".
ALLOW ME TO REPHRASE THE QUESTION...what is the maximum line-of-sight
one can expect to hear? In other words, non-trop or E-skip, etc.
In limited tries, with only the car radio, i have heard several over 100 miles,
including one Canadian. I'm 100 miles south of BC in N Idaho.
On AM, ground conductivity (contrary to maps) seems pretty good based on
my experience DXing from 8 different states previously.
one can expect to hear? In other words, non-trop or E-skip, etc.
In limited tries, with only the car radio, i have heard several over 100 miles,
including one Canadian. I'm 100 miles south of BC in N Idaho.
On AM, ground conductivity (contrary to maps) seems pretty good based on
my experience DXing from 8 different states previously.
The DXers in the Worldwide TV-FM DX Association use the term "groundwave" to refer to reception that's not enhanced by tropo ducting, E-skip, meteor scatter, etc. No, it's not technically correct, but it's become the commonly-accepted term.
How far can you get a signal line-of-sight? It depends on the height of the transmitting antenna and the height of your receiving antenna. The horizon is considerably more distant from up on a 2000-foot tower than it is at ground level.
How far can you get a signal line-of-sight? It depends on the height of the transmitting antenna and the height of your receiving antenna. The horizon is considerably more distant from up on a 2000-foot tower than it is at ground level.
That's actually a tough question, without getting into the esoterica of groundwave vs. line of sight ("LOS").
What one can hear via LOS is basic math. The formulae are available on the Internet and other places. Remember, radio line of sight is slightly further than visual LOS.
But, this doesn't account for troposcatter, a minor enhancement vehicle that is very routinely operative. It's troposcatter that is often responsible for the big class Cs showing up where they really should not be audible. I guess here in Memphis, the best example might be what I hear on 100.3 from Little Rock. I can hear it on my car radio almost anytime at ~150 miles. With an nice antenna at home, I am sure one could expect even better.
DE
What one can hear via LOS is basic math. The formulae are available on the Internet and other places. Remember, radio line of sight is slightly further than visual LOS.
But, this doesn't account for troposcatter, a minor enhancement vehicle that is very routinely operative. It's troposcatter that is often responsible for the big class Cs showing up where they really should not be audible. I guess here in Memphis, the best example might be what I hear on 100.3 from Little Rock. I can hear it on my car radio almost anytime at ~150 miles. With an nice antenna at home, I am sure one could expect even better.
DE
OK, now I'll rephrase: you wouldn't refer to an FM signal as "groundwave" as you do with an AM signal, would you? Even though FM signals can get reflected by certain layers of the atmosphere, they still travel in what is generally a straight line (reflection from mountainous terrain being a slight exception).
So, is there actually such a thing as FM "groundwave" or FM "skywave"? Because I was always under the impression that FM and higher frequencies have a straight-line signal based on line of sight or reflected line of sight. MW signals can curve with the earth - doesn't that make it different?
So, is there actually such a thing as FM "groundwave" or FM "skywave"? Because I was always under the impression that FM and higher frequencies have a straight-line signal based on line of sight or reflected line of sight. MW signals can curve with the earth - doesn't that make it different?
The FCC used the term groundwave to refer to the normal propagation of FM frequencies on their early F(50,50) and F(50,10) graphs. I guess that was because people were used the the normal daytime propagation of AM signals being called groundwave. Actually, if you look at the details of Longley Rice prediction variables, ground conductivity is one of the variables. The radio line of sight exceeds the geometrical or optical line of sight.
Before the Docket 80-90 allotments, it was not unusual to get a few scattered stations as far as 250 miles under fairly normal conditions. From my locations in SE Michigan, this included Erie, Akron, Ft. Wayne, Chicago, Milwaukee, Green Bay, and Petoskey with a selective receiver and good gain and directivity FM beam antenna.
Before the Docket 80-90 allotments, it was not unusual to get a few scattered stations as far as 250 miles under fairly normal conditions. From my locations in SE Michigan, this included Erie, Akron, Ft. Wayne, Chicago, Milwaukee, Green Bay, and Petoskey with a selective receiver and good gain and directivity FM beam antenna.
"He means "what is the furthest deep fringe fm reception" on a normal day without tropo or e-skip"
In the (real) old days we would have this in the mornings on
50 Mhz 6 meter AM.You could work out to ~50-75 miles.It
was called "extended groundwave" then.
For whatever reason there seems to be an enhancement around
local sunset on VHF in general,including the VHF AM air band.
It doesn't last long.FM b/c also benefits,sometimes around
sunrise,too.Probably nothing to do with greyline reception
but definitely another interesting propagation thing.
http://dx.qsl.net/propagation/greyline.html
In the (real) old days we would have this in the mornings on
50 Mhz 6 meter AM.You could work out to ~50-75 miles.It
was called "extended groundwave" then.
For whatever reason there seems to be an enhancement around
local sunset on VHF in general,including the VHF AM air band.
It doesn't last long.FM b/c also benefits,sometimes around
sunrise,too.Probably nothing to do with greyline reception
but definitely another interesting propagation thing.
http://dx.qsl.net/propagation/greyline.html
Well, for me, I can get FM groundwave from good distances. I live just S of Charleston, and I can get the big Hilton Head and Savannah stations almost 100% of the time. These stations are about 70-90 miles away. Columbia comes in also, along with WTCB from Orangeburg.
There's "groundwave" and there's "groundwave." Here in western NY, I can usually get decent reception from 107.3 in Utica (which just changed calls to WKVU), some 120 miles to the east (even with another less-powerful semi-local, WHTK-FM, much closer).
But that's far from my most distant regular reception. When I was living in the high desert of California (eastern Inyo County, 30 miles east of Bishop near the Nevada border), I could regularly pull in several FMs from Cuesta Peak in San Luis Obispo, more than 200 miles to the west on the California coast. The path was apparently enhanced by knife-edge diffraction through the High Sierras and the White Mountains. "Groundwave?" You tell me...
But that's far from my most distant regular reception. When I was living in the high desert of California (eastern Inyo County, 30 miles east of Bishop near the Nevada border), I could regularly pull in several FMs from Cuesta Peak in San Luis Obispo, more than 200 miles to the west on the California coast. The path was apparently enhanced by knife-edge diffraction through the High Sierras and the White Mountains. "Groundwave?" You tell me...
Wow! What a thread has developed in one day!
I got my FCC First Phone in 1960 or 61 as I recall. I am not a professional engineer by training, but I followed the broadcasting world very closely for several years, and at a little bit of distance since then. I maintain that among broadcasters and among the FCC types and the industry that supports the world of broadcasting, the answer is: "There is no GROUNDWAVE in F.M. Broadcasting!"
However, among the enthusiasts of DX listening and logging, it has obviously become an accepted terminology to describe what others might refer to as "sirect reception of free-space propogation" or some other academic sounding terminology.
This has been the year of the "Truth-O-Meter" in political journalism. I guess we can say that on this topic, everybody said something that is "partially true".
Happy tuning, DXers.
I got my FCC First Phone in 1960 or 61 as I recall. I am not a professional engineer by training, but I followed the broadcasting world very closely for several years, and at a little bit of distance since then. I maintain that among broadcasters and among the FCC types and the industry that supports the world of broadcasting, the answer is: "There is no GROUNDWAVE in F.M. Broadcasting!"
However, among the enthusiasts of DX listening and logging, it has obviously become an accepted terminology to describe what others might refer to as "sirect reception of free-space propogation" or some other academic sounding terminology.
This has been the year of the "Truth-O-Meter" in political journalism. I guess we can say that on this topic, everybody said something that is "partially true".
Happy tuning, DXers.
Back in the early 1980s, I had the Archer/Antennacraft FM-10 mounted on a tripod and Alliance T-45 Tenna Rotor. The overall height was about 30 feet above ground. I was about 42 miles NW of WRIF 101.1 in Detroit. There happened to be a null at just the right place where I could null out WRIF and get WBRN Big Rapids 3000 watts on 100.9 about 100 miles away and WIXX Green Bay (A Class C around 100 kW) on 101.1 about 220 miles away on a fairly regular basis.
One thing we haven't attributed the DX to in this discussion is scattering.
One thing we haven't attributed the DX to in this discussion is scattering.
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