Ground Wave - How far does it propagate ?

[K1JJ]

I wanted to get some observations and opinions from others for "ground wave" distances on various bands.  What distance do you feel ground wave is significant vs: skywave on 75M, 160M and the broadcash band?

I'm trying to figure out at WHAT frequency area does the ground wave start to become significant. From my observations below, you will see I don't think it exists much on 75M, but do not know at what frequency it really begins to become a factor. Is vertical polarization mandatory to make it effective on the broadcash band?  Would a vertical extend it out significantly on 160M vs: a dipole?

Here's a few of my observations and thoughts:

75M:

Ground wave by itself is a constant, with little variation, right?  If this is true, then I feel it extends out no more than 5 miles on 75M. Here's what I've seen:

1) Once on 75M I made a CW contact with a friend who was about 3 miles away, around 12:30 in the afternoon on 3650.  His signal was swinging wildly from below S7 up to S9+60 over!  I never saw such variations, just like an oscillator. This was probably the ground wave and skywave adding and subtracting in such perfect amplitude and phase to cause this clean variation. Thus ground wave at 3 miles was about equal to skywave at that time.

2) How many times have I turned on the rig and could barely hear guys who were 10 miles away due to aurora or long skip on 75M?  I notice I can barely copy Big Al/ K1JCL two towns away at these times. If ground wave is constant, then it sure is weak only 10 miles away.


160M:

I am looking for opinions on this band, as I haven't spent a lot of time hanging there for local contacts to witness the band going really long and the effects of ground wave for locals ...


Broadcash Band: 

There seems to be a common belief that below 1.6 mhz there is substantial groundwave extending out many miles. How far and at what frequencies have you observed?  I think the time to tell is when the band is broke and long for local stations, just like 75M... 

73,
Tom, K1JJ

[W4MZ]

There used to be a midday net (noon) eastern on 1.845 here in FL where I have several times worked into coastal NC on slop bucket.  Both stations running abt 500 w and using inverted L's... I am located about a mile from the ocean near Cape Canaveral...Not much QSB if any at all...Only in the Winter months...

[K1JJ]

There used to be a midday net (noon) eastern on 1.845 here in FL where I have several times worked into coastal NC on slop bucket.  Both stations running abt 500 w and using inverted L's... I am located about a mile from the ocean near Cape Canaveral...Not much QSB if any at all...Only in the Winter months...

Hi Mark,

Thanks for the info.

Only in the Winter months?  You mean you could only propagate to NC during the winter months at noon OR did you mean the net was available only during the winter?  ie, what I'm wondering is if it was groundwave, it wud be all year 'round prop regardless of season, I think....

T

[Bill, KD0HG]

Tom, I've got the exact info you seek at home...
A chart of groundwave vs. frequency.
Even across the BCB, there's a trememdous difference
between groundwave coverage on 540 vs. 1700 KC.
Ground conductivity and dielectric constant, in addition to frequency,
plays the major role in groundwave coverage.

The FCC has issued a range of charts of ground conductivity vs.
frequency vs. distance vs. signal strength in Part 73.184.

At 1700 KC, given the same TX power and antenna efficiency,
true groundwave goes ~ half the distance as it does at 540 KC.

I don't know if you're mixing up a space wave (direct line of sight)
with true groundwave, which is always vertically-polarized...

In any case, you *cannot* transmit true groundwave with a horizontally-polarized
antenna. You have to use a vertical,
But you can cover some shorter distance via spacewave.
This is why AM BCB transmit antennas are always verticals.

..

[Glenn NY4NC]

Hi Tom;

Beacons are a great indicator of groundwave propagation below 1.6mhz. Back in the 1980's when we were doing experiments on the 160-190khz "lowfer" band, certain beacon stations could be copied at 75+ miles (daytime, winter months).

Good indicators below the broadcast band are the aero beacons (200-400khz) We found our vertical LF transmitting antennas worked best for pulling in LF beacons on receive. Horizontal wires were NG and small loops were not that great at hearing very weak signals compared to the big verticals. Of course nighttime is no good because there is skywave propagation on LF.

There seems to be a common belief that below 1.6 mhz there is substantial groundwave extending out many miles. How far and at what frequencies have you observed?  I think the time to tell is when the band is broke and long for local stations, just like 75M... 

73,
Tom, K1JJ

[W1RKW]

Hi Tom,

Very good question.

I don't know how this relates to your ground wave question but an observation I've seen between 75m, 160, and BCB is the amount of QRN that exists compared to each band.  75m seems to exhibit more atmospheric noise than 160 and BCB at those times when QRN on 75m is present. Why that is I'm not sure but I'm sure someone can expound on that.  But I think too  the groundwave on 75m has to be very short if non-existant.  I've listened to you on 75m with my bedside radio and there are times that your signal strength is bouncing all over the place or just plain low, very simular to what you've stated with some of your local QSO's, and you're less than 10 miles from me as the crow flies.

Bob

[K1JJ]

Tom, I've got the exact info you seek at home...
A chart of groundwave vs. frequency.
I don't know if you're mixing up a space wave (direct line of sight)
with true groundwave, which is always vertically-polarized...

Bill,

Yep, I think you're right about mixing ground wave with space wave. They seem to be used interchangably these days. 

So, true ground wave is what we talk about with vertical antennas and BC service, whereas space wave is what we refer to when talking about most ham HF and horizontal stuff.

Yes, I would like to see those freq vs: groundwave plots. It also does seem logical that the better ground makes it propagate better.

As for space wave...  if you refer to my comments in the first post about 75M, it appears that the space wave is very short on 75M.  However, on 6M it is very long. For example, on 6M I can talk out 40 miles with S9+50 signals both ways and they are constant each night  - within 2 db every night. Farther away, like 60 miles plus, the signals seem to get tropo enhanced some nights by up to 10db, but never less than a certain "space wave " minimum value.

So, it appears to me that as you go up in frequency, the space wave gets stronger, whereas the ground wave gets weaker and vice versa.  And for 160 -10M work, we should generally be calling it space wave, not ground wave....

Does this sound correct to you?

T

[Jim, W5JO]

The longer the wave the better for reflection off the ground.  There are no hard and fast rules but Bill has the answer.  The space wave decreases as to the square of the distance.  Ground wave is attenuated by poor ground conductivity at the frequency of interest and location.

I have seen broadcast stations on the same frequency in different parts of the country that have different size coverage patterns due to the ground over which the wave in traveling.

Sky wave comes into play on the BCB when conditions are as they are now.  The inosphere has no ripples for lack of sunspot activity therefore reflect better.  Right now here, the skywave is a factor on BCB, 160 and 75 until about 10 AM.  BCB begins to fade first and the frequency moves up with time.  The skywave returns to 75 about 3-3:30 in the afternoon.  This transistion is fairly rapid.

If Bill posts those charts, then you will have a good idea of ground wave vs frequency.  They are damned accurate too.

[KB2WIG]

The groundwave propigation is great on the low bands. A friend of mine did some work on 2997m with a vertical located in the FLA keys. He said the problem was too much  propigation. The noise propigated along with the signal. Noise from everywhere.  The noise coupled with the bandwith he needed didn't work well enough for what he needed to do. He did like the atmospheric noise though; sounds like birds chirping, whales moaning etc...    klc

[Jim, W5JO]

[
Bill,

Yep, I think you're right about mixing ground wave with space wave. They seem to be used interchangably these days. 

So, true ground wave is what we talk about with vertical antennas and BC service, whereas space wave is what we refer to when talking about most ham HF and horizontal stuff.

Yes, I would like to see those freq vs: groundwave plots. It also does seem logical that the better ground makes it propagate better.

As for space wave...  if you refer to my comments in the first post about 75M, it appears that the space wave is very short on 75M.  However, on 6M it is very long. For example, on 6M I can talk out 40 miles with S9+50 signals both ways and they are constant each night  - within 2 db every night. Farther away, like 60 miles plus, the signals seem to get tropo enhanced some nights by up to 10db, but never less than a certain "space wave " minimum value.

So, it appears to me that as you go up in frequency, the space wave gets stronger, whereas the ground wave gets weaker and vice versa.  And for 160 -10M work, we should generally be calling it space wave, not ground wave....

Does this sound correct to you?

T

T all antennas vertical/horizontal or multi phased (I forget the exact name) will have ground wave.  Because of the lay of the magnetic field the amount reflected with a vertical is more intense than horizontal for the incident wave.  Once reflected the wave will have a 180 degree phase reversal.  Fades from reflected waves are the result of the reflected wave arriving as it goes through 90 degrees.

With the space wave, it will travel a little further on the lower frequencies over the horizon than the higher frequencies, however on the upper bands (6, 2, and 1 1/4) the waves are so small compartively that they will reflect off objects, a lot of moisture in the air, meteor trails, etc.  Generally on the upper bands the space wave is to the horizon, but on 75 is is a bit beyond.  The longer wave is not easily bent by water or reflected by objects as the smaller wave.

The space wave is the unobstructed wave emitted into the air that can be received directly from the transmitting antenna or by reflection from the ionosphere, not that wave that is reflected from the gound.  Ground waves are much like skipping a stone across the water and eventually attenuate fully.  Frequencies much above 7 Meg do not have much groundwave because of absorbtion by the earth.  At about 5 Meg the ground wave is insignifcant for our purposes and one must rely on the space wave and reflection (depending on power level and antenna height/efficiency).  The multi hop signal is a space wave that has struck the ionosphere directly from the antenna, been refelcted to the ground then reflected back to the ionosphere a second or third time.

Take 40 meters in the day time and the ground wave probably mayl be shorter than the space wave which may only be about 30 miles.  But on 75 the ground wave will be longer exceeding the space wave for a few miles.

By the way, you have been asking thinking questions lately, what gives?

[K1JJ]

1) With the space wave, it will travel a little further on the lower frequencies over the horizon than the higher frequencies,

2) The space wave is the unobstructed wave emitted into the air that can be received directly from the transmitting antenna or by reflection from the ionosphere, not that wave that is reflected from the gound.  

3) By the way, you have been asking thinking questions lately, what gives?

Great information, guys - thanks!

Jim, a few comments....

#1 about the space wave traveling farther on lower freqs...   So, why is it on 6M [with no skip, just space wave] the local guys are ALWAYS the same strength at +50 over S9, 40 miles away with no variation night to night, but on 75M when the ionospheric skip goes away and gets long , I cannot copy any local guys within 40 miles? They're like S5 in the noise? Same radio, same S meter too, using a 6M transverter. It seems like the space wave is way stronger on 6M???

#2 about the space wave and reflected ground signal...  how about the reflected part of the wave that comes off the antenna, hits the ground and get combined in phase with the intial wave to add 6db to the signal, ie ground reflection enhancement in the near field? Or are you referring to ground reflections AFTER this happens?  Also, I didn't know the space wave is also one that has hit the ionosphere and came back down again.  Thought it was just a pure line of sight situation...??

#3 Why am I axing a lot of questions?  Oh, partly cuz I'm currently working on related projects and need to know to proceed, or else someone else axed a question that I cannot answer, so it gets axed here. It's a wonderful way to get everyone thinking and better edumacated, don't ya think? And, the archives are gonna look real fat in the future...

73,
T

[Bill, KD0HG]

Guys, I only know enough about this to make me dangerous.

True groundwave at MF is when the wave propagates itself
along the earth's surface like a signal on a transmission line.
The earth's surface acts as a conductor at low frequencies which
becomes a dielectric and lossy at shortwave frequencies.
The field of a true groundwave is attenuated by losses in the ground,
in a way exactly like feedline loss. It would seem to be less than square law loss
at VLF frequencies.

Tom, spacewave is attenuated by square law, not by the
conductivity of the ground beneath and it's debateable whether
horizontal or vertical  is better. There's that little of a difference
with spacewave.

Atmospheric nd optical effects come into play on HF and up. You got yer tropo enhancement,  you got yer ducting and etc.

The fact that strong groundwave exists at low frequencies obscures the fact that
spacewave also exists on VLF-LF as it does on higher frequencies.
Square law again.

Check out this excellent  groundwave propagation program. It runs as a DOS
window. Enter all the values, then you can easily scroll the frequency
to see what happens when you QSY from VLF to HF.

http://www.smeter.net/propagation/grndwav3.php
Scroll to the bottom and download GrndWave3.exe.

..

[Jim, W5JO]

Danerous Huh Bill?  T, I defer to Bill's answer he explains your two questions very well.  My typing fingers are getting tired and I want to work some ground/skywave on 160 tonight.  See you there.

[W3SLK]

I might as well weigh in on this too. Joe, N3IBX and I worked handily on 1.885 at 1:30PM a few weeks ago. We both used horizontally polarized aerials and 100 watt DX-100's. We are about 175 miles as the crow flies. We worked each other Q-5 without any problems. What I would compare it to would be like working into a 2M repeater. It was very quiet. The one strange point is that the band did exhibit some QSB. His signal would dive just long enough for me to lose a word or two but would be back up very quickly. The copy was tons better since 1) you weren't dealing with any of the band 'hash', 2) No QRM to speak of. The only thing I heard and what I suspect was the clicking of an electric fence.

[Bacon, WA3WDR]

Generally, ground wave propagates better at lower frequencies, and it propagates best over salt water.  There are charts in Terman's Radio Engineer's Handbook (1943) that show the effect very clearly.

Interesting point about 6-meter space wave propagation.  I wonder if we put our antennas up at 1250 feet, would 75 meters work more like 6 meters does?  Our 75 meter antennas are all within 1/2 wavelength of ground.  If we did that at 6 meters, I suspect that we would not get much better local coverage.

There is a polarization tilt with vertically polarized ground wave signals.  Propagation is slightly slower at the surface, probably because of resistive and dielectric effect of the ground surface.  The wave tends to tilt forward because of this drag against the surface, and the propagating wave responds by curving downward toward the ground, because the electric field is bent forward and curved near the ground, and the electromagnetic wave propagates perpendicularly to its electic and magnetic field components.  I think that this causes a diffractive dispersion effect that pulls signal energy down from the space above the ground, and drives it into the ground.  This is probably the reason that there is a lot of attenuation of the space wave at low angles of radiation at HF, regardless of antenna polarization.  Lossy ground in particular tends to reduce radiation at low angles a lot.  But this dispersion would probably have much less effect at heights beyond a half wavelength above the ground, so if we got 75 meter antennas up really high, we would probably get pretty good spacewave communication.  I think this would have to be tested by aircraft.  Hmmm, a balloon loop...

On 75 meters, I agree that ground wave is pretty much gone by the time you get 5 or 10 miles away over land.  But over salt water, it stretches further, maybe 20 miles or more.  In some daytime tests I ran on 1.71 MHz some years back, I lost the ground wave within about 20 miles of the transmit site on land, but I could receive it, weakly, hundreds of miles away over water (Deer Park, Long Island to Ocean City, Maryland, pretty much a salt-water shot).  Probably there is less polarization tilt over salt water, causing less dispersion and loss.

[K1JJ]

Interesting point about 6-meter space wave propagation.  I wonder if we put some our antennas up at 1250 feet, would 75 meters work more like 6 meters does?  Our 75 meter antennas are all within 1/2 wavelength of ground.  If we did that at 6 meters, I suspect that we would not get much better local coverage.

Hmmmm...   a very interesting answer, Bacon.  Maybe so. There certainly would be many angles in that 75M pattern at 1250' high, including very high ones along with the lowest at about 3.5 degrees..

Yes, the takeoff angle of my 6M yagi at 195' is about 1.75 degrees with nothing in the way.  Whereas, the 75M dipole for local work is at 80', or a takeoff angle of about 45 degrees or so. Big difference for line of sight work. Much more energy at the zero degree horizon.

What also reinforces that idea is that on 6M, the space wave [line of sight] coverage is directly propotional to the height above ground out to about 120 miles.  Guys with low 6M Yagis cannot hear very well in comparison out until GREATER than 120 miles compared to the high Yagis. But after 120 miles or so, the two antennas get reasonably close cuz of the tropo bending/enhancement. The big edge disappears. 

Notice this 120 miles is past the curvature of the Earth. There seems to be some bending going on
until the tropo scatter evens things out.

I did read yesterday that a spacewave will propagate farther when "it is moving higher above ground".  Another way of saying the higher the ant, the better the line of sight, I suppose.

T

[WB2RJR]

Tom,

At my Colorado QTH I have coverage all the time on 75 to Greeley (60miles), Fort Collins (70 miles), and to Cheyenne, Wy (120) miles with good signals. I get all the Cheyenne TV stations with my rabbit ears. QTH is at 7185 ft. and the ground slopes off to the north northeast to 5674 ft in about 1 1/8 miles. I can see the lights of Ft. Collins and Greeley at night so this is line of sight not ground wave. North northeast is my path to Europe and with my LP at 70 ft I can hear and work Europe as the band opens 45 to 75 minutes before my friend on the plains can hear anything with his KT 34XA at 140 ft. It's a great spot for pounding a signal into Europe or Asia over the pole. If I could just get rid of the two mountains to my east and southeast it would be a perfect location.

73, Marty

[Tom WA3KLR]

One of my engineering handbooks (Reference Data for Radio Engineers, 5th Ed. p. 26-4) has a chart for ground loss, but it shows curves for 10 kHz to 3 MHz. only.

Here is a related chart from Antenna Engineering Handbook by Jasik; p.33-19.  If you pick 3 miles as a reference point for 75 meters ground wave limit for example, this is a level of about 65 dB above 1 uV/meter.  Following this level left to the 29 MHz region yields about 0.6 miles for the same signal level.

I hope this chart is a help.

[K1JJ]

Yeah, that's a pretty neat chart, Tom.

It appears that going from 3mhz to  0.4mhz gives about five times farther ground wave.

It looks almost like a log curve vs: freq.

I was suprised to see you must get below the BC band before the curve really takes off. It's like 10 miles at 3mhz, 50 miles at 0.4mhz  and 100+++ miles down lower for a given signal level.  So, as Bill said, there is a big differnce between 1.6 and 0.540 mhz on the BC band.

I guess there's not a huge difference throughout the 75M -10M band for ground wave raw miles.  < 5-10 miles gnd wave for a modest signal level.

Tnx, OM.

T

[Tom WA3KLR]

And just for kicks, here is the ground loss chart from Reference Data for Radio Engineers, 5th Edition, page 26-4. 

Curves for 10 kHz to 3 MHz :

[K1JJ]

Hmmm..... 30db improvement difference from 4mhz to 1.8mhz. and another 30 db improvement from 1.8 to the middle of the BC band.

You can see the tremendous ground loss improvement that the VLF guys enjoy. It's like almost 100 db better ground propagation down there...

T

[Steve - WB3HUZ]

JJ:

Notice this 120 miles is past the curvature of the Earth. There seems to be some bending going on until the tropo scatter evens things out.

This is called the 'radio horizon.' It exceeds the visible horizon due to scattering (mostly). If you assume the earth is a smooth surface (of course it's not) you can approximate the distance (in miles) to the radio horizon by

R = 1.415 x sqroot (h), where h is the antenna height feet.

For a comms system, where two antennas are involved, you must consider the height of both antennas. So you get something like

Rt = [1.415 x sqroot (h1)] + [1.415 x sqroot (h2)]


So, can you make a contact with a guy 100 miles away who has a 50 foot high antenna (let's say yours is at 150 feet)?

Rt = [1.415 x sqroot (150)] + [1.415 x sqroot (50)]

Rt = [17.33] + [10]

Rt = 27.33 miles.

So the answer is no. But you've already made contacts at much greater distances than this. What gives? First, the above is an approximation (doesn't consider knife-edge diffratction, and such). Second, the contacts may not have been truly line-of-sight/space wave (other propagation types involved). And finally, I'm betting your antenna is much more than 150 feet high, when terrain is considered (you're at the top of a pretty big hill). That's where things like HAAT - Height Above Average Terrain come into play. In your case, the HAAT is MUCH more than 150 feet!

[K1JJ]

Steve,

I just got an email requesting a forward to the "HUZman / Big Country":

It reads:

" I's gots a PDL quad on the roof of the apartment building on the tenth floor here in Hartford. Bout 92' high. I wanna talk to the Terminator down in Philly. He's gots a Moonraker II on a tripod on the top of his trailer at 17'. How much heat we gonna need for the trip?"  -  Mad Dog


Can you help this guy out?

BTW, TNX for the info on line of sight.

T

[Steve - WB3HUZ]

Answer:

He'll never do it on any channel I'm on. When I put the maul down, all you hear is me - WHIRLWIDE.

Get these mud ducks outta here!

[k4kyv]

Hmmm..... 30db improvement difference from 4mhz to 1.8mhz. and another 30 db improvement from 1.8 to the middle of the BC band.

160m mobile used to be popular in some larger midwestern cities such as Chicago and Cleveland, back before the days of 2m CB.  Hams comfortably talked across town mobile-to-mobile during morning and evening rush hour.

According to an old ARRL Mobile Handbook (they stopped publishing those once almost all mobile installations had become equipped 100% with off-the-shelf appliances and hardware), 160m was a better band for local mobile operation because the improvement in groundwave progagation more than made up for the loss of antenna efficiency when going from 75m to 160m mobile, using the same length radiator.  Plus in those days 160m power limits were severely limited, and mobile contacts were less likely to be obliterated by high powered fixed stations.