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I have 10 watt CB radio system & 0.64 lambda monopole antenna , I think it has a 5 dBi gain .

what is the maximum acheivable range by ground wave in an urban area ?

If I want to increase my range without increase the system’s power , can I make 10 elements antenna array and get another 10 dB gain above my 5 dBi ?

abduoman11
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1 Answers1

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First, a "ground wave" is difficult to estimate since it is so dependent on all kinds of things, most importantly frequency and second the conductivity of the ground (or, water). Buildings in an urban area can result in diffraction of the ground wave among buildings that can create strange areas of signal strength and signal weakness that are virtually impossible to predict without actual experiment.

The previous similar question (noted in the comments) is different from this one in frequency. So, I will answer for the US CB frequency (just under 28 MHz). For a 28 MHz signal, with all other features ignored, is about 5 to 7 miles (or, 8 to 11 km).

There is actually three different types of propagation considered as ground wave and they behave quite differently from each other which makes guessing at distance for ground wave to be even more difficult.

  1. Tropospheric Bending Ground Wave

This is a ground wave that travels in the atmosphere and ground itself is somewhat independent of the nature of the ground. It is included here because Tropospheric Bending has similar propagation to ground wave. This type of propagation is most notable in VHF and above frequencies so not much use to CB frequencies.

  1. Direct Line-of-Sight Ground Wave

This is similar to above in that the ground effects are not pertinent other then the fact that curvature of the surface of the earth limits the effective line-of-sight success. But, this is the most likely type of propagation the OP will see useful in an urban setting for CB (along with benefits of diffraction). For actual distance coverage, line of site computations can be estimated using either of the following approximate formula: $$ D_\text{miles} = 1.415 \sqrt{H_\text{feet}}\\[2ex] D_\text{km}= 4.124\sqrt{H_\text{meters}} $$

Where $H$ is the height of the transmitting (or, receiving) antenna. By including both transmitting and receiving antennas and computing for overlap of the two distance results you can determine the longer line-of-site propagation path available.

  1. Low-Frequency Surface Wave

I say low-frequency since this type of ground wave, that actually uses the conductivity features of the ground are most effective at lower frequency, or MF (~2 MHz) and under. This is the method used for submarine communications where propagation is measured in the 1000s of miles for the super low frequency. Note that in this case, since frequency is so low, actual information transmission is very slow, measured at only a few characters per second in some cases. Surface wave propagation for super low frequency requires humongous antennas so it is not a practical solution for hobbyists.

K7PEH
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  • 5-7 miles? How do you figure that, after a whole paragraph on all the things that can vary that figure, which is itself only a partial list, missing things like transmitter power, antenna gain, modulation, etc? – Phil Frost - W8II Oct 29 '14 at 19:08
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    I didn't figure it, I merely looked it up in the ARRL Antenna Book (see the figure 4-1, on page 4-2, of the 22nd Edition of the ARRL Antenna Book for Radio Communications). Also, transmitter power, antenna gain, and modulation does not really change the propagation other than the effectiveness of copying a signal which though important is actually a separate issue. I am assuming that the OP would consider the obvious impact of TX power, antenna gain, or modulation given the answers received. – K7PEH Oct 29 '14 at 19:57
  • That number from ARRL is only appropriate given some assumptions about transmitter power (CB has a legal limit) and modulation (AM and SSB for CB in the USA). I don't know why you think path loss (propagation) and "effectiveness of copying a signal" are separate things. Decreasing the path loss (by decreasing the path length, for example) by 10 dB has exactly the same effect as increasing transmitter power or antenna gain by 10 dB. -1 for misleading technical superstition and bad assumptions. – Phil Frost - W8II Oct 29 '14 at 21:21
  • you said the CB is only for line of sight , but I want really to propagate more further than line of sight with a medium to small antenna size without put the antenna at 1000 meters high !

    the second point ... you say the VHF can be propagated by troposcattered wave , that is a smaller antenna size, but you did not say how much it will be effective ?

     – abduoman11 Oct 29 '14 at 21:53
  • @abduoman11 -- If you have an antenna 1000 meters high then you have up to (assuming no intervening mountain tops or other obstructions) roughly 130 km to the horizon which I compute using the formula given above. If you need to communicate more than that without wires then you need to make use of HF frequencies plus the Ionosphere and the skip you get which of course is not line-of-sight. And, even given that, nothing is guaranteed. Actually, another method you might consider is VHF and a satellite repeater in LEO. – K7PEH Oct 29 '14 at 22:32
  • @PhilFrost -- "Misleading technical superstition" -- you're kidding right? Where is the superstition? And, what are my bad assumptions --- I actually assumed as little as practical. I assumed nothing of the actual TX/RX capabilities such as power, gain, etc. because they are assumptions so don't count in my opinion. I am out of here. – K7PEH Oct 29 '14 at 22:44
  • @K7PEH I sticked in my question to ground wave because the I want covering all target area , not skipping to one location.

    I know NVIS is useful without skip, but it is not stable all the time and I should change frequency every some hours .

     – abduoman11 Oct 29 '14 at 23:04
  • @abduoman11 -- I am very curious about your "application" of using this ground wave and maybe some detailed descriptions of your operating parameters. A Well posed question is something like "I am wanting to do such-and-such and I think ground wave is my best solution, please help or give advice on my problem". – K7PEH Oct 29 '14 at 23:18
  • 5 dBi Tx antenna , 10 w Tx , data type: voice . CB of course. target is mobile about 80 - 200 km range . – abduoman11 Oct 29 '14 at 23:24
  • @abduoman11 -- your application is not practical. It is possible to get some kind of weird propagation effect and reach 80 to 200 km but this is not something you can rely upon. Indeed, given skip and this time of the Solar Sunspot cycle you are more likely to have skip of 3000 km. Two weeks ago, I had a QSO with a station in Hawaii (big island and my QTH is Seattle area) on 28.040 MHz with CW mode and 10 watts (using Elecraft KX3). But, the 10-meter band is likely on the downside of performance like this (sunspot cycle waning). – K7PEH Oct 30 '14 at 00:26
  • The superstition is that you seem to somehow believe "propagation" and "effectiveness of copying a signal" are somehow different things, or that if I transmit with 100 kW the ground wave will propagate the same distance as if I transmit with 1 mW. In reality, the wave propagates forever, and the only limiting factor is our ability to detect it. The "5-7 miles" figure is based on a lot of assumptions that weren't in the question nor stated in the answer. – Phil Frost - W8II Oct 30 '14 at 12:53