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K1YW wrote:
"Artsci takes into account: To properly estimate a signal`s range, you must have a few important figures---- Frequency / Band Transmitter power (in watts) Antenna height (from sea level) Antenna gain (net after coax loss) As a practical matter, first you must have a line-of-sight path. Then you can worry about path attenuation, gains, losses, transmitter power and receiver sensitivity. Attenuation between stations with an obstructed path (including earth bulge) rises so rapidly with the obstruction that non of the other factors matters except in the case of brute force communication, such as atmospheric scatter. Best regards, Richard Harrison, KB5WZI |
Terman also says the radio horizon as seen from a ground-mounted vertical
antenna is at distance of - 50 / Cuberoot(FreqMhz) miles. This does not mean the ground wave suddenly weakens at this distance but that Earth curvature and atmospheric refraction begin to have a significant effect on ground-wave propagation. At MF and LF, useful ground-wave propagation can occur at distances considerably greater than the radio horizon. At HF the skywave can provide stronger signals. ---- Reg, G4FGQ |
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K1YW wrote:
"So Artsci should help him (KC5CQA)." 50-watt radios will talk with plenty of exess fade margin over any line-of-sight path from a 100-foot tower to any land mobile in the two-meter band. Beyond line-of-sight, VHF propagation is kaput because the signal does not follow earth curvature as Reg`s low and medium frequencies do. Over smooth earth or sea, the horizon is sq rt of 200 from a 100-foot high antenna. That is about 14 miles. Add 4 or 5 miles of range due to the mobile antenna height and that is near the maximum range. 5 watts, 100 watts, or 500 watts make very little difference in range. Range is extended with increased power very slightly. There is some noise reduction. In my experience, I found it advantageous to use 50-watt mobiles and 500-watt base stations. This is because the mobile is often in a noisier environment than the base station. Obviously the path length is the same in both directions in this VHF application. The dominant requirement in VHF communication is a line-of-sight path. Once that is obtained, all else is secondary. Most of the microwave stations I`ve put in have 100-milliwatt transmitters and these produced 30 dB fade margins on paths of more than 20 miles. For land mobile VHF service, you usually have no significant antenna gains, but you also have significantly lower path and transmission line losses, higher receiver sensitivities, and higher transmitter powers. Received carrier power to produce full quieting in a good receiver is very small indeed. This makes line-of-sight the only significant requirement for single-channel, single-hop VHF communications. Noise is cumulative, so for a multi-hop system, big signal surplus is required on each hop to supress noise to make the cumulative total acceptable. Best regards, Richard Harrison, KB5WZI |
There is almost always some kind of enhanced propagation. With 50W SSB to a
10 element 2 meter beam at 40 feet, 90% of the time my range is 75 - 100 miles when talking to another base station. I don't think they all have 1000 foot towers. Tam/WB2TT "Richard Harrison" wrote in message ... K1YW wrote: "So Artsci should help him (KC5CQA)." 50-watt radios will talk with plenty of exess fade margin over any line-of-sight path from a 100-foot tower to any land mobile in the two-meter band. Beyond line-of-sight, VHF propagation is kaput because the signal does not follow earth curvature as Reg`s low and medium frequencies do. Over smooth earth or sea, the horizon is sq rt of 200 from a 100-foot high antenna. That is about 14 miles. Add 4 or 5 miles of range due to the mobile antenna height and that is near the maximum range. 5 watts, 100 watts, or 500 watts make very little difference in range. Range is extended with increased power very slightly. There is some noise reduction. In my experience, I found it advantageous to use 50-watt mobiles and 500-watt base stations. This is because the mobile is often in a noisier environment than the base station. Obviously the path length is the same in both directions in this VHF application. The dominant requirement in VHF communication is a line-of-sight path. Once that is obtained, all else is secondary. Most of the microwave stations I`ve put in have 100-milliwatt transmitters and these produced 30 dB fade margins on paths of more than 20 miles. For land mobile VHF service, you usually have no significant antenna gains, but you also have significantly lower path and transmission line losses, higher receiver sensitivities, and higher transmitter powers. Received carrier power to produce full quieting in a good receiver is very small indeed. This makes line-of-sight the only significant requirement for single-channel, single-hop VHF communications. Noise is cumulative, so for a multi-hop system, big signal surplus is required on each hop to supress noise to make the cumulative total acceptable. Best regards, Richard Harrison, KB5WZI |
Tam, WB2TT wrote:
"There is almost always some kind of enhanced propagation." True. It is also true that a 10-element beam and high power extend transmission range. Terman has eqn. (22-7b) on page 820 of his 1955 edition: "Radio horizon distance in miles = sq rt 2h Again, h is in feet." Terman also says: "In the special case of the standard atmosphere, k = 1.33 and the horizon distance becomes, miles = sq rt 2h." 1.33 means the earth`s radius appears as 4/3 the actual value.due to atmosphere causing the radio horizon to be more distant than the optical horizon. On page 825, Terman says: "Fading is most pronounced when the received signal is much weaker than the free-space value for the distance involved. Thus fading is usually greatest near the radio horizon and in the shadow zone, and tends to be small when a "good" optical path is present." My experience agrees with Terman. We all know that VHF propagation does not always follow the simple rules. My contention is that path clearance outshines other considerations in determining "How far can an antenna see?". Terman`s eqn. (22-7b) is the usual answer. Best regards, Richard Harrison, KB5WZI |
O.K. CAN YOU HEAR ME NOW ?
"Tarmo Tammaru" wrote in message ... There is almost always some kind of enhanced propagation. With 50W SSB to a 10 element 2 meter beam at 40 feet, 90% of the time my range is 75 - 100 miles when talking to another base station. I don't think they all have 1000 foot towers. Tam/WB2TT "Richard Harrison" wrote in message ... K1YW wrote: "So Artsci should help him (KC5CQA)." 50-watt radios will talk with plenty of exess fade margin over any line-of-sight path from a 100-foot tower to any land mobile in the two-meter band. Beyond line-of-sight, VHF propagation is kaput because the signal does not follow earth curvature as Reg`s low and medium frequencies do. Over smooth earth or sea, the horizon is sq rt of 200 from a 100-foot high antenna. That is about 14 miles. Add 4 or 5 miles of range due to the mobile antenna height and that is near the maximum range. 5 watts, 100 watts, or 500 watts make very little difference in range. Range is extended with increased power very slightly. There is some noise reduction. In my experience, I found it advantageous to use 50-watt mobiles and 500-watt base stations. This is because the mobile is often in a noisier environment than the base station. Obviously the path length is the same in both directions in this VHF application. The dominant requirement in VHF communication is a line-of-sight path. Once that is obtained, all else is secondary. Most of the microwave stations I`ve put in have 100-milliwatt transmitters and these produced 30 dB fade margins on paths of more than 20 miles. For land mobile VHF service, you usually have no significant antenna gains, but you also have significantly lower path and transmission line losses, higher receiver sensitivities, and higher transmitter powers. Received carrier power to produce full quieting in a good receiver is very small indeed. This makes line-of-sight the only significant requirement for single-channel, single-hop VHF communications. Noise is cumulative, so for a multi-hop system, big signal surplus is required on each hop to supress noise to make the cumulative total acceptable. Best regards, Richard Harrison, KB5WZI |
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