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Well, a 6 dB boost would double your range, IF you aren't
hitting the limits imposed by your radio horizon. _____________ Clarification: the coverage AREA doubles for the above situation, but the "range," or distance from the transmit antenna to a given field strength value increases only by about 40%. Here are the numbers, using the FCC's F50,50 curves for UHF NTSC TV propagation. 50W ERP from 100 feet above average terrain: 60dBuV/m at 2.99 miles Coverage area within the 60dBuV/m contour = 28 sq miles 200W ERP from 100 feet above average terrain (a 6dB ERP increase from the above example): 66dBuV/m at 2.99 miles 60dBuV/m at 4.2 miles Coverage area within the 60dBuV/m contour = 55.4 sq miles The radio horizon for these examples is located about 14 miles from the antenna site (at a 0.15 degree depression angle). RF Visit http://rfry.org for FM transmission system papers. |
"KF6HHS" wrote:
I stand by my statement, " 6dB doubles your range... Anyone who has done path analysis knows that 6dB doubles the range. Check into it - you might learn. _____________ I've checked, thanks. The field strength values I posted are based on empirical data used by the FCC to determine coverage range, and protection ratios for FM & TV broadcast stations. The same physics applies to "hams" as to broadcasters. The free-space path loss formula over a reflection-free path gives different results. But, as the original post asks " Is it worth it? Will I notice?," the real-world values from the FCC curves will give more applicable answers. Verify my numbers and conclusions for yourself at http://www.fcc.gov/mb/audio/includes/curves.html . You might learn g. RF |
KF6HHS wrote:
"I stand by my statement: 6 dB doubles your range." The "Sommerfeld formula" is ancient and accepted. It says: Ground-wave field strength = (A) Eo / d Eo = field strength at the surface of the earth at a unit distance from the transmitting antenna, neglecting earth`s losses d = distance to the transmitting antenna A = factor taking into account ground losses If the earth is perfect, the above reduces to: volts/meter = Eo / d assuming the right scale factors. At twice the distance, the field strength over flat earth is halved. The resulting current is also halved. Thus, the power, their product, is quartered. That`s a 6dB change from doubling the distance. On the other hand, if you want to produce the same field strength at twice the distance, you must use 4X the power by the Sommerfeld formula. Best regards, Richard Harrison, KB5WZI |
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Richard Clark is correct. The FCC family of propagation curves shows
greater attenuation than results from signal spreading into an ever enlarging volume. However, these curves also include an inverse distance line which is the 6 dB per doubled distance line. Its drop, make that decline, only derives from the growth in volume the fixed amount of expanding signal fills as it propagates. Best regards, Richard Harrison, KB5WZI |
A long time ago, when there was not so much man-made noise, I found that in
the almost-flat-country at the extreme edges of coverage from a base station to a mobile station, the rate of decrease was roughly one db per statute mile. This was in the 160 MHz range. The mobile is so far away from the base that the received signal is "noisy." I am considering rural locations and a terrain without significant hills. On the average, +3db of power at the base provided another 3 miles of (poor quality) coverage. More often than not, coverage was limited by the transmitter power of the mobile and the noise level at the base! The question asked can start to be answered when one knows the value placed on increased coverage. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: |
On Sat, 13 Nov 2004 12:35:32 -0500, "J. Mc Laughlin"
wrote: A long time ago, when there was not so much man-made noise, I found that in the almost-flat-country at the extreme edges of coverage from a base station to a mobile station, the rate of decrease was roughly one db per statute mile. This was in the 160 MHz range. The mobile is so far away from the base that the received signal is "noisy." I am considering rural locations and a terrain without significant hills. On the average, +3db of power at the base provided another 3 miles of (poor quality) coverage. More often than not, coverage was limited by the transmitter power of the mobile and the noise level at the base! The question asked can start to be answered when one knows the value placed on increased coverage. I'll bet I can get good reliable converage to a 100 miles with a 5 watt HT and a rubber duck with todays receivers. 50 to 75 mile coverage to mobiles. It's worked on 52 simplex every time I've tried it. Fasten the belt clip to the strap above the arm rest with the rubber duck sticking straight up into the big window, Hook a boom mike and ear piece to the HT and put my ANR head set over it. Call CQ and darn near get a pile up. Ain't nothing like a good tall antenna. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com 73 Mac N8TT |
"KF6HHS" wrote in message ... 150 mhz = 6.913 db improvement 450 mhz = 7.756 db improvement Antenna tip 15 feet higher Now here's my question - will I notice the improvement enough? I've had several OM's tell me that on SSB, CW or HF I would but not on 2m/440 simplex and repeaters. Ken KG0WX Well, Ken maybe your "OM's" didn't eat their Wheaties. A 6dB improvement means you have quadrupled your ERP over your existing system. You have also increased the distance to your radio horizon with the increse in antenna height. Why they would say you won't notice an improvement is beyond me. In plane language here are a few things just a 6dB improvement mean. You can reduce your radios Tx power by a factor of 4 and have the equivalent ERP, 6dB doubles your range Tx and Rx (within the limits of your stations LOS - line of sight). Stations that were noisy will now be full quieting, be it simplex or repeaters you work. In even simpler terms, "night and day". What are you waiting for? Regards, Hugh KF6HHS Retired, now life moves at my pace. please note spam filter Well, I did it. I changed plans at the last second, though, going for the Hustler CG-144 monobander with radial kit. Instead of paying $200 for the GP-9, I paid $27 and got almost as much gain. After figuring my old antenna's gain - coax - connectors, I figured the new coax (Flexi 4XL) and antenna. The new antenna is 5 feet higher and my system gained 3.940 db. My S-meter on my 2 meter rig is stingy, esp. around S8 where it has an almost logritmic scale action. Still, several repeaters went from S3 to S5 and several went from S7 to S9. One repeater remained S1 but it's noise factor went from 50% quieting to 70% quieting. Turns out it probably was a good decision - the Hustler has 5.2 dbi gain and the tip is at 42'. I'm just stating to get intermod at this level of performance (I live between a hospital & Boeing). I'm convinced if I had gone with the GP-9, I would have serious intermod problems (plus my wallet would be $170 lighter) plus raising it would have been MUCH harder. Thanks to all who offered advice on this topic - You guys rule! 73's de Ken KG0WX |
Well, I did it. I changed plans at the last second, though,
going for the Hustler CG-144 monobander with radial kit. Instead of paying $200 for the GP-9, I paid $27 and got almost as much gain. After figuring my old antenna's gain - coax - connectors, I figured the new coax (Flexi 4XL) and antenna. The new antenna is 5 feet higher and my system gained 3.940 db. My S-meter on my 2 meter rig is stingy, esp. around S8 where it has an almost logritmic scale action. Still, several repeaters went from S3 to S5 and several went from S7 to S9. One repeater remained S1 but it's noise factor went from 50% quieting to 70% quieting. Turns out it probably was a good decision - the Hustler has 5.2 dbi gain and the tip is at 42'. I'm just stating to get intermod at this level of performance (I live between a hospital & Boeing). I'm convinced if I had gone with the GP-9, I would have serious intermod problems (plus my wallet would be $170 lighter) plus raising it would have been MUCH harder. The worth it question seems to be that you spent $ 27 for a net gain to get one repeater to go from about 50% to 70 % quieting. The other repeaters were peobably full quieting so you would not gain anything on them even if you spent the full $ 200. Whe 'worth it " will come when you are making contacts that you did not make with what you already had. |
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