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Will an antron 99 Roof Mounted get 41 Miles???
- Thread starter DualAntennas
- Start date
Old school R.O.T. - Rule of Thumb for distance to the radio horizon (note: many newer VHF/UHF calculators use a slightly DIFFERENT calculator, mainly I suppose because they are strictly VHF/UHF) is:
1.415 X the Square Root of the FEEDPOINT height AGL (Above Ground Level) of the antenna = distance to the radio horizon. So, for example,
If your A99 is mounted at 25',
1.415 X 5 (which is the square root of 25) = 7.075, or roughly, 7 miles to the horizon. Does that mean you can only work a 7 mile radius? NO, because the OTHER antenna ALSO has it's OWN radio horizon.
So, if the station at the Flying J ALSO has an antenna at 25', then they too have a 7 mile horizon, which you must add to your OWN, for a total RELIABLE comms distance of: 7.075 + 7.075 = 14.15 miles RELIABLY (in the real world, these numbers may be assumed to be MINIMUMS, therefore, you are likely to communicate up to 50-100% FURTHER if unobstructed by hills, buildings, etc.)
So, to get @40 miles, two-way, each station will need radio horizons totaling (when added TOGETHER), 40 miles.
If, for example, you take your 25' A99 and move it to 100' and the Flying J stations does likewise, you are NOW:
Each at 14.15 to the radio horizon; and 14.15 + 14.15 = 28.30 miles. Given that the real world factors are 50-100% higher, you guys could therefore conceivably be 42-56 miles from one another and still communicate.
Now I realize that 100' is pretty much not 'doable', but perhaps 49 feet IS more of a real world height. If BOTH antennas get their A99's feedpoints (bottoms of the antennas) up to 49' AGL, the numbers would come out to:
1.415 X 7 = 9.905 miles X 2 (for both station's horizons) = 19.81 miles, which, in the real world, would probably give you guys 30-40 miles maximum distance.
So, BOTH of you guys need antennas at 50' or higher, if you want to make it "work."
Unfortunately however, the Flying J (as I understand it) is a Truck Stop, and as such, what we often find in Truck Stops is a lot of trucks with CB radios, some high powered, that you'll not likely be able to get over no matter how high you raise your antenna, you'll never develop the uV (millivolts) on the Flying J's receive antenna to overcome the near field of the many trucks transmitting (splashing/bleeding) on adjacent channels, not to mention electrical and/or impulse noises on his receiver.
My closest truck stop is only about 15 air miles away from me. My antenna (ABS1600) is less than 25' AGL at the feedpoint, and the truck stop (Imax 2000) is less than 50'. I have NO TROUBLE with them at NIGHT (when the skip is not rolling in and overpowering us), but have difficulty with hearing each other in the daytime. Our 'calcs' SHOULD be:
Me: 1.415 X 5 = 7 miles + Him: 1.415 X 7 = 10 miles = 17 miles RELIABLY.... but even still, since we're only 15 miles away, sometimes it works, and sometimes (i.e.: ionospheric propagation, local truck traffic, etc.) it doesn't. The fact that we have a Q-5 copy on one another at NIGHT, reinforces the validity of the calcs.
1.415 X the Square Root of the FEEDPOINT height AGL (Above Ground Level) of the antenna = distance to the radio horizon. So, for example,
If your A99 is mounted at 25',
1.415 X 5 (which is the square root of 25) = 7.075, or roughly, 7 miles to the horizon. Does that mean you can only work a 7 mile radius? NO, because the OTHER antenna ALSO has it's OWN radio horizon.
So, if the station at the Flying J ALSO has an antenna at 25', then they too have a 7 mile horizon, which you must add to your OWN, for a total RELIABLE comms distance of: 7.075 + 7.075 = 14.15 miles RELIABLY (in the real world, these numbers may be assumed to be MINIMUMS, therefore, you are likely to communicate up to 50-100% FURTHER if unobstructed by hills, buildings, etc.)
So, to get @40 miles, two-way, each station will need radio horizons totaling (when added TOGETHER), 40 miles.
If, for example, you take your 25' A99 and move it to 100' and the Flying J stations does likewise, you are NOW:
Each at 14.15 to the radio horizon; and 14.15 + 14.15 = 28.30 miles. Given that the real world factors are 50-100% higher, you guys could therefore conceivably be 42-56 miles from one another and still communicate.
Now I realize that 100' is pretty much not 'doable', but perhaps 49 feet IS more of a real world height. If BOTH antennas get their A99's feedpoints (bottoms of the antennas) up to 49' AGL, the numbers would come out to:
1.415 X 7 = 9.905 miles X 2 (for both station's horizons) = 19.81 miles, which, in the real world, would probably give you guys 30-40 miles maximum distance.
So, BOTH of you guys need antennas at 50' or higher, if you want to make it "work."
Unfortunately however, the Flying J (as I understand it) is a Truck Stop, and as such, what we often find in Truck Stops is a lot of trucks with CB radios, some high powered, that you'll not likely be able to get over no matter how high you raise your antenna, you'll never develop the uV (millivolts) on the Flying J's receive antenna to overcome the near field of the many trucks transmitting (splashing/bleeding) on adjacent channels, not to mention electrical and/or impulse noises on his receiver.
My closest truck stop is only about 15 air miles away from me. My antenna (ABS1600) is less than 25' AGL at the feedpoint, and the truck stop (Imax 2000) is less than 50'. I have NO TROUBLE with them at NIGHT (when the skip is not rolling in and overpowering us), but have difficulty with hearing each other in the daytime. Our 'calcs' SHOULD be:
Me: 1.415 X 5 = 7 miles + Him: 1.415 X 7 = 10 miles = 17 miles RELIABLY.... but even still, since we're only 15 miles away, sometimes it works, and sometimes (i.e.: ionospheric propagation, local truck traffic, etc.) it doesn't. The fact that we have a Q-5 copy on one another at NIGHT, reinforces the validity of the calcs.
Two things about that example. The equation only gives the distance to the horizon, it doesn't account for any 'bending' of the signal which is definitely something to consider with HF.
The other thing is that for an antenna to be able to receive a signal it's radiation pattern must -over lap- the transmitting antenna, not just that transmitting antenna's radiation pattern. It has to 'contact' the source of that received signal. There is a little bit of 'skootch' in that but not much. That 'skootch', or 'fudge factor' takes into account the signal 'density' at whatever distance in question. Signal density varies with distance. The lower that signal density the weaker the signal and visa-versa.
- 'Doc
(Please excuse the technical terms, 'skootch' and 'fudge factor', they account for various variations when dealing with HF.)
The other thing is that for an antenna to be able to receive a signal it's radiation pattern must -over lap- the transmitting antenna, not just that transmitting antenna's radiation pattern. It has to 'contact' the source of that received signal. There is a little bit of 'skootch' in that but not much. That 'skootch', or 'fudge factor' takes into account the signal 'density' at whatever distance in question. Signal density varies with distance. The lower that signal density the weaker the signal and visa-versa.
- 'Doc
(Please excuse the technical terms, 'skootch' and 'fudge factor', they account for various variations when dealing with HF.)
Because of terrain my horizon to the north-west used to be about 1/4 mile. I used to regularly communicate out to 50 miles with 12 watts pep and a four element yagi at 40 feet. That 40 feet was the elevation of the garden behind the house on the hill. Yep beaming straight into the hillside.With a groundplane the same distance was covered but with reduced signal strength. Those "distance calculators" are useless IMHO. I have never seen them come up with anything near reality.
If a signal is limited by the horizon, no 'bend' to is as VHF/UHF, then those calculators stand a chance. If there's any 'bend'/refraction to a signal, as with HF, those calculators are at -best- only a guess for 'line of sight' type stuff. That's just not very realistic/practical for HF. Even with VHF/UHF signals it's only a 'possibility', not a certainty. Too many variables for it to ever be 'exact'.
- 'Doc
- 'Doc