73's & greetings to all readers. Using Google earth, I've obtained coordinates for my QTH and for a location where I will install a second station, approx 1,500 miles away. From a government website, I obtained the declination between true vs magnetic north (it is negative at both sites: 3*17' west at QTH and 12*34'west at the DX). I know how to set the compass to the azimuth shown on Google and then set the antennas at each location to correspond, however, I'm starting to question whether I must make other adjustments to compensate between true north and magnetic north. Will somebody explain if I need to compensate for the difference between magnetic vs true north in order to have both antennas 'facing' each other? I know the beam will forgive a 3 degrees error, but not so sure about the 12 degrees. Both antennas will be moved by an 'armstrong' rotor (fixed).
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Setting azimuth/ bearing on directional antennas
- Thread starter Wire Dawg
- Start date
You don't describe the antennas very much, but unless you have more than four or five elements on the boom of each antenna, I wouldn't worry about ±20°. I'd be more concerned about the frequency and time of day.
Like Beetle said, tell us what the antennas are and and the frequency or band in question so we can help you better. As long as you set the antennas up as close as you can with a compass you should be fine anyway.You said you already know about the magnetic declination between true north and magnetic north and that is fine. If you use Google Earth you can draw a path from one location to the other and it will show you the proper bearing. In any case due to the curvature of the earth there are things to consider when pointing an antenna. The absoulute worst case is when looking due east or due west and over a 1500 mile path the difference is only 9 degrees which is insignificant. You said "I know the beam will forgive a 3 degrees error, but not so sure about the 12 degrees." On that I beg to differ as I think you made a mistake. You will never see such a narrow beamwidth on HF or even VHF. Those kind of beamwidths only start to come into play on SHF (Super High Frequencies) in the GHz range where dish antenna can be used effectively and those freq. won't be traveling 1500 miles. Let us know what you are doing for antennas and bands of choice.
,..........The antennas are both Maco 104c tuned for 10 meters. If beamwidth is @ 65 degrees, I will not have to make any adjustments. Nevertheless, I am still puzzled about the effect of declination when the antennas are set solely through a magnetic compass (wheather coordinates are obtained by tracing a line on Google or using old Cartesian maps). One interesting detail is that the azimuth provided by Google from point B to A is not simply a 180 degree reversal of the azimuth from A to B (it differs by several degrees). It is for this reason that I wonder if Google readings take in consideration any declination. Thanks a million for your inputs.
The difference is due to the curvature of the earth not declination. When I beam to East Africa I beam due east at 90 degrees while the return path is at 312 degrees not 270. Only if the antennas are pointed due north or due south is the return path exactly 180 degrees different.Set the antennas up as close as you can and do not worry about it. 65 degrees means the antenna has to be off by 33 degrees in order to drop the signal half an S-unit.
Google Earth
Another neat thing you can do is right click on your path and choose "show elevation profile".
Another neat thing you can do is right click on your path and choose "show elevation profile".