I have mi piaware antenna in my rooftop and I get maximum ranges of about 200nm in certain directions and about 50nm on others.
I’m planning to raise my antena by about 10 ft, and I wonder if it can get any noticeable increase in my range. In fact I don’t thinc 10ft will make any significant difference avoiding my main obstacle, which is an appartment building behind my house but towards the front I have a prrety unobstructed view, so I don´t know if 10 ft can make any diffrence or if it would be best to invest in a higher gain antenna or an amplifier and keep the same height.
Raising the antenna gives the best gains when it will make it higher than any surrounding local obstructions. After that it won’t increase your maximum range all that much. The reason for that is that your antenna height above the ground is still small in comparison to the altitude of the aircraft you are detecting.
Your total range is the sum of the radio horizon of your antenna, and the radio horizon of the aircraft.
For example, if your antenna is at 100 feet above sea level, and the aircraft is at 40000 feet asl, then your radio horizon is 14 miles and the aircraft’s radio horizon is 283 miles giving a total line of sight distance of 297 miles. If you increase your antenna height from 100 feet to 110 feet, your radio horizon increases to 15 miles.
Increasing from 297 to 298 miles is about 0.3% increase in range.
It’s worth adding height to get over obstructions, but it’s not worth adding height past that unless it’s cheap and easy to do.
Antenna height is good for height over obstacles, but you need a lot of additional height to significantly increase your range. While you can “see through” some obstacles (e.g. there is some limited penetration through trees at ADS-B frequencies), mostly solid obstacles such as a building, chimney, or tree trunk will reduce your range in the direction of that obstacle.
In your case:
If that 10 feet will get you over the roof of that nearby apartment building, then it will help tremendously in that direction. It’s sounds like that’s not the case. However, if your antenna is partially blocked by your roof, chimney, or other nearby object, that 10 feet may offer significant range improvement in that direction.
I can tell you that 10 feet won’t make any difference if you are not able to bypass obstacles (trees, buildings).
For testing i had mine 4 meters higher (approx 10-15 feet) and didn’t see a difference in range.
To get a significant range change, it would need to be much higher.
I volunteered at an aero museum years ago and a friend (fellow volunteer) was asking me about the length of sight from the deck of a ship versus an arbitrary “crow’s nest” and I asked him if I could get back to him. From the surface of a relatively flat plane (like the ocean) it’s about three miles line-of-sight.
He’s a NAVY vet and and GE retiree. I used to call him the Steely-eyed Missle Man. The diagram I found (thanks, in part to professor Google) and showed him says essentially the same thing as your diagram.
The taller your antenna, the better “view.”
I can’t find that diagram right now, but I’ll get back to you lol. Height of the antenna, h, and the normal line at o (right angle to the tangent at o) and well … you get a right triangle. Very good math.
