Inspired by @SoNic67 antenna in a tree I set out to test out a similar setup here in my tree-filled location. Usual FA antenna, RTL-SDR 1090 LNA in a H2O proof box. I looped a line over a tree branch 50 feet up to which a nice small sailboat pulley block is attached. A line is then run through the pulley to hoist the antenna much like a halyard raises a sail. I lucked into a huge spool of RG6 at a consignment store but still sought as short a run as possible for the height.
That short paragraph really took a fair number of hours over several days to accomplish, due to a most uncooperative tree and high propensity for klutziness and ill advised iterative design on my part.
General notes: I added a strain relief mechanism consisting of a 7 inch plastic wheel ( from a gas bbq grill or something) with the coax looped around that to attempt to gracefully allow the coax to exit the scene. Not perfect, as they say, it was all I had at the time. It loosely complies with the spirit of the bend radius specs of the cable. Although this is a temporary install I sealed and taped each connection with self amalgamating tape and regular tape on top of that. I ended up with a 95 foot run to the receiver.
Results are not what I expected but that’s why we experiment I guess.
NM Range. After a serious amount of scheming to understand exactly how much a higher AGL antenna would help, both using the Hey Whats That and using some of the less obvious features of of Google Earth I figured that about 50 feet above ground level was going to increase the radio horizon for ADSb above that of my other test antennas.
Imagine my surprise then when a 20 feet higher LNA amped antenna results in no appreciable increase in range. Bias-T milliamps correct, Clean noise scans. Gain tweaks. Sacrificed a bottle of wine. No joy. It’s a puzzlement, although I am still working the problem.
My mate recently put his FA antenna on the roof with a Uputronics preamp <1m away powered by bias-tee from the RPi in the attic. Prior to that the entire setup was in the attic with the Uputronics powered by USB from the RPi.
We similarly anticipated a decent increase in range. What happened instead was:
The range coverage became a bit more circular, with previously attenuated directions now showing activity much further out. This was as a result of the antenna having fewer obstructions and being a few metres higher up.
The parts of the range which were already quite good did expand a bit, around 20 NM in places.
More messages were received 24/7 and they were stronger.
More aircraft were seen within the slightly modified range, and they included aircraft on the ground, ground stations and previously difficult to reach aircraft near the edge of the range.
It’s not too far off the horizon in a few directions but there is definitely still some extra range to be had by getting the antenna a bit hgher again at some future date. It looks like height is indeed king when it comes to range, and as you get higher the range firms up, becomes more circular and you get more interesting things going on in it.
We’re now playing with changing gain at set times throughout the week to see if this can extract a bit more from the setup.
Well, congrats for experimenting. I have really tall trees around, so that was my intention, to go past most of them. Makes no sense to try to get much higher than that, the planes are at 40,000 ft up, we can’t get even 1/100 that high!
My experience:
I did attach the cord on middle of the PVC conduit, not from the top.
In that way, pulling the cable connection point up at the branch level, “pushes” the antenna higher than that branch.
Also, on the bottom part, I had left attached a string that I have then pulled tight, to keep the antenna more vertical and not moving in wind.
In my case the “Case 1” example is partly true with a less of an effective angle once all the factors come into play-
What we see as a horizon plot when running “Hey Whats That” is largely terrain-based, without regard to houses or trees. I am not attaining the range HWT depicts, by a significant margin.
Using the Google Earth line method I posted here https://discussions.flightaware.com/t/google-earth-line-of-sight-how-to/60068 where the imagery supports it shows actual trees and houses and whatnot that are in the way on a certain vector- and how far away they are. ( closer objects naturally mask a wider arc )
Considering Line of Sight as purely a high school geometry problem shows a lack of RF understanding.
Allowing for the Fresnel zone will give you a different max range depend how far an obstruction is from the receiver.
@geckoVN, there are a lot of people who are much more knowledgeable than I about RF and I’d be the first to admit I’m frequently learning as I go. If I’m lucky…sometimes it just bounces off meand I ask if anyone needs more ice and head for the kitchen…
So in the example of an ADS-B plane to ground scenario, with the transmitter constantly in motion in all axes, is there some way to model this ?
If I understand what I’ve read, a tall object at the midpoint of the ellipsoid might obstruct signal more than the same height object closer to the endpoints where the radius of 1st zone fresnel is smaller ?
Yes - exactly!
For ADS-B, this only matters as an aircraft approaches the horizon/max range.
On a static point-to-poiint link, moving the antennas a few meters may change the performance significantly.
With a moving target like a plane, there is not much you can do (other than get your own antenna higher), but may go a long way to explaining why predicted range is not achieved.
Unfortunately many of the offending conifers are on other peoples property. Some are impressively tall and they mock my puny RF games. I call them The Block Forest.
I know how you feel. My neighbor has a tree that dwarfs mine. Is an oak and now, in winter, it’s OK, but when is full of leafs is significantly affects reception in that direction. A little further is a full line of those trees, because it’s a creek there so no hosing development. Again, much better reception now in Winter.
And yes, the leafs are are only attenuating the signal, not straight-up killing it. So a receiver with better signal dynamic range helped me.
That’s why this hobby is so much fun for me. Challenges
PS: My son is renting an apartment at 15th floor of a building (180 ft above ground?). Has not too many obstructions (some other buildings), from his window, with a FA blue stick and a tiny antenna, gets planes from 270 miles away. Only in an 90-100 degree sector that is. Oh, well…
