Antenna Height Question


#1

Hello all,

I have a question regarding antenna height.

Currently I running the Flightware 26 inch antenna up on the roof.

It’s on a 10 foot mast. It’s another 15 feet if you add in the height of the house.

The house is at 39 feet above sea level.

I am running the flightware pro + fed by 50 feet of LMR 400.

I believe my range is mostly limited by the geography. I can receive pretty well out to 200 miles.

I’ve been curious if adding another 10 feet to the mast would make much difference?

Or would it be better to shorten the run of cable between the antenna and receiver?

Right now I have the gain set to auto (-10). Is there anything to be gained by adjusting that manually?

I don’t know if there’s a lot that can be done. I am in the San Francisco Bay Area and I think the geography (lots of hills and mountains in the distance) probably plays a large role in reception of long range planes.

Mostly just curious if I can optimize things.

Thanks!


#2

This website gives your cable loss as 2.4dB, which I think is not so high.
Surely getting your antenna higher up and shortening the cable, will give you some range gain, but I am not sure if it is worth the effort.


#3

I assume you are also using the FlightAware 1090 MHz Mode S filter in your setup. If not, I would do so unless you live in a rural area.

Before going to all the trouble of raising your mast, try experimenting with some manual gain settings. There are some good threads on this sight to explain how to obtain optimum gain for your particular application. My gain is currently set at 36.4 but I have a lot more experimenting to do. With the holidays, the air traffic in the greater Miami area has been a little erratic, so I’ve put off making any further adjustments until the airline schedules have gotten back to some semblance of normal.

My mast height to the base of the my FA 26" antenna is 24’ AGL giving me 33’ AMSL. I’m also using LMR 400 but only about 30’ because I’m trying to keep my cable length as short as possible. I’ve been averaging about 160 position reports beyond 200 nm for the previous 24 hr period. ie “Positions Reported by Distance from Receiver”

That all said, if it’s not that difficult for you to raise your mast, definitely go ahead and do it. I think you will be pleased with your results. Mast height, is a BIG factor in receiving ADS-B signals at greater distances.


#4

It is worth increasing height of antenna to bring it above the surrounding obstructions (tall trees, tall houses etc), so that it can “see” the horizon in all or most directions.

Any increase of antenna height beyond this point is very little gain with un-proportionately high cost & effort.

Please first check maximum achievable range for YOUR LOCATION and ANTENNA HEIGHT by the method given in first post of this thread. If you have already achieved it, it is unlikely that you will get any further increase in range by increasing the antenna height.

What is the Maximum Range I can Get?

THEORETICAL BACKGROUND
Overall Range = Contribution of Receiving Antenna Height to Range + Contribution of Transmitting Antenna Height to Range
= 1.41 x √h1 + 1.41 x √h2 miles,
where
h1 = height of Receiving antenna in feet.
h2 = height of Transmitting antenna in feet.

For plane height 45,000 feet, transmitting antenna height = plane height = 45,000 feet:
Contribution of Transmitting Antenna Height to Range = 1.41 x √45000 miles = 299 miles

CASE A - Receiving antenna height = Mast 10’ Above House + House 15’ Above Ground + Ground 39’ AMSL = 64’ AMSL
Contribution of Receiving Antenna Height to Range = 1.41 x √64 miles = 11.3 miles

CASE B - If Receiving antenna height is increased by 10’, it will be 64’ AMSL+10’=74’ AMSL
Contribution of Receiving Antenna Height to Range = 1.41 x √74 miles = 12.1 miles

Increase in range by increasing antenna height = 12.1 - 11.3 = 0.8 miles

Note: Above calculations assume a level terrain without obstructions such as hills, tall trees, tall houses etc.
If the antenna location has above noted obstructions, the range increases considerably when antenna is raised, till it is higher than these obstructions. once at this height, any further increase in height results in little gain at considerable cost & effort.


#5

if it possible to shorten the cable do so, it is a quality cable so leaving it wont be the end of the world.

Playing with the gain is worth a go depending on where most of your aircraft ranges are.

The reasoning is this, the default gain setting is -10 (which is automatic, i’ll assume FA’s dump1090 does the same as the old dump1090) which in most cases is absolutely fine. The problem with it is its meant for continuous signals (like tv) so the short bursts of ADS-B are ignored, so it tends to ramp up to maximum.

If your aircraft are mostly at maximum range then this is fine as will go to maximum gain. However if your aircraft are mostly close by the ADS-B signals will saturate the receiver and be missed so lowering your gain will increase the message rate and possibly aircraft.

Its all a bit of a trade off and some people notice no difference at all.

If geography is is the limiting factor in your range adding height wont help but if you have the bits or it isn’t going to cost you much why not try it anyway.


#6

OK, so did some math and looked at “heywhatsthat.com” and I’m pretty much getting exactly what is being predicted. I might be doing a little better than what the website predicts but overall it’s very close.

I don’t think adding height is going to get me much. Seems geography is the limiting factor.

I might play with gain settings just to see what that does.

Thanks for the replies!


#7

There’s really no reason to get a long range. The advantage of flightaware is that there are multiple receiver sites.

If all you get is 50 miles, and have a low garble rate, then that is better than 200 miles with a high garble rate.


#8

How do I check my “garble rate”? I’ve not heard this term before.

FlightAware kind of encourages users to capture as much data as possible by ranking us against each other.

My reasons are more personal. I think it’s interesting to see what is flying around up there. I also enjoy the radio aspect and like the exercise of improving my reception.

There are so many receivers in my area I don’t think I’m really adding much to the FlightAware universe.


#9

Question, what would be the ideal height for the antenna? Right now I have it approx.30FT but planning on increasing coax tomorrow and raising it up higher. Also, I am a Ham Radio operator and this 1090MHz ADS-B Antenna that I am using is strictly receive correct? Only ask because I have seen people using yagi’s for the antenna. Wouldn’t it be better to have an omni-directional antenna if its receive only?


#10

Hi,
It hardly matters after 25ft…cause as per the maths,after 25ft as antenna height, your maximum range for airplanes at 33000,34000,35000 ft will be 423.565,429.760,435.870 km respectively.For 50ft antenna to detect an aircraft at 30000ft height the maximum range will be 409.1km but for 25ft antenna for same aircraft the range is 404.4km,Not so much difference right? You can get more height to have an obstacle free horizon but if you have that already 30ft is well enough if you are not in city.Make sure to set the correct gain for the receiver. It matters a lot.

Regards,
Arush


#11

Well thanks so very much for the reply. I am going to raise it only because it’s over-all in a very bad location. Moving it and raising it will be rise in the long run. As far as the gain how would one set the gain on the receiver? Using a USB flightaware and don’t remember having the ability of really setting anything on it. Pretty much plug and play in my raspberry pi.


#12

Hi,
I am using an orange,so gain setting is easy for me.there is a touch screen in it. But if you want to set gain there is a lot of discussion…just search gain. Having correct gain means you have optimized no.of aircraft detected,position and coverage altogether.I guess it’s pre-set in your fa dongle.


#13

I was looking for the orange but couldn’t find it. Only site is FlightAware for the orange or are their others? Amazon no, EBay no.


#14

www.rtl-sdr.com sells a dongle that is almost identical to the FA orange dongle.

Also, you might try NooElec:


#15

“Orange” in this context is a FlightFeeder Orange, which is a FA-managed device that has a touchscreen interface for configuring some things. They are not available for purchase.

For any sort of rtlsdr dongle with a PiAware sdcard image, you can configure gain by running piaware-config rtlsdr-gain


#16

YES and NO.

YES if your antena’s view to horizon is blocked by surrounding tall trees and buildings etc. Raise it slightly above the height of these obstructions and you gain a lot in terms of maximum range. Please see SKETCH-1 below.

NO if your antenna is already above surrounding obstructions such as trees and buildings. Please see SKETCH-2 and TABLE-1 below.

SKETCH-1


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.

SKETCH-2


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TABLE-1
Assuming no obstruction to view horizon in all following cases:
Case 1: Antenna at 25 ft above ground, max range = 306 miles
Case 2: Antenna at 35 ft above ground, max range = 307 miles
Case 3: Antenna at 50 ft above ground, max range = 309 miles