FlightAware Discussions

1090MHz Antenna

Even with a VNA (antenna analyzer), getting some of the more intricate designs of antenna to work correctly is very tricky. Much the same as 23cm (1296 Mhz) signals, 1090 Mhz is also affected significantly by nearby trees and other vegetation.

@MUVR2007
@belzybob
@LFBDBORDEAUX

For each location, the maximum achieveable range depends mainly on terrain around the location. Anyone can very easily determin this for his location by method described in the FIRST POST of this thread

What is the Maximum Range I can Get?

Once you know what maximum you can get, you can compare it with what you actually got. If there is big difference, then it may be because of:

  1. Your antenna is surrounded by tall obstructions such as tall trees and/or buildings. Raising antenna above the height of these obstructions so that it can “see” the horizon will improve range.
    https://discussions.flightaware.com/t/antenna-height-increased-but-range-doesnt/31491/4

  2. If your antenna is above the height of obstructions and can “see” horizon, and you still have a range less than maximum possible, then you need a better antenna. Adding an amplifier may help.

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May I respectfully suggest you look at the Philantenna

https://www.lowflyingwales.co.uk/store/product/internal-ads-b-antenna/

In my humble opinion this out performs the FA antenna - but of course this is location dependent. It’s not expensive either!

Kind Regards

Hugh

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G’day MUVR2007 ,

I built my own 8 element co-linear antenna out of quad shielded 75ohm RG6 cable and have had great results considering my location. I’m only 25 metres or so above sea level but the ranges I receive signal from aren’t too bad. have a look at my VRS range maps here. The spikey one is beast mode and the other is from the base station format (more reliable). The range rings are set at 100km (60Miles or 53NM).

I also modified an old 23 element TV yagi antenna to suit 1090Mhz and aimed it to my Sth West to get a bit more range with another receiver. Its range map is still fairly young but filling out quite nicely too.

All the best,

Goldy

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@Goldy714

Performance of an antenna is dependent on not only antenna itself, but also on antenna location, antenna height, length & type of coax connecting it to receiver. Same antenna may perform better or worst if these parameters are changed. For this reason it is hard to judge how good or bad an antenna really is, unless its parameters are measure with costly test equipment.

The DIY situation lacks costly test equipment. The alternative left for hobbyist to evaluate an antenna is by COMPARISON with a reference. There are two easy references available for DIY hobbyists:

Comaparison #1: Determine what maximum possible range can be obtained at a particular location and antenna height, using method described in FIRST POST of thread What is the Maximum Range I can Get?. Obtain maximum range curve of your antenna using VRS, and compare the two maximum range curves.

Comparison #2: Make an easy DIY 1/4 wavelength ground plane antenna (Spider), swap the CoCo by Spider, keeping everything else same (i.e. same same location, height, coax to receiver etc.), and compare results.

Hello @abcd567

Ok.

I was just demonstrating to @MUVR2007 what can be done as a DIYer. I’m not sure what you’re trying to convey to me there.

Cheers.

Good results with your CoCo. Difficult antenna to get right. Any photos?

The 23 element Yagi should be a beast of an antenna. Any photos?

I think abcd567 is suggesting that you can check how good your CoCo is by installing a piece of software which will work out your theoretical maximum range. You can then see how efficient your CoCo is.

The 1/4 spider seems to be a “standard” easy to build antenna. If your CoCo outperforms the spider then you have a beauty.

abcd567 will be back to correct me if I’m wrong :wink:

Many thanks for your reply @Goldy714

I went with the FA antenna and will report my results with it. I plan to DIY some antennas including the co-linear ones for comparison purposes.
You should be very proud of your antenna, seems to be performing quite well! Also the idea of tuning a TV yagi is very clever, just needing to clip the elements and reduce element spacing. I’m also planning of adding a yagi antenna for just checking the one direction max distance aircrafts I can get (west means atlantic ocean here) so it will be interesting to know.

@triggers: You are right, thanks for explaining.

As you have many years of experiance in Coco making (since 2013, if I remember correctly), and have already made excellent performing Cocos, your comments on this subject are very valuable for other DIY hobbyists.

I remember that you have made successful Yagis too.

@Goldy714: Your Coco gives good results, congratulations. :+1: . You are one of relatively few Coco makers, who could make a good Coco.

What I said in my previous post was suggesting you to asses if your Coco has already achieved (or almost achieved) the maximum possible, or is there still room for improvement?

It will be helpful for all of us if you post some photos of your Coco and Yagi, as already suggested by @triggers .

@Goldy714

Maximum Possible Range from your Antenna Location is shown by blue curve in map below.

I have used aproximate location, as I dont know your exact latitude & longitude, but it will be more or less same if you use your exact coordinates.

Yellow curve for flights at 10,000 feet.
Blue curve for flights at 40,000 feet.

I have used the method described in the thread:

What is the Maximum Range I can Get?
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Colinear Coax from TV coax is a high probability of getting it wrong.
RG6 varies a lot in velocity factor and odds are it will not be exactly
resonant at 1090 but some other frequency.

If you get known coax, preferably with a high quality shield or,
get 50 Ohm coax which is a better match for the FA USB dongle.

Colinears also become very narrow in bandwidth with an in crease in number
of elements. Once you hit 8 elements they start getting narrow and at
16 elements it becomes so narrow that you have to be dead on frequency for it to
work.

There are plenty of other designs that give a broader band width and, if you use coax,
use a trusted coax that has specs , copper or tinned shield with a known velocity factor
for making accurate calculations.

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Fully agree. RG6 uses Foamed Polyethylene (FPE), whose velocity factor depends on degree of foaming. The degree of foaming is different in different makes/models. As a result the velocity factor varies between 0.8 and 0.85 for different makes/models. Better use coax with Polyethylene (PE) insulation, which has a very consistent velocity factor of 0.66 irrespective of make/model.

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I could not have said it any better. Fully agree.

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Ok, I installed the FA antenna with a PVC mast 3m above the roof.
Using the RTL-SDR Blog R820T2 RTL2832U 1PPM TCXO SMA.

For now I get 390km range (still testing) with the plane at 33000ft.

Unexpectedly, I rose the antenna to 6m above the roof with a spare PVC mast I found nearby.
Now the range is now like 80nm instead of 200nm I had with 3m PVC mast. Very strange indeed since I did not change any variable beside the antenna height (same antenna, same coax, same receiver)…

Thank you for the quick reply.

I’m in a rural area.
Yes I agree with you, maybe overloading due to GSM signals. From 700MHz to 1200MHz frequency sweep the RTL-SDR dongle shows high-amplitude signals on 800-820MHz and 930-960MHz. However it is true also that before raising the antenna that scan I had previously made also showed much activity in that frequency band…
Guess I’ll have to play with gain for now since I don’t have any 1090MHz filter…

Definitely lower the gain.
The more signals arrive to the receiver, the higher is the total level on the 1090 band, and increases the risk of clipping/overloading. One close-by but strong signal can “kill” all the others when is overloading.
Look on your sky map at the levels for the planes that are shown. For example, if they are at -2…-3dB even when they are 20 miles out, that’s way to much gain.

Thanks for the quick reply.
I’m afraid I can’t do that because I’m using the RTL-SDR remotely… However I found the Gain Optimization Script I’ll try to run to have a clear picture of what is happening…

My mast is all metal, approximately 8m.

Typically, I can receive ADS-B positions out to 200nm.

During peak times, my message count is around 1000/sec.

Suggest you recheck all connections and make sure your coax shielding is properly grounded.