Co Phasing Antennas

Another use of directional antennas is a sectorized setup with separate receivers for each antenna, to reduce message collisions / fruit or to allow separate tuning of receiver gain (e.g. turn down the receiver gain for the antenna pointed at the nearby airport). But for that, you don’t actually want to combine the antenna feedlines.

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Your assumptions are a bit restrictive. The antenna may be on a 4 story building increasing the line of sight significantly. Geographically it may be 1000 feet higher than the airport.
Now calculate again.
Maybe there are a few trees in the way and voila you could use even more gain.

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Why are you keeping silent after your opening post?
Tell us why you want to use Yagis. Lot of speculation here because of your silence.

Correct! hoping to eventually stack 4 of them

I like to experiment! With plots on vrs its easy to see changes made to an antenna system and I am looking for the furthest signals not quantity. These Yagis will eventually make there way on to my rotator if they work out ok. Who else on here runs stacked yagis? Not many so maybe I am treading on new ground…


1 - Directional antennas

2 - Directional antenna

3 - yagi - do you have experience with directional antennas?

4 - 1090 Mhz beam antenna

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12 ele yagi - lots of room for improvement!

How do you figure that is room for improvement ? Once you reach the line of sight limit, the Yagi won’t be able to go around the Earth curvature.
I am getting similar distances (200+ miles) with an omni antenna and preamp.

Except for some rare propagation event, the ‘law of diminishing returns’ is in full force in this case.

Yes but we are not detecting signals from the ground at this distance but some 30+ thousand feet so yes curvature of the earth will come in to play but at these heights where is the limit?

Really blake? Line of sight even to a plane 30+ thousand feed is somewhere around 200 nautical miles i believe. That is assuming you are not receiving from Mount Everest :slight_smile:

I get out to 200NM from 70ft AMSL. This is only in the direction that I am not blocked by apartments, ridges or mountains.
I can see QF11 (Qantas 747-400) come in from 200NM miles to the West.

We are really limited by the curvature of the earth. High gain antennas and low noise amps can only help so much.

Please first check maximum achievable range for YOUR LOCATION and YOUR ANTENNA HEIGHT by the method given in first post of this thread:

What is the Maximum Range I can Get?

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,
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.


Increase in max range by raising antenna height


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 in range, with un-proportionately high cost & effort to raise the antenna.



Hi can we have a picture of your yagi please

I purchased 2 Wideband Yagi Antenna YA9W-13 860-960 MHz 13 dBi to play around with, I fully understand they are not centered on the ADS-B frequency, but I wanted to play with them using a 50ohm power divider to combine them. At my location I do not have good omidirectional coverage and wanted to point them into the valley where I have a clear view. They maybe a waste of time but I enjoy experimenting.


Have you tried just using one of them to see if it has any gain at 1090 in the direction it is pointed?


The Yagi you purchased, due to its original operating frequency, may be tuned to ADS-B by trimming the elements.

No I have just now received most of the parts to mount the antennas outdoors



Phase matching does not only depend on the cable length. The placement of antennas can be critical. For the farthest planes (if the antennas are in different directions) then there may be no problem. But what if the planes are in common parts of the beams, or the planes are passing over you? You would get unpredictable blind spots in the coverage pattern.
Empty spots due to phase shifting also occurs when one of the antennas is half a wavelength closer to the plane.

There is another aspect that makes it worth redesigning this otherwise good idea.

  • Assume that the directed antennas do not radiate backwards at all (they do not receive signals). Then we can say that we can expect the original gain of the yagi antennas in the given directions, no more.
  • Instead of using complicated antennas in a group, you can use simple pieces of half-wave dipoles that are placed on top of each other (stacked-phased) - at a distance of 0.8-0.9 wavelengths between the “current maxima” points → then your omnidirectional gain is 9 dBd (> 11 dBi) 2 degrees above the horizon.
    Because an auxiliary mast shall be used for the antennas, the gain in the direction of the main mast will be somewhat smaller.
  • It is easy to build a 2-4 way Wilkinson combiner at home for the antennas. Avoid splitters/combiners made of resistive components only. They are unnecesarily wideband - with high losses.
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Cable length affects the delay too. So they need to be perfectly equal, to keep the signal in phase… mm difference counts.