FlightAware Discussions

Co Phasing Antennas

Especially at the frequencies we’re interested in.


Although the cables are the same length, but the “distance” of one or more antennas is different towards the signal source, then phase and delay still needs to be considered as a good practice.
(If delay counts, we can finetune it by moving the active antenna part a bit - instead cutting another cable.)

To me, it’s easier to keep the cables equal and antennas fixed in pre-measured positions, than trying to compensate later by moving antennas unknown distances…
Anyway this is irrelevant here, because the collisions domain will be the same, with phased antennas or just one vertical stick.

The distance is generally not limited by signal level, but by Earth’s curvature.

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When I started this hobby several years ago, this is what happened.
I live in an apartment where installing antenna on roof is not allowed. I can install antenna inside my apartment near any window.

When I installed antenna in North window, the reception of south side became very poor. When I installed antenna in South window, the reception of north side became very poor.

I decided to install two antennas, one in North, other in South window and combined them by different methods like a solid T, combiners/splitters, phasing harness, but all resulted in severe reduction in range and plane count.

Finally I purchased another Pi and another Dongle and setup two independent receivers, one connected to North antenna, other connected to South antenna, feeding two independent stations. Now the range is excellent in both North & South directions.

For local viewing, I combined their data outputs in VRS on my Desktop.

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I think this is because we are so used to think antennas in relation to radio sources are fixed.

A plane moving in the sky will have the signal arriving variable delays on any two different antennas. Phasing of radio signals works when the antennas are directed towards a fixed source, not when the sources are moving all around that phased array.

Directionality is the whole point of a phased array…

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@obj: Will this arrangement affect MLAT?

Merging feed of two RPi. In this example, I will call one North receiver, the other South recriver.

Both Pi have their independent Antenna+Dongle set.
Both Pi have dump1090-fa
Only South Pi has Piaware data feeder installed.

To merge do following steps on receiver on which you have installed Piaware data feeder.

In example case below, the Piaware data feeder is setup on the receiver facing South, so you have to do all this on South receiver. Note that nothing is to be done on North receiver.

(1) Install socat

sudo apt-get install socat

(2) Create a new blank service file for socat-pipe

sudo nano /usr/lib/systemd/system/socat-pipe.service   

(3) Copy-paste following code in the newly created blank file
Replace XXX.XXX.XXX.XXX by other Pi’s Local IP (in this example case North receiver’s Local IP)


# socat-pipe service for systemd
Description=socat-pipe to pull data from another Pi

ExecStart=/usr/bin/socat -u tcp:XXX.XXX.XXX.XXX:30005 tcp:



(4) Save file (Ctrl+O) and Close File (Ctrl+X)

(5) Enable and start socat-pipe service

sudo systemctl enable socat-pipe

sudo systemctl start socat-pipe

(6) Wait for few minutes then check status

journalctl -e -u socat-pipe   

(7) Check this Pi’s Map in browser (South receiver in your case)

(8) Use following commands to start, stop, rerstart and check status of merging through socat-pipe

sudo systemctl start socat-pipe  
sudo systemctl stop socat-pipe  
sudo systemctl restart socat-pipe  
sudo systemctl status socat-pipe  


sudo systemctl stop socat-pipe  
sudo systemctl disable socat-pipe  
sudo rm /usr/lib/systemd/system/socat-pipe.service   

Mlat will not work if you merge data from more than one receiver like this.

Thanks @obj for clarification.
Just now I made a test setup of merging data of two receivers, and start getting this warning. When I stopped merging, the warning stopped.

[abcd@archlinux ~]$ journalctl -b -u piaware

Feb 20 14:28:42 archlinux piaware[312]: mlat-client(422): Out-of-order timestamps: 106

Feb 20 14:30:10 archlinux piaware[312]: mlat-client(422): Warning: the timestamps provided by your receiver do not seem to be self-consistent. This can happ>

Some one is trying to combine 4 vertical dipoles placed in vertical formation like in the diagram, and connect them using combiners and accurate length coax pieces.


Strictly it’s about gain, although directionality is certainly a common application
If you want gain:

Commercial omni antennas are often phased folded dipoles:

Of course if you live beyond the land of mortals, you steer a static array by altering the phasing.

Phasing harnesses are an off-the-shelf item if you are working in the common bands

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