AirNav RadarBox and RadarBox24.com > AirNav RadarBox and RadarBox24.com Discussion
EXTRA ANTENNA
Boudewijn:
Is it possible to add a second antenna to my RadarBox pro 3D?
This is because it's 'blind' to the South-East.
So, I want to place a second antenna at my balcony wich is located on the South-East side of my apartment.
I bought a splitter by Ali, but when I use this then the ammount of flights drops dramatically.
neroon79:
Hello Boudewijn,
what kind of splitter have you bought? If you have bought one for Cable, Sat, Terestrial TV and Radio it won't work due to an impedance mismatch between the splitter and the ADS-B antenna / antenna cable. TV cable etc. using 75Ohm impedance, ADS-B antenna cable has an impedance of 50Ohm. If you connect equipment with 50Ohm impedance to equipment with 75Ohm impendace you get reflections and therefore signal loss at the interface point.
As ADS-B signals do not have a high signal strenght the insertion loss of the splitter is critical too.
Furthermore you don't want to split signals but you want to combine signals. There is special (usual means expensive) combiner/splitter equipment available if two antennas have to be combined.
Next general problem:
The signal propagation time in the cable. If you are using two undirected antennas with partly overlapping reception ranges the following will happen
if the connecting cables don't have exactly the same length:
It is possible, that due to the difference in the signal propagation time the same data packet reaches the receiver (splitter/combiner) with a slight difference in time. In that case the two received packets can interfere in a way that they get unreadable or delivering false data. The difference in length must be at least 10 times smaller than the lenght of one symbol of a received data packet travels in the cable during the time that symbol lasts.
Ingo
Boudewijn:
Hi Ingo,
Tnx for your reaction.
The splitter is 50 Ohm. Sometimes you can use a splitter the other way around, i.e. SP3 from RF systems. So, my idea to use it conversely as a combiner.
--- Quote ---There is special (usual means expensive) combiner/splitter equipment available if two antennas have to be combined.
--- End quote ---
Can you give more information about this one?
--- Quote ---The signal propagation time in the cable. If you are using two undirected antennas with partly overlapping reception ranges the following will happen
if the connecting cables don't have exactly the same length:
--- End quote ---
Actually, you're saying it is impossible?
tnx Boudewijn
neroon79:
Hi Boudewiojn,
If you disconnect one of the antennas from the splitter, does the amount of flights increase again? If not the purchased splitter can't be used as a combiner.
I needed supply several Receivers by one antenna, so I used the following 6-way splitter/combiner (https://www.minicircuits.com/WebStore/dashboard.html?model=ZB6PD-2-S%2B) without any significant loss in terms of reception range and aircraft count. Compared with all previously used setups, including a setup with several BNC Ts that were laying around, the splitter/combiner is delivering the best results. For two antennas / devices that one https://www.minicircuits.com/WebStore/dashboard.html?model=ZAPD-20-N%2B might be a possible solution.
Impossible in terms of absolutely totally without any exception impossible: No, under the following cirmcumstances it should work:
Wavelength based maximum difference in cable length:
Frequency: 1090MHz 1090000000Hz (1/sec)
propagation speed in cable: 210000000m/s (varies from 65% to 86% of speed of light in vacuum, HQ Coax typical 0,84...0,86, RG58: 0,66)
Wavelenght: Lambda= Speed/frequency = 210000000m/s / 1090000000 1/s = 0,193m =ca. 0,20m
security factor: 1/3 to 1/10 --> length difference should be something less than 6cm and more than 2cm.
Some experimenting might be necessarry.
Two antennas with hemispheric reception characteristics looking in opposite directions.
Regards Ingo
Boudewijn:
GM Ingo,
Thanks for the information!
So, I tested the splitter the other way around:
* without splitter > 256 flights
* with splitter and 2 antennas > 67 flights
* with splitter and 1 antenna > 68 flight
conclusion: the splitter is not suitable to use it the other way around
Again thanks for the information and the links. I'm going to take a good look at it and then make my decision.
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