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.

There is special (usual means expensive) combiner/splitter equipment available if two antennas have to be combined.

Can you give more information about this one?

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:

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.

[abcd567]

The splitters commonly available for Dish/TV have insertion loss of 4 dB to 8 dB.
This is OK for Dish as the dish has a LNB mounted at dish, and the LNB has a built-in Amplifier.
For ADSB this much attenuation is killing, unless an amplifier is installed. Some hobbyists have successfully used low cost satellite in-line amplifier for L Band (950 MHz to 2050 MHz) for ADS-B 1090 MHz.

3 dB attenuation = power reduced to 1/2 
6 dB attenuation = power reduced to 1/4
9 dB attenuation = power reduced to 1/8

The isolation between two inputs (2 antennas in this case) of these TV/Dish splitters is generally of the order of -25 dB to -40 dB, which is OK.

[Boudewijn]

ok abcd567,

Thanks for the additional info. I take it into my considerations. The biggest problem is that if I place a second antenna these should'nt overlap each other's field of view.