ADS-B Antenna Splitter

[acarslogger]

Hi all,

I've now got an SBS-1 Classic and an SBS-3 so I decided it would be useful if I could run both at the same time using my existing external antenna. To do so I needed a 'splitter' so that my external antenna could feed 2 separate ADS-B receivers. This is my findings using the TMRF-ADSB-Splitter available from Chris at TaylorMadeRF Ltd -- see his video at http://www.youtube.com/watch?v=vfPz8R9vzhQ .
From what everyone says a typical splitter will have a loss of up to 3dB, which is half the signal strength. So what's that mean for the average user; will my reception range be drastically reduced ? Instead of 200nm range will I get 100 nm ? Instead of getting aircraft on finals to Heathrow at 2nm, will I only able to receive them at 4nm ?
For all those techies who love to discuss dB insertion loss and isolation values and have access to signal generators look away now ! This is a laymans non-technical evaluation of my use of the splitter.
The TMRF-ADSB-Splitter is a substantial lump of metalwork with 3 'N' type sockets that can either be 2 antenna inputs to 1 ADS-B receiver, or in my case 1 antenna input and 2 outputs. Chris can supply all the patching leads required to connect the antenna(s) and receiver(s) to the splitter. The ones supplied seemed well made.
I assumed that local aircraft in good signal range wouldn't be affected, so the effect of a splitter would be most visible where you lose contact with an aircraft. In my case these are low flying aircraft as they disappear on the glide path into one of the local airports, or those aircraft at the furthest distance I can receive - 220nm over the North Sea, Netherlands and Belgium.

Local Plots

From my location in North London, I normally receive Heathrow inbound aircraft on the glide slope onto 27L/R until about 2nm. Over a few days I ran my SBS-3 with and without the splitter and I could see no discernible difference between where they disappeared from the Basestation radar screen.
To try and determine if there was any difference, I ran BasestationLogger for 12 hours to capture the output from port 30003. The following day while Heathrow were still on Westerlies I repeated logging with BasestationLogger but with the splitter included.
I then looked at the BasestationLogger outputs and extracted the final position (latitude and longitude) recorded for each aircraft landing at Heathrow. I then calculated the distance to the runway threshold. I discounted the top and bottom 10% to hopefully avoid oddities including those aircraft not sending accurate ADS-B positional data, and then averaged the remainder.
Without the splitter the average distance from the threshold to where I lost the aircraft signal was 1.8nm. With the splitter in place the distance was 1.9nm. A difference of 0.1nm. I repeated a similar test for Stansted where the difference was even less that 0.1nm.

I'm happy that the splitter doesn't significantly affect the reception of local aircraft.

Distant Plots

There is the point where I either first receive or lose contact with plotting aircraft. Looking at the Basestation radar screen I could see no discernible difference with or without the splitter but it's very difficult to consistently see aircraft as they are often given direct routing, are at different flight levels and hence at different positions in the sky so there is no clearly defined points on the radar screen where consistent comparisons could be made.
So I used SBSPlotter, http://jetvision.de/sbs1.shtml , to try and determine if there was any difference. I tried running SBSPlotter for a few hours with and without the splitter but the results were all over the place. To get a more consistent range plot SBSPlotter needs to run for a long time. So I recorded the SBSPlotter output for 24 hours without the splitter, and then 24 hours with the splitter. The outline files generated by SBSPlotter were then displayed on the Basestation radar screen, purple line without and the green line with the splitter.
Even running SBSPlotter for 24 hours there are still peaks and troughs in the range with the occasional plot when using the splitter being greater than without. Not what you would expect. To get an even more accurate plot I think you need to run SBSPlotter for a very long period of time. However it does generally show that with the splitter included there is a slight reduction in range in the order of 10nm at the extreme distant points where the range is greater than 200nm. See attachment.

I'm happy with the splitter. There is a slight difference but not what I call significant, and generally nothing discernible.

Disclaimer - there are other splitters available from other manufacturers whose performance may vary from the TMRF-ADSB-Splitter. This wasn't intended to be a comparison between manufacturers rather than a simple observation of the impact on using a splitter on my Basestation setup.

Regards
Stuart


[Attachment deleted by Admin to save file space]

[junglejet]

I use very simple cheap (about 1 €) 3 way connectors for my Beast/SBS-1 setup.
I cannot see any difference (but I am not that picky).
If things get worth putting a preamp just below the antenna will make the splitter quality not relevant at all.

[Anmer]

When I used a simple, cheap splitter, there was a significant reduction in data being received by one of the receivers.  When I swapped the connections, the otyher receiver suffered the same reduction.

But it's easy and inexpensive to test.

[birdie]

Have anyone here tried out " Space-diversity " antenna system ?

2 Antenna feeding into the receiver ?

[Chris-G0WTZ]

I am just recording plots of two antennas into one SBS for Flat dwellers
Quite good results
Here is the thing for a normal set up

If I had two identical antennas mounted in the clear at about 1 metre apart that would give an increase of 3db and the splitter gives 3db loss so it is of no real use in normal use. (You also end up with odd radiation shapes.
However if you have a flat with a window at the front and one at the back put two window mount antennas into the splitter you seem to get good results
Give me a few days to finish the plots

Regards

[birdie]

I am just recording plots of two antennas into one SBS for Flat dwellers
Quite good results
Here is the thing for a normal set up

If I had two identical antennas mounted in the clear at about 1 metre apart that would give an increase of 3db and the splitter gives 3db loss so it is of no real use in normal use. (You also end up with odd radiation shapes.
However if you have a flat with a window at the front and one at the back put two window mount antennas into the splitter you seem to get good results
Give me a few days to finish the plots

Regards

Hi Chris,

How is the plot going ?