FlightAware Discussions

Single antenna for 2 SDR dongles?

#1

I plan to run the 1090 and 768 SDR dongles from 1 RaspPi3 and packed in an outdoor weatherproof box - can I use a 1/4 DIY antenna to feed both dongles? I know one of the dongles won’t have the ideal antenna length but if I’m okay with the reduced range, will it work?

I’m guessing there will be too much signal loss going through a splitter but if not, what kind of antenna splitter is recommended?

#2

If it is a DIY 1/4 wavelength, then why not 2 separate antenns? This will simplify install, and give optimum performance. No splitter losses and no mismatched antenna.

#3

Looking at your stats page it appears that other stations nearby are seeing significantly more aircraft and significantly more position reports over much, much longer range.

At present, it appears you have insufficient signal for one system. I would suggest fixing this before contemplating how to feed two systems with one antenna.

S.

#4

You’ll be getting a minimum of 3dB loss.

If you can tolerate that, you’ll need a splitter/combiner with reasonable isolation (a $5 tee splitter is not going to be sufficient). Look for a splitter which actually quotes an isolation figure; anything more than 15dB should be fine. You can often find suitable Minicircuits splitters secondhand (new, they run to $80+)

#5

Thanks for all the quick replies. My current setup is using the included SDR antennas that have been clipped for 1090 / 978 and they are sitting on small food cans (indoors) - I was using this setup to see if I could get the software running. I’m not interested in a pricey splitter so I’ll just drill another hole and add another DIY antenna.

Once I get the outdoor enclosure tested/working, I’ll move it to a small town airport on the Texas coast.

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#6

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The 3 dB is only in case of an exceptionally good splitter. Most common ones have loss between 5 to 8 dB

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#7

That’s why I said “minimum”, you’ll always have at least 3dB loss because you’re splitting the power two ways.

But if you’re getting 8dB (or even 5dB) you have a bad splitter. Here’s a minicircuits splitter that has around 3.9dB total loss @ 1GHz: https://www.minicircuits.com/pdfs/ZAPD-2-252+.pdf

#8

Using a splitter - yes.
As we know, a splitter ‘splits’ the signal and put half on each output port - hence the 3dB attenuation (in a perfect world).
This is fine if you want the same signal to input to two receivers.

In this case the OP wants to run the receivers on different frequencies, so a diplexer would be a better choice than a splitter.

I am of course ignoring the practicality of building it. ‘Normal’ components don’t behave predictably at GHz freqs.

My recommendation would be to use two antennas.

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#9

$80 for a splitter???

They’ve got to be out of their mind!

https://www.minicircuits.com/WebStore/dashboard.html?model=ZAPD-2-252-S%2B

#10

If you look carefully, you may find this logo on it :slight_smile:

#11

check for splitters on ebay, there are lots of minicircuits splitters up there

#12

Why? That’s pretty normal for good quality RF components that have predictable, documented, performance at GHz frequencies. It’s not just a simple tee.

(take a look at the prices for high-power splitters if you want a real shock)

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#13

I may try one of the used mini-circuit splitters ($20 ebay).

#14

Instead of spending $80 to split one antenna to two dongles (1090 & 978), I will rather purchase 2 x Flightaware antennas in this price, one for 1090 other for 978

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