Single antenna for 2 SDR dongles?

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

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

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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1090/978 Splitter/Filter

I’m using this with 2 FA Pro Orange sticks (with integral LNA but no filter).

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@W6cz

Your post answers the question which was asked in another thread yesterday.

I assume you are using one dongle for 1090 mhz, other for 978 mhz. Am I right?

External filters (SAW) for both 1090 and 978 are provided by this diplexer/splitter. There is no need to use another filter.

Yes, that’s why I’m not using the Pro Stick Plus. I don’t need the filter in the dongle. This is a lot cleaner setup then the 2 RTL-SDR v3 I was using with a RTL-SDR ADSB LNA/filter - so I was getting double dinged by the filters in both the splitter and the LNA. I did som calculations using heywhatsthat.com and appear to be getting the theoretical range I should on 1090 and close to that on 978 (not nearly the number of targets so harder to evaluate.

I’m finding a surprising number of small jets and turboprops broadcasting both systems.

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@W6cz

Day before yestrrday I landed to this diplixer on amazon, and it looked very promising so I decided to ask if any one is using it, but I chose wrong thread :slight_smile:

The ProStickPlus has the filter directly after the LNA in the signal path.

It is beneficial for receiving 1090 MHz if only to suppress noise coming from the LNA.
It does not reduce your SNR, rather probably improves it.

Getting rid of attenuation before the LNA is much more important.
But not overloading the LNA with mobile signals is also important, which i’m sure this diplexer takes care of.

6 dB is still a rather big hit to take, when you could have only 2 dB attenuation with just a SAW filter in front of the LNA.
If that reduced performance is worth receiving UAT, then the diplexer works for you.

If you really have to work with a single antenna plus diplexer, i could imagine using a rtl-sdr blog (or other brand) wideband amplfiier near the antenna.

Just to reiterate, that’s not really how signal quality works, once you are past the LNA a saw filter most likely improves signal quality because it cleans up the noise from the LNA.

I’m hoping to put a feeder up at a high level commercial site and I’m limited as to the number of antennas so having one dual band 1090/978 antenna and feed line helps.

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Which dual band antenna you are using?

By double dinged I was talking about the attenuation of the filter in the splitter plus the attenuation of the filter in the LNA.

One from ADSB Exchange.

Yeah i fully understand what you’re saying.

The attenuation after the LNA does not reduce signal quality.
(not talking more than 6 dB of attenuation here, but rather 2 dB from the SAW filter)

Let’s compare with an audio amplifier: Even with no input your stereo when turned up to 3/4 volume produces a certain amount of white noise.
Now you feed the stereo with a weak audio signal, but you can clearly hear it above the noise.

If you make the input signal too weak, you can’t hear it over the white noise the stereo itself is producing.
Now this input level threshold for not being able to hear the input via the speakers does not change if you introduce a resistance into the speaker cables, unless you make the resistance very big.

It’s the same with the LNA, attenuating a bit after the signal is already amplified does not reduce the threshold of input into the LNA you can receive.
Hope that makes some sense.

Now the filtering can even be beneficial to get rid of noise coming out of the LNA that’s not on 1090 MHz. It shouldn’t be much anyway because we already filtered, but mobile signals can be quite strong and another stage of filtering in this case has no negative side effects from the attenuation, so you might as well take it.

.
This one?

https://store.adsbexchange.com/products/5-5dbi-1090-978-antenna

Yes. It appears to work fine. I’m consistently seeing aircraft at the edges of the theoretical coverage. It will be connected with about 50’ of LMR600.

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one antenna & two dongles = with a splitter no problem.
Over two years one of my two setups consists as follows:
5/8 GP antenna ==> ZAPD-2DC+ power splitter SMA-Version) ==> FA ProStick (orange)
AND ==> RTL-SDR V3 dongle
or Standard DVB-T Stick (RTL2832)
or AirNav RadarBox FlightStick

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I have used this y cable with success.
https://www.amazon.com/gp/product/B07STYNB6V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

I use the ADSBx 978/1090 antenna then hit that y cable and into one blue FA SDR for 1090 and one orange FA SDR for 978. I set the serial #s to 1090 and 978 respectively with the rtl_eeprom command.

I am still working with the scripts to get a proper feeding of the 978 data to both FA and ADSBx.

FA shouldn’t be an issue with the guides on this forum.
You’ll need dump978-fa to feed FA, the older versions produce an incompatible format i think.

When dump978-fa is running and producing data on 30978, this script will easily feed adsbx:
GitHub - wiedehopf/adsbexchange-978: The ADS-B exchange UAT/978 feed client for use with dump978-fa
(it will just establish a 2nd beast connection in addition to the existing feed if you are already feeding adsbx on 1090)