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.
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)
The formats should be compatible in both directions, in theory; dump978-fa includes some extra metadata, but the message format was already set up to allow that. The main thing that would need work if you wanted to use the legacy dump978 would be working out how to get the data onto a listening TCP port. But there’s no real reason to use the old code; AFAIK everything that you can do with the old dump978 you can also do with dump978-fa, and with a lot less shellscript glue.
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I have a site that will be a pita to add a second antenna. I have been doing some testing from home using dual antennas and have the software setup how I like it.
I have some questions on merging the two RF paths to use a single antenna.
Currently, for 1090 I have:
FA 1090 antenna → RTL-SDR Blog Tripple filters amp → FA Pro Stick Plus
And for 978 I have:
FA 978 antenna → FA Dual Band filter → RTL-SDR Blog Wideband LNA → NESDR SMArTee v2.
These seem to be working okay, but now I’d like to switch to one of the dual band antennas from ADSB Exchange and combine the RF path from the antenan to the RPi’s enclosure.
I think I can do that by using the ADSB Ex antenna, and the filter/LNA setup from my 978 setup now. That should filter out most of the junk and only feed 978/1090 into the LNA.
Once in the box, I am less sure what to use. I know I need to split the RF path, preferably filter each, and have a bias tee to feed power to the LNA. I don’t mind spending some money if it improves the setup.
My thought is to use the FA Pro Stick Plus (blue) for 1090 and either the NESDR SMArTee v2 if I can use it’s built in bias tee, or the FA Pro Stick (orange) for 978. I found this Stratux 1090 MHz + 978 MHz splitter, but can’t figure out if it will pass power from the output side to the antenna. I’m also not sure how much isolation it will have, and the only current review is not glowing.
Any thoughts on direction for this? Is there a microcircuits splitter that will pass power I should be looking at?
You can find an appropriate model that will pass DC from one side.
I’d probably use the smartee with the rtl sdr triple filtered LNA for 1090 MHz.
Get a microcircuits splitter with some separation.
Then a bias-t to feed the wideband LNA with power, placed between the splitter and the wideband LNA.
If you want to max out the system, i’d probably use the uputronics 978 MHz filtered LNA together with a non-amplified dongle, but i suppose the pro stick would work as well, might be too much gain though with the wideband LNA as well.
You might even want to get a 5 dB attenuator and place that before the splitter so you don’t have as strong a signal for the following LNAs.
I suppose if you use the uputronics 978 LNA and rlt-sdr 1090 LNA after the splitter, separation wouldn’t be that important and you could just use one of the cheap Y cables to split?
With the wideband LNA you could also get two 5 dB attenuators and place them behind the Y which would also give you some separation.
That might be the best bang for the buck! 
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