Really didn’t want to do a post like this, but… Let me preface this by saying I’ve spent the last several days plowing through message boards, guides, and videos, which unfortunately resulted in getting me a bit more confused as I went along.
Basic Scenario:
For the most part, I’m attempting to set up a feeder for FA and FR24. As a heavy business traveler, I like the idea of getting the greater account access, and as a semi-hobbyist (when time allows) I’m also interested in the tracking and such I can do on my own. To that end, I’m trying to build a feeder that has a little bit of future proofing in it. Will likely just start with 1090, but interested in being able to add 987 without having to rebuild the world. Current plan is to use the ADS-B Feeder Image I found in a thread here, with a prefab rpi4 kit (case, fan, power supply, etc…) and whatever antenna/sdr dongle seems to be the best recommendations these days. I’m hoping to consolidate as much of it as I can to Amazon as I have some gift cards piled up on there I’d like to use.
Actual Questions:
So the first question was would an 8gb pi make a difference trying to do both 1090 and 987 or is 4gb plenty?
Next up, I see references to antenna that can do both frequencies, but am I correct in assuming no matter what I’d need 2 independent dongles, or can a single sdr parse both using the processing power of the current rpi boards?
Finally, is there an updated guide around that reflects the current hardware options?
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The RPi 4 is a great place to start and will give you plenty of room to grow with nice physical connectivity right from the git go. I have the 8 gig and it is way over kill because I am in a heavily trafficked 1090 environment and the system uses under 1 gig consistently. 4 gig of mem is surely a happy medium.
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Welcome to the forums @Moebius01, you’ll find plenty of help and advice here.
Just to back up what @CraigWoodThomas said about 8GB probably being overkill, I’m currently running a Pi3B with 1GB and a Zero 2W with only 512MB, both are currently using <150MB of ram. I’m in a generally low activity area in the UK though and both are 1090 only.
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The more I’m reading, definitely agree on the ram. Next up I’m trying to learn on the whole antenna/dongle thing if I want to add 987.
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Even a Pi3B or B+ can handle two dongle receivers to cover 1090 and 978. Be sure to have a good reliable Power supply capable of 2.5 amps, since your USB power drain will be a bit higher than usual. The Pi4 will easily support both dongles and have CPU power to spare.
If your 1090 receiver is an Airspy Mini or R2, the suggestions change a bit. Airspy receivers provide 12 MHz or 20 MHz sampling speeds vs the regular 2.4 MHz sampling speeds of most low cost receiver dongles. Airspy’s also use a more intensive processing software, (airspy_adsb). Airspy’s improve your numbers by 1 - 8 %, and may not be worth the extra planes at distances. Add in the associated Low Noise Amplifier, assorted connectors at around $150, and may not be worth the extra cost. And airspy’s are heavy users of the USB bandwidth, thus affecting the utility of a 978 MHz dongle on a Pi4. The extra memory of the 8Gb model will not help.
Onto antennas for dual frequencies. You would need a signal splitter, not just a T connector. Preferably a splitter that sends the two frequencies to separate output connectors. Cables from there then go to the respective dongle receivers. It is much simpler to use separated antennas for each receiver, spaced apart (with the 1090 higher or equal height). Probably more reliable also. Just a thought.
Dongle receivers are single frequency devices only. For example, the blue FA receiver for 1090, and a yellow FA receiver for 978. The FA receivers are excellent, though other receivers may be better or worse, I have no experience with other ones.
Not sure about any updated guides, Others here may have better information on those and the topics above as we all have different experiences in this. Best wishes and have fun tricking out your new systems.
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Well done, Astro. You have provided some very nice detail there that we can all benefit from. Always learning here! Bravo!
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My understanding is that signal splitters divide antenna gain by the number of outputs - so splitting to two receivers would only supply 50% of antenna signal to each. That would mean that you would need an amplifier before each receiver, but when you do that you are also amplifying any noise that was introduced by the additional connections and by the splitter itself.
I think that in most cases, trying to save money by using a single antenna and a splitter ends up being a false economy in that you will likely spend more than the cost of the second antenna to try to get usable output. Second issue would be that an antenna that is trying to be suitable for both 1090 and 978 is likely to become an example of “jack of all trades, master of none”.
edit to add: I would focus on getting a good 1090 setup to start. Get it tuned and providing the information that you need.
978 is interesting, but in my setup, where I am between PDX and SEA, I get a ton of west coast US commercial traffic, plus flights to and from Asia to SFO, LAX, SLC & DFW. In all, anywhere from 900-1800 flights per day, depending on time of year and weather. I am also within 10 miles of at least 5 general aviation airfields. My 978 system picks up 5% or less of the number of planes - anywhere from zero to maybe 120 in a day. I am grateful to FlightAware for providing a FlightFeeder for that purpose, but I don’t think I would be happy with the value if I had paid out of pocket for an antenna, cable, filter, amplifier, and dongle - well over $100.
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Wow - you are way ahead on the learning curve than most beginners. Basically yes, but a single amp before the splitter helps.
A diplexer rather than a splitter would be better if anyone made one, but AFAIK there isn’t one on the market.
As for “is 8gig better”, a 32bit OS can only address 4gig, so no, 8gig won’t help and as for “future proofing” with computer gear - that’s a lost cause.
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Future proofing in this case is more just making sure I can handle both 1090 and 978 if I decide to add it in the future. At first I wasn’t sure if more memory would help on that front, but from more reading definitely seems not to be the case.
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Is anyone familiar with any of the starter kit providers on Amazon? The all look about the same with the exception of the kit from GeeekPi seems to have a 3.6a power supply where all the others show as 3a. Normally, I’d be sourcing the pieces myself, but for the purposes of this exercise, figure a kit gives me most of the stuff to start.
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My only experience is with the CanaKit packages. I bought this one almost 5 years ago:
https://www.amazon.com/CanaKit-Raspberry-Premium-Clear-Supply/dp/B07BC7BMHY
I threw away the cover for the case because it seemed to run hot.
I started out with one of those little mag-mount antennas that sell for about 5 bucks and the FlightAware Pro Stick (blue) dongle, then upgraded to the Official FA 1090 (26 inch) antenna, then added the FlightAware light blue filter. I moved the antenna from dangling inside an upstairs window to a an unused Dish Network satellite dish mount on the roof, with 15 meters of decent-ish cable, and finally added a cheapo Chinese LNA to help make up for the cable loss.
In 5 years the only failure I have had was an SD card that started acting a little wonky. I was able to clone it to a new one though, and that one has been running for more than 2 years.
So, yeah. The kits are probably fine. Just make sure that the “extra” stuff they include adds to the value, and not just to the price.
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Just for your planning purposes, I replaced a RPi Zero 2W last week with a RPi-4B/2g for $53.21 shipped and a case with fan, & 3a power supply for $19.64. $72.85 total.
Both came from the E place.
Jay
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978 MHz addition would only make sense if you are located in the USA, if you are in Europe it won’t be much use. 
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Good point Tom. @Moebius01 where are you located?
It might it easier to suggest sources for various bits of kit.
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Located near KMEM. That’s where the hobbyist part of me kicks in. Would like to try to set up a few timelapse recordings of the FedEx overnight banks. Probably less need for 987 in the area, but will depend on how much it picks up.
I’m trying to source as much from the big A company as I can because I’ve got a bunch of gift cards stored up on there, so any tips on SDRs and Antennas that can be found there would be greatly appreciated. I do see a Radarbox green combo that has dongle and a 66cm antenna and cable. Haven’t found too many reviews or posts on Radarbox one way or the other. More of the “it works” kind of stuff. 
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That’d be it. (We’re on the Flightaware message boards, I figured people would think in airport codes. 
)
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I’ve never had cause to fly to Memphis, so I had no idea what that code was. Thought it might save some folks having to look it up. This forum is worldwide, so there’s no telling.
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I know my airport codes 
both domestic and foreign 
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Tom, you might want to have that looked at. Ha Ha!
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