Total ignorance...need help (LNA + Bias tee)

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VonEmber
Posts: 2
Joined: Thu Jul 15, 2021 10:24 am

Total ignorance...need help (LNA + Bias tee)

Post by VonEmber » Sat Jul 17, 2021 11:53 pm

Hi everyone.

I cannot apologize enough in advance for the stupid question I'm about to ask. This ADS-B hobby is a lot of fun but it's absolutely obvious I have much, much to learn.

I have a FlightAware Blue (pro?) stick. I've been reading on many different forums that adding an LNA would improve my coverage (I have my antenna on the roof with 360 degree views). I found the RTL-SDR triple-LNA on Amazon but I noticed it needs to be powered. I have two questions:

1. Is it easier to get the RTL-SDR v3 stick with a bias tee already included?
2. Can I use my blue Flightaware stick with that aforementioned LNA, and use an external bias tee?

If #2 - that's where my ignorance comes in. What...exactly...can power that LNA? Can someone point me to a product or educational link, or just describe what I need to get?

Thanks in advance. Again - apologies for the dumb question.

Stromeko
Posts: 43
Joined: Wed May 01, 2019 6:32 pm

Re: Total ignorance...need help (LNA + Bias tee)

Post by Stromeko » Tue Jul 20, 2021 10:27 am

VonEmber wrote:
Sat Jul 17, 2021 11:53 pm
I have a FlightAware Blue (pro?) stick. I've been reading on many different forums that adding an LNA would improve my coverage (I have my antenna on the roof with 360 degree views).
Assuming you aren't in a very unusual location (i.e. far off any flight corridors or extremely close to an airport or sources of interference like a GSM tower), the antenna location, quality of the antenna and proper adjustment of the gain on the FA stick has a much greater influence than anything you can do by adding an LNA. You should first check what your coverage actually is. and only then try to modify your setup to improve it. Also, resist the urge to modify many things at once. Ideally after each change you record a full week's worth of data to have a good basis for deciding whether it was helping or not.

Coverage isn't a well defined term either, it could mean range (respectively fraction of the theoretical range) or it could mean how many messages that you should have received given the theoretical or empirical range were actually recorded. There are sites that will show you the theoretical maximum range you can "see" given your antenna location and height above ground. Amplification mostly helps with extending the range towards that maximum, but depending on your location you might end up de-sensitizing the receiver (the RTL-SDR has pretty small dynamic range) and then record less messages from near your location. While the volume of airspace in the outer fringes of your range (and thus the potential number of messages) is much larger than nearby, that doesn't translate into more received messages if there's no flight activity there.
I found the RTL-SDR triple-LNA on Amazon but I noticed it needs to be powered. I have two questions:

1. Is it easier to get the RTL-SDR v3 stick with a bias tee already included?
2. Can I use my blue Flightaware stick with that aforementioned LNA, and use an external bias tee?

If #2 - that's where my ignorance comes in. What...exactly...can power that LNA? Can someone point me to a product or educational link, or just describe what I need to get?
I'd personally go with an RTL-SRD v3 plus the filtered LNA and use the built-in bias tee, since you don't need the additional filter in the FA stick if you already use a filtered LNA. You then still have the FA stick to experiment with (with a second antenna). Otherwise you will need an extra bias tee with a DC block to put somewhere between the FA stick and the LNA and feed it 5V from an external supply (old phone charger or similar should work). Of course you need to check that the DC only goes to the LNA and not to the FA stick.

rtlsdrblog
Site Admin
Posts: 2945
Joined: Mon Nov 19, 2012 11:54 pm

Re: Total ignorance...need help (LNA + Bias tee)

Post by rtlsdrblog » Tue Jul 27, 2021 1:45 am

Using the ADSB LNA will improve upon the FlightAware dongle if there is a moderate to long length of feedline between your antenna and receiver.

If you're setup is Antenna -> Long Feedline -> Receiver, then the V3 + LNA will probably work best, assuming you can get the LNA close to the antenna.

Optimal: Antenna -> LNA -> Long Feedline -> RTL-SDR V3 with BiasT

With your FlightAware dongle however, it will work just as well, assuming you can get the dongle close to the antenna too.

Optimal: Antenna -> Short/No Feedline -> FlightAware Dongle

It's best not to combine the FlightAware dongle with an LNA, and the FlightAware dongle already has a front end LNA built into it. So if you add another LNA you can end up with far too much gain. But if you want to experiment, you can purchase external bias tees very cheaply on eBay, Aliexpress etc.

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