FlightAware Discussions

Adding a Low Noise Amplifier to a receiver

I apologize if this has been asked before, but I can’t seem to find any information (Well, I found some, but it’s conflicting)

I’m planning on putting together an ADS-B monitoring station. It will be based on a Raspberry Pi, which is going to be outdoors in an approved weather-resistant box, so it can be as near to the antenna as possible. The antenna will be on a tall pole, so there will still be about 15-20 feet of coax.

My plan is to use the blue dongle to monitor 1090 mhz transmissions. As I understand that should work at least as well as the orange one with the external filter. (Correct me if I am wrong on that. If I’m better off using the external filter, then I’ll do that instead)

I plan on eventually adding 978 mhz monitoring, using the orange dongle, but right now I’m just looking to get going with regular 1090 mhz ADS-B.

The dongle has an integrated amplifier, but I noticed that there are some low noise amplifiers that could potentially be added. Here is one:

I think Nooelec makes one as well.

I want to get the best performance possible, but since the dongle already has an amplifier in it, I don’t want to overdrive it either.

I’m located near the shore in Connecticut, and I’ve played around a bit with an RTL-SDR dongle to see how well I could do receiving ADS-B. My location seems to be a very good one. I have mostly water between myself and New York City, and I’ve been able to pull in flights from North of Cape Cod and inland all the way up to the Quebec area. However, doing so requires a lot of playing around with the gain, and I can’t really consistently get the whole area covered.

So would it be worth investing in an amplifier like the one I linked?

If I did, I’d want to put it as close to the antenna as possible. I could quite easily mount a water tight box right at the antenna.

The filter is good, when it works(I have two). There have been numerous posts of poor quality control.
Test it before you put it up on the mast.
This filter doesn’t suffer from overload like the hab/nevis/uputronics amp/filters(I have many). I have to put cavity filters on the antenna side of mine otherwise they get overloaded.

If you have a lot of variation in signal levels then you may want to also invest in an airspy mini. These have a much larger dynamic range so are able to cope with larger variations in signal level. They do require much more CPU. An RPI 3B or 4 would be recommended.

It is worth it from my experience.
You’ll need an external bias-t: https://www.ebay.com/itm/172460255780
EDIT: don’t use the above bias-t … it lends itself to connecting it the wrong way.
The bias-t you can feed from the 5V RPi board voltage, for example via an old USB cable you cut and connect to the bias-t.

If you use it with the FA prostick+, you will need to reduce the rtl-sdr gain to the 0 to 5 range.

I think it is worth adding a filtered preamp of the sort you describe. You’ve given your goal as “I want to get the best performance possible” which I suspect means you’d like the best from your available range without compromising nearby aircraft to a large degree.

You’ve described a location with a good view. If you have a decent antenna, such as the FlightAware 26" 5.5dBi antenna, and quality coax and a decent receiver, you’ve created the optimum setting for your signal and noise management. Adding the filtered preamp will let you explore those weaker signals, and I suspect you’ll find your nearby signals are not hugely compromised, and you can play with gain and settings to find the balance.

You’re right, you want it next to the antenna before any longer run of coax down. You can power it through the coax using bias tee (the one you linked requires it, and there are others such as Uputronics which support it). If you look at the airspy mini that Jon mentioned, that has a bias tee injector built in which is switchable via software. Or else, for other SDRs, you can buy external bias tee units which connect to a DC supply such as the USB or GPIO pins of the RPi. I’m not that clued up in this area but plenty of others here play with this stuff all the time and have high quality sites set up.

Another option might be to set the site up, maximise the antenna and performance without a filtered preamp, and then add one in the following month with the advantage of now having a baseline from the same setup against which to compare results.

The biast proposed by you does not have any SMA terminal marking, and a user may easily connect the biast the other-way round.

image

I use this one: https://www.ebay.com/itm/132678347178. It is a little costlier, but has the SMA terminals marked RF and DC+RF, and hence has less chance of wrong connection.

image

My second one is this one (sold out) https://www.ebay.com/itm/183768806247

Bias-T

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It’s the one linked on the rtl-sdr LNA page.

If you connect it directly to your USB receiver without an adapter, you shouldn’t be able to connect it the wrong way around.
Or is that the wrong way around, seems that way. :scream:
Wow that would be stupid linking that bias-t on their page …
SO YOU ACTUALLY CONNECT IT THE WRONG WAY BY DEFAULT? …
It seemed like and advantageous product because you don’t need extra adapters.

The comments don’t seem a way to get in touch with them to modify their page, i’ll have to check if they have a mail address or sth. for corrections to their articles.

That is why I purchased the 2nd one, which has the sma male on one end & sma female terminals on the other end, PLUS marking of terminals. Unfortunately it is sold-out

Bias-T

.

In abscence of terminal markings, the capacitor in the SMA’s center stripline is a clue to RF terminal.

Bias-T-3b

Well the markings don’t help if it’s the wrong way around for the particular application and you need adapters anyway.
Really no reason to buy this for the typical usecase of injecting power for an LNA.

Just a random suggestion re. your setup, How about keeping the pi inside but putting the dongle outside on a long usb cable? You can get some long powered usb cables (10 metres÷ in funny units) which, being digital, are pretty much lossless. I’ve done something similar on my setup which means I can keep the pi in the loft where it is easy(ish) to access and has far better WiFi signal that above the roof. Just a thought.

Thanks for all the replies. I am using the Flightaware 1090mhz antenna, and it seems to work very well.

As mentioned earlier with the gain settings: While playing around with the antenna, just using a general purpose RTL-SDR I’ve had good results. Playing with the gain settings can get me some pretty distant aircraft, but higher gain also introduces a lot of noise, so what happens is that while I can get distant aircraft, I also get a lot of dropouts and incomplete data.

Ideally, I just want to be able to leave it on one setting and get optimal results for both local aircraft and more distant ones. Since I’m near the coast, I have good line of sight out pretty far.

So based on what everyone has said, an LNA seems like the way to go.

Anyone have any experience with which LNA might be the best?

RTL-SDR Blog makes one, as does Nooelec and I’ve seen them on ebay from various generic makers. Uptronics makes two, one being the SAW unit and then the considerably more expensive ceramic unit.

I assume the difference is in terms of how well they filter out of band signals.

So with so many choices, I’m just not sure which setup is going to be best.

Right now, I’m leaning toward the RTL-SDR.com preamp, because it’s inexpensive and seems to have good reviews. I’ve always had good experiences with their products.

I was planning on connecting that to the FlightAware Pro Stick Plus ADS-B USB Receiver w/Built-in Filter (the blue dongle)

But then again, maybe I’d be better off getting the orange dongle and the external filter, so that I could put the filter BEFORE the amplifier (Between the antenna and the LNA)

And if i did that… would there be any point in getting the blue filtered dongle? I mean, then I would be filtering it before and after the amplification…

That’s actually the setup I have now, with the RTL SDR. I live in an apartment, so I don’t have direct access to the roof, but I’m on the top floor, so I have an antenna pole that extends beyond the roof line.

My plan is to get the weatherproof box and put most of the system outside. I’ll start off with a 1090mhz system, and then once I’m happy with the way that works, I’m planning on next adding a 978 Mhz UAT receiver.

After that, I’d like to add the capability to monitor ACARS and VRS. I have not looked into that as much. It may require multiple dongles to cover the entire spectrum used, since there are multiple ACARS channels. So one thing at a time,

By putting the unit outdoors, I will only need one ethernet cable coming into my place.

The rtl-sdr LNA (be sure to get the filtered one and not the wideband) has plenty of filtering and amplification.

It’s probably easiest to use with the NeSDR SmarTee or the rtl-sdr v3 dongle to provide power to the LNA.

The rtl-sdr LNA has an initial high pass filter --> amplifier -> SAW -> amplifier -> SAW.
So that’s quite a bit of filtering, perfectly sufficient i’d say.

I haven’t seen any comparisons for combining it with the ProStick+ vs non amplified receivers.
But there are setups that combine those and doesn’t seem detrimental even if one might suspect it to be with so much amplification.

In any case i probably wouldn’t get another filter on top of that.
That would only be warranted if you have a mobile tower on the house next to you.

Normally you find a gain that works for you and run with that.
Matter of fact is, with any rtl-sdr compatible receiver your dynamic range is quite limited.
If you absolutely go for max range, planes closer than 5 miles at low level will no longer be received due to overdrive.
So it’s always somewhat of a compromise.
To get around that compromise you need a better (and more expensive) receiver like the airspy mini.
But when you adjust the gain to receive a helicopter passing 1 mile from your location, i’m sure you can still get 230 nmi or so?
It will depend on your setup.
Also not sure how much you will be able to do with gain, the FA ProStick+ LNA might start overloading from closeby aircraft.
Again i haven’t run that setup, so i really can’t say exactly.
I’d probably recommend just using a rtl-sdr v3 which then even can supply the power for the LNA.
It’s a system i’ve used and i’ve had good results with it as have many others.

Okay, so you think I’m best off a general purpose RTL-based dongle as opposed to one of the Flightaware receivers, which is specifically designed for ADS-B (Or at least is filtered and amplified for ads-b)?

If I am going to use one of those, I’d probably go with the RTL V3, just because I’m already familiar with it. Unless the NESDR Smartee would somehow offer better performance

I live near an airport, so I do want to get stuff that is extremely local. I’d rather not lose local signals, even if that means I don’t get the most distant stuff.

With the v3 you need to do some software shenanigans to activate the bias-t, that might be considered a drawback if you don’t like that.
https://www.rtl-sdr.com/getting-the-v3-bias-tee-to-activate-on-piaware-ads-b-images/

No upside to the nesdr smartee except for the bias-t always providing 4.5 V.

Should be easy to adjust the gain to your liking.
It’s usually not an issue.
(but there is lots and lots of discussion about it, because hey that’s something easy to tweak and check for changes)

Yeah that makes the whole setup quite a bit less complicated as you don’t need the external bias-t anymore to inject power for the LNA.

Just make sure you get the filtered LNA and not the non-filtered variety :slight_smile:

I’ve tried both dongles and prefer the SMArTee for its simplicity. The biastee voltage is always on. The RTL biastee has to be turned on each time the dongle is powered on.

I have the FA antenna, RTL-SDR LNA, SMArTee, RPi4 mounted in my attic.