If you want to power that filter/amp from an external source (rather than up the feedline), you’ll need to remove an inductor or it won’t work
Personally, I think the hassle of enabling the Bias-T on the V3 is well worth the effort.
The V3 plus this filter/amp is a gratet combo, but take note of the suggestion that it is intended that the amp is mounted at the mast-head and the gain level was chosen expecting at least 3dB of cable attenuation before the receiver.
That’s not really a problem when you turn down the gain.
And you need to reduce the gain anyway.
I know what you mean, but turning the gain down is not quite the same as reducing the signal level.
If the amp is saturating the front end, turning the gain down won’t ‘unsaturate’ it.
Isn’t the gain attenuation in front of the “front-end”? 
Or is the gain variable amplification, i guess then you can easily oversaturate the input.
Anyway i’ve seen people running a gain of 5 successfully with an LNA and the Flightaware Pro Stick Plus.
That’s even more amplification and it worked fine.
According to the Rafael datasheet block diagram (not always literal), the input is a variable gain amplifier
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Remember though, that there is a sky 67150 Lna chip in front of the r820t
http://www.skyworksinc.com/uploads/documents/SKY67150_396LF_202922I.pdf
The LNA has a gain of approximately 20dB.
The max input to the r820 is +10dBm so this equates to -10dBm max at the input to the LNA chip.
The maximum output of an ADSB transponder is +57dBm (500W) so you will not hit overload as long as the path loss is greater than 67dB. At 1090MHz that equates to a distance of about 50 metres. So, as long as you are more than 50 metres away from the aircraft you should not have problems with overloading.
This assumes however you have filtered any higher powered transmissions such as FM broadcast out.
With a high gain antenna you can get some more distance.
But for that you need the aircraft at 500 W in the horizontal plane where the antenna has the maximum gain.
If you are gonna use it at an airport such things become a consideration of course.
The bigger practical problem is overloading from things such as FM broadcast transmitters.
Without filtering you need to be more than 5km from a 50kW 100MHz transmitter to avoid overloading the front end of the orange ProStick.
It works out to be about 1.8km for the blue ProStick plus.
The discussion originated about using the rtl-sdr LNA.
More than enough filtering there.
Yes, but with the RTL-SDR LNA in front of a ProStick you have another 27dB of gain so you will now need to be more than 1km away rather than 50 metres when you hit the maximum input level at the R820T.
I agree though that the filtering is good with the RTL-SDR but in some cases the gain may well be too high at 1090MHz.
I actually use the RTL-SDR LNA myself but my Prostick is fed from a 20dB directional coupler so I only have 7dB gain in front of the ProStick but retain the benefits of the filtering.
The full 27dB gain though path feeds an airspy mini that I use for comparison purposes.
/edit
Meant to say. The RTL-SDR V3 dongle effectively has the input straight into the R820T2 so the RTL-SDR V3 plus RTL-SDR LNA is much less likely to suffer overloading at 1090MHz.
The 50 metre overloading distance of the ProStick becomes 100 metres for the RTL-SDR V3 LNA combination.
I have ordered “rtl-sdr LNA with tripple filter”, and will use it with this dongle and and antenna lying disused for last 4 years.
Gents, I can’t fault the logic above, but if it were as simple as that, there should (almost) never be a need to back off the gain.
My V3 + RTL-SDR LNA gives the best performance with an 8 dB attenuator between the amp and V3 (dipole antenna and 10m of dubious RG6).
In my experience signal/noise from LNA is always some xx db. Whether there is any actual RF signal is amplified or not it doesn’t matter. What ever the actual signal it gets is amplified and if the signal is already pretty strong then it is getting clipped. If it is too weak then it wont be amplified and it is lost.
These amps are useful for lengthy cables and also for deaf dongles like mine. A generic one with a nooelec cover which fooled me into thinking it was a Nooelec 
I can see an aircraft coming for landing some 20-30kms away but I can’t see it when it comes any where nearer like 5kms and as buildings block the view I happen to see the signal ones it goes below 500ft.
If ADSB followed the theory of 50 mtrs then I will be happy.
The figures above only relate to the level at which the variable gain amplifier in the R820T starts to saturate. The output of the R820T feeds into an RTL2832U and the signal to that needs to be kept within its operating range. Hence the reason for having to back off the gain. You will overload the RTL2832 if you have large signals and run the R820T flat out.
That is why I have decided to use a generic DVB-T (no integral lna) and mag-mount antenna (gain less than 2 dBi) with “rtl-sdr lna with tripple filter” when it arrives.
That looks like the exact same stick I was using until receiving the RadarBox stick. Should work great.
It worked great from 2013, till I purchased FA ProStick in 2016, and retired it. Since then it is lying disused in my parts drawer.
I’m not sure why you would intentionally cripple the LNA.
Anyway you can later connect it directly to the PCB or FA antenna and use the rtl-sdr v3 stick you have.
That’s what it deserves and i’m fairly certain it will work fine without further attenuation.
(you already have some attenuation of 1090 MHz anyway in the form of a window pane)
No, I dont have rtl-sdr v3. That is why when working out “enabl bias-t” for FR24’s Pi24 image, and for dump1090-mutability v 1.15~dev, I had to use simulation.
