FlightAware Discussions

Anyone using the RTL-SDR LNA?

I’m considering swapping my Pro Stick Plus for an Airspy Mini and wondering what LNA to put in front of it. I know the HABamp is very good but also looking around, I see that there’s an RTL-SDR LNA which was released last year.

Is anyone using one, how good is it and would you recommend an additional filter in front of it?

Thanks.

i use the RTL-SDR LNA. it has performed very well. i am not sure why an additional filter would be required. you would get more out of band rejection but additional attenuation at 1090MHz.

from what i have seen in your new setup you should have very low loss from antenna to the airspy mini so the 27dB of gain in the LNA may be a bit much. i have about 10dB loss from my antenna to the mini ( i am using LMR400 but have a pretty long run)

With an Airspy Mini, yes, I think it’s needed.

Having seen how well the new setup is working, I now want to upgrade my own receiver here and I think a naked Airspy won’t be as good. I can always wind the gain back to prevent overloading.

As above - Inserting a couple of dB attenuation at 1090 shouldn’t be a problem because I’m expecting plenty of signal. My current receiver here is a Pro Stick Plus with the original FA filter which is (as I now know) useless in the UK really. The new one would help block GSM which surely has to be good?

It has 3 filters.
High pass on the input and 2 SAW filters following each amplification stage.

Putting a filter behind it wouldn’t hurt but probably doesn’t help either.
The only reason for installing a filter in front of it would be installing it on a mobile phone mast or something along those lines :slight_smile:
(Amplifying in two stages helps avoid oversaturating the amplifier with out of band signals i believe)

Understood - I hadn’t noticed that it has three (!) filters built in so I won’t bother with that, thanks.

I wouldn’t say it is useless, it all depends on where the main source of interference is.
I got a good improvement using the original filter over the ProStick plus on its own. This was because it removed very strong broadcast FM and DAB that despite the filter in the ProStick plus was still causing a problem. Here are the graphs from when I added the original filter in May last year.


I further improved things later on by removing the original filter and replacing it with a cavity filter that also removed the local mobile phone signals, but the original filter was a really big improvement over the ProStick plus on its own.
Currently I have 2 stations under test, one a ProStick plus, the other an airspy mini. Both are fed from the same antenna system with an RTL-Sdr LNA. The LNA is powered by the airspy mini and the ProStick plus is fed by a 20dB directional coupler to account for the gain difference. The airspy performs a bit better than the ProStick. The airspy however is running on an odroid xu4 the ProStick on a raspberry pi.

1 Like

While it seems to be working fine for many people, the website says 50 mA on the airspy bias-t.

The rtl-sdr is 150 mA and while it works i changed to an external bias-t to be on the safe side for the higher temperatures in summer.

1 Like

Agreed, I also have an external bias-t that I am intending to feed the amplifier from. In fact there is still quite a lot of re-jigging that needs to be done before the hot weather arrives. Having said that it has started to get pretty warm here already. :slightly_smiling_face:

1 Like

I’ve ordered the RTL-SDR LNA and also an additional bias-tee injector to power it.

/edit - Also got an Airspy mini on order :slight_smile:

1 Like

I use a dongle rtl sdr v3 with rtl sdr lna with 8 m cable H155
I have a Good results

I lived in the UK for five years and I remember that summer was the best day of the year!

2 Likes

Very nice range!

On first glance it looks like you are running too much gain.
What gain do you use?

With that combination you should be using a gain of 20 to 30 at least in my experience.

And I missed it by a day, when I visited the UK.

Here in Canada we have two seasons. We are digging out of winter, and entering the construction season.

3 Likes

Thanks I use the gain 36.4
I have the Best results with this setting

I’ve had good luck with bias tees like this one. I just use a USB “Y” to power it and the Pi.

1 Like

Here’s what it looks like in the box and it’s all gone up today.

The radius on the coax between the Airspy and the bias-tee looks tight but there’s no pressure on the connectors, it’s just the right length. Everything is secure and there’s no way anything can move. Power is via PoE and I’m taking a 5v feed from the Pi for the bias-tee.

Also attached is a one-wire temperature sensor and I just need to work out a way to integrate the readout from that into my graphs so I can see what the temperature is like in the box.

It’s only been back on for a few hours but if you’re interested, you can see a live feed via my VRS here. I probably still need to tweak the gain.

5 Likes

I got 2 of the rtl lna planning to put them outside on my antennas shortly do i need to get a weatherproof box for them…

Regards Lino…

Yes.
They are not intended to be out in the weather. There is no attempt to weather proof them.
Also, SMA plug and sockets are not waterproof.

Do you think just wrapping them with self fusing tape would work, starting and ending the wrap on the cable?

Maybe add a little roof to protect the contraption from the sun.
(something like a can with open bottom and a hole at the top.)

It would work for a while, but I can see problems.

  • Mine runs pretty warm in free air, so a layer of rubber would keep it very hot inside. (even keithma thought it could use a heatsink)
  • The trouble with self-amalgamating tape is that anything inside will be destroyed before you know you have a problem if any water does get in. (don’t get me wrong, I love the stuff)