FlightAware Discussions

Anyone using the RTL-SDR LNA?

Agreed, I wouldn’t want to fully encase it in tape. It would need to be multiple layers as well to be waterproof and that’s a lot of insulation.

Hi
I have put aluminum scotch around the corners and the rubber washer , put the nut back after

LFBDBORDEAUX

I put the rtl lna up last weekend just to try it out with no case its been working well the last few days we had lots of rain and i havent had any problems i do have a case and planning to put 3 rtl na in it…

Regards lino…

My UPUTRONICS LNA broke, I’m still working referring warranty and meanwhile I purchased a RTL-SDR LNA, because I also have the RTL-SDR V3 dongel, so I can use the software based bias tee.
Enabling bisa tee via software is very easy ==> https://www.rtl-sdr.com/getting-the-v3-bias-tee-to-activate-on-piaware-ads-b-images/
Using it with dump1090-mutability requires some modifications of the listed commands.

First I put ther LNA just in front of the V3 dongle, works fine, then I put it in front of the ZAPD-2DC+ Power Splitter; works fine too.
The antenna splitter is conected with
(1) Pi 3+ (dump1090-mutability) and
(2) Pi Zero (dump1090-fa).
Antenna is a 5/8 ground plane (Stanislav Palo/SK, via ebay).

I’m very satisfied with the RTL-SDR LNA … :smiley:

(delivery from China took 20 days, no shipping fee, LNA = 26,95 USD)

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dump1090-mutability: bias-t activation

https://www.rtl-sdr.com/getting-the-v3-bias-tee-to-activate-on-piaware-ads-b-images/#comment-99985

Your photo seems to show the V3 connected to Port 2 of the ZAPD-2DC+ splitter.

Does this really work? The Datasheet says it won’t.

Yes, I tried it and it works.
Without LNA (as setup was before) I have ~ 50% less a/c either with V3 dongle (connected with RasPi 3 B+) or RadarBox ADS-B Stick (connected to RasPi Zero).

As I wrote, for dump1090-mutability I added modified commands; see also link posted by @abcd567 bcd567

The question is how the DC passes through the splitter as the data sheet says DC only works with port 2 of the splitter, not port 1.

But i would guess you have v3 dongles on both ports? :slight_smile:

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As shown on the pic:
at port-2: RTL-SDR V3 dongle (dump1090-mutabiliy),
and as written:
at port-1: the green RadarBox ADS-B FlightStick (dump1090-fa).

LNA 'work’s on both.

It’s about supplying the LNA with power.

But @geckoVN looked up the wrong data sheet because you mentioned the wrong device.
According to your picture it’s this one:
https://ww2.minicircuits.com/pdfs/ZAPD-21+.pdf

It supports DC pass through on both ports.
That also means the input of the other dongle gets the 5V as well.
Seems it doesn’t mind, lucky you :slight_smile:

Well spotted.

The protection diode on the input of the FlightStick “should” have clamped the BiasT voltage to ~0.8V … and it probably did … for a while … but no longer.

I have one of these on order at the moment. Currently using an LNA4ALL with a satellite diplexer as a high pass filter (gives better results than the FA filter I have), it will be interesting to compare it.

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Yes, looks like, that the 5 V are going through via output-1 to my RadarBox ADS-B FlightStick doesn’t cause anything … I haven’t thought about that before …

Until now it works … I will report, if it’s not working anymore …
I don’t know, if it works with other dongles too; and not intended to check it with my FA-Sticks … :owl:

The preamp arrived and I’ve swapped it over - something tells me I might need to adjust the gain somewhat:

gain

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I’ve had the RTL-SDR.com LNA installed for a several days now and have accumulated some data.

I am using an RTL_SDR.com v2 dongle. The comparison here is with the LNA4ALL, which was mounted directly underneath a Sandpiper (now available under the Radar-rama name) antenna which is installed in the loft space of my house. I was using a satellite diplexer with 1GHz cut off as a high pass filter. There is approximately 20m of WF100 coax between the amp and the dongle, with the filter mounted next to the dongle. The amplifier is powered by the dongle’s built in bias-t.

Swapping to the RTL-SDR.com dongle, the setup is similar except that the high pass filter is removed and the coax is connected directly to the dongle.

The results are pretty clear - the RTL-SDR.com amp is performing much better. I see more aircraft with it, see higher peak message rates and have longer maximum range. The number of messages received per aircraft is also higher:

Blue is the RTL-SDR.com amp, and red is the LNA4ALL.

There are a couple of things to note.

Firstly, I am using far more coax than I need, because this antenna will be mounted outside eventually. I think that the extra coax length is making the higher gain of the RTL-SDR.com amp more significant than it might otherwise be, since the gain on the dongle is set much lower. This will help reduce noise at the dongle by reducing noise that comes from the coax. The reason I think this is significant is because the gain setting with the LNA4ALL and this coax length was almost at maximum. With a shorter coax I had to use a lower gain.

I have certainly had better results than this from the LNA4ALL before, using my home made franklin spider and a much shorter coax I’ve had results comparable to the RTL-SDR.com amp here. The home made antenna will not survive outside however, hence testing the professionally made one which is much more sturdy but seems to have slightly less gain. I’m hoping the improvement from being out from under the roof shingles compensates for that though.

I will swap my franklin spider back in at some point and compare it against this antenna using the same amp.

My conclusion is that the RTL-SDR.com amp is very good, and well worth it if you want an amplifier to mount at the antenna. My main criticism of it is that it isn’t weatherproof, so mounting it outside at the antenna means you will have to find some way to protect it.

This isn’t really a criticism of the LNA4ALL since that works perfectly well as a wideband amp, it’s just in these circumstances the RTL-SDR.com amp works much better.

Edit:

Something else I have just noticed, that also shows a use for the changes @wiedehopf made to the signal strength graphs - the improvement in effective dynamic range is clearly visible here:

image image

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With so many of the signals normally clipping in the ADC, it’s not really possible to see dynamic range on the graphs.
But i suppose when tweaking the gain to the same percentage of strong signals, you can somewhat compare the weakest signal received by each setup.
That would somewhat show which system allows reception of weaker signals.

Dynamic range is probably not the correct phrase, however it’s definitely possible to see the effect of having the gain set incorrectly - this is the same antenna and amp combination, first with the gain set too high, and second with it adjusted using your autogain script to get <5% strong signals:

image image

The adjusted results show consistent reception of weaker signals.

Actually for the weak signals, using more gain is actually better :wink:

But with more gain you lose some strong messages overwhelming the analog stages of the rtl-sdr stick.

Well yes, but being a digital mode you don’t get an improvement in weak signals once they are strong enough to decode.

While having gain too high can prevent detection of strong signals due to overloading, it does also seem to have an effect on the ability to decode weak signals as well - the day with properly adjusted gain shows better range than the one with too high gain. I’ll try and do some more tests to explore this a bit.

hello caius, here is a photo of my RTL-SDR LNA1090 in a small IP67 “bud box”. the gland nuts (top and bottom are IP68 rated) ,the cable coming from the FA antenna is LMR240 and the cable going out the bottom of the box is LMR 400 (the gland nuts were sized to fit the cable diameters). the two black details you see on the lower left and upper right of the vertical front of the box are ITW enclosure vents. they are also IP67 rated for water/moisture ingress. i mounted these to the vertical front of the box (they MUST be on a vertical surface) to form a chimney to allow heat to escape from the box. they have been thru many very severe thunderstorms with no issues as far as rain getting in the box.