FlightAware Discussions

FlightAware RTLSDR dongle

I was thinking of buying one of these:

It has the pre-amp and 1090MHz filter built in so reduces the number of components required which is great. However I do have a couple of questions.

Firstly, I have built one of these as well as a cantenna:

Am I likely to see any advantage using the dongle with the pre-amp?

Secondly, can the amp and filter be turned on and off in software or are they hardwired? Just wondering in case I wanted to re-purpose the dongle at some point.

Thanks.

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It’s hardwired.

In some cases you need an extra filter before the prostick plus because the LNA can become overloaded.
But in most cases yes it will improve reception compared to cheap DVB-T stick.

In case you get an extra FlightAware filter be sure to get the dark blue one.

Personally i had better reception with the rtl-sdr blog external LNA and v3 dongle. Has all the filters it needs builtin. But it’s more components indeed and the bias-t needs to be enabled in software to supply power to the LNA.

Thanks. This is exactly what I was trying to ascertain. This FlightAware unit costs rather more than a cheap LNA, but it has a certain appeal as a neat all-in-one package. However, since the filtering is hardwired, the downside is that it can only be used to receive frequencies within the filtering band. Including the filtering sounds like a great idea, but there ought to be a way of turning it on or off as required so the dongle can be used as a standard RTLSDR if required.

The RTLSDR.COM dongle was the other one I was looking at. Someone elsewhere also suggested this LNA:

This should work for 1090MHz and 978MHz and the cost of dongle + the LNA above would be about the same, so I was trying to decide which way to go. Although the RTLSDR.COM dongle has been optimised in some ways, it does not appear to be restricted by filtering to 1090MHz. I think that if I’m going to have to pay 30GBP, then I would prefer to go with something that has a bit of flexibility.

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We looked at exactly that but had trouble finding a suitable RF switch where the additional losses didn’t outweigh the benefits of having the filter in the first place.

Use UNFILTERED ProStick (orange color)
For 1090 & 978 Mhz, you can add a Flightaware external filter. For other frequencies, use without the Filter. This dongle has a built-in LNA, but no filter

.

Amplifiers without a filter have their own problems.
You can’t receive 978 MHz and 1090 MHz at the same time with one dongle.

Note that the amplifier you linked require 12-18 V which can’t be supplied by the rtl-sdr v3 dongle (4.5 V bias-t).

  • Remote powered 12-18 V by multiswitch or set-top-box

You’ll have to get an extra bias-t and feed 12 V.

In my previous post i was referencing this LNA specifically for ADS-B but it’s a little more expensive:
https://rtl-sdr.com/new-product-rtl-sdr-blog-1090-mhz-ads-b-lna/

There are some halfway decent amplifiers for 1090 MHz on ebay but i’m not in the loop regarding those.
@SoNic67
Your LNA seems to be acceptable and was probably cheaper than the rtl-sdr LNA?
Which model did you buy?

That’s a good point. I had forgotten about the orange FA dongle.

That is also a fair point, however, I was not suggesting that one could receive 1090MHz and 978Mhz at the same time. A separate antenna tuned to the frequency as well as a separate LNA and RTLSDR dongle would still be required for each frequency, but I figured that the same LNA should work for either scenario since both frequencies are within its passband. However,…

Yes, the power requirement would add further complexity as some kind of PSU would be required. I came to realise that myself a bit later after I had posted. I’m told that one of these will do the job though:

I did wonder whether whether the LA could be modded for a 4.5v bias-t though? Of course, the PSU does add extra cost and the money could be perhaps be better spent on a better and bias-t compatible LNA instead.

Yes, there are indeed a number of LNA devices on eBay, but I am not clued up enough either to be able to determine their relative merits or faults. I can see however that most of the very cheap ones consist of just one semiconductor (FET?) and very few discrete components, whereas the more expensive ones are clearly much more complex in design.

I’m in a rural area so I’m not sure whether the filter is necessary, so for now I should perhaps focus on the RTLSDR + LNA, and think about adding a filter if required later.

The nearest mobile phone tower is maybe 3 km from my position and still the filtered rtl-sdr LNA + rtl-sdr v3 stick was a significant improvement compared to the prostick plus (used with filter).

Compared to broadcast and mobile phone signals long range ADS-B signals are very weak.
The receivers only have a limited amount of frequency separation capabilities in regards to stronger signals interfering with reception.
(The rtl tuner chip is cheap after all, more expensive receivers have better separation)

That is interesting to note. I would say that the nearest tower to me is probably 1km (disguised as a grain silo!). The next furthest would be about 3 or 4 km. Having considered all of the helpful advice here, I have now ordered the RTLSDR dongle and ADS-B LNA with “triple filter” from RTLSDR.COM (sorry FA!) as this seemed the best technical option. Hopefully this will deal adequately with signals from the nearby mobile tower!

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What’s your theoretical range like?
What is the Maximum Range I can Get?

Thanks for pointing out the heywhatsthat.com site. I found it very useful and had come across it already. According to the result, I should theoretically be able to get a coverage of a radius of around 130 miles for aircraft at 10,000ft, and approximately 200 miles for aircraft at 30,000ft. This covers from 2/3 to pretty much the whole of England with the exception of the a few miles at the tip of Lands End. At 30,000ft, I should theoretically be able to pick up aircraft as far as Dublin. Since I am currently getting a coverage of only around 60-70 miles, there appears to be significant scope for improvement. I don’t know whether I will achieve that theoretical coverage, but I am hoping that the kit I have just ordered from RTLSDR.COM will at least significantly improve the coverage that I am currently getting. A radius of 100 miles would be nice!

I wise decision. I tried everything: FA orange and blue dongles, generic dongles, AirNav dongle, FA light and dark blue filters, eBay filter, eBay LNAs.

The best combination, in my case, is the RTL-SDR Blog dongle and LNA.

Don’t forget to order the FA antenna. That one is tops. Also, the power inserter (T-Bias), if you don’t want to deal with software configuration for that.

Hi… actually I’m using a normal software defined radio usb stick (RTL2832) from adafruit in combination with an self-built groundplate antenna to receive signals on my raspberry pi.
Do you think that I can improve the signal strength with the FlightAware Pro Stick.
Specs: Amplifier: 19dB with 0.4dB noise figure and OIP3 +39dB

pcb manufacturing and assembly

Hmmm… why not? I am thinking about a faster dongle that can switch between the two frequencies fast enough.

The airspy does not have enough bandwidth to be able to receive both 978MHz and 1090MHz at the same time. It has 9MHz alias free bandwidth. You would need to have at least 112MHz to receive both simultaneously.

I meant switching between the two feeds.
With 20MHz, you could have 10MHz on each… Not truly 12MHz for MLAT… but close enough.
The Airspy R2 claims " Up to 80 MSPS when using custom firmware"

That’s not how it works, you get the bandwidth in a block around the tuned frequency.

I’m no expert on receiver design so i won’t attempt to explain why, but that’s how it works as far as i know.

You can switch tuning frequency pretty fast. If the dongle could do it more than 2x the desired signal bandwidth, you can sample both places alternately (not simultaneously).

But yeah, it was more of a rhetorical question.

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It’d be technically possible but

a) you’d need to write a hybrid demodulator that fed samples to either a 1090 or a 978 demodulator according to the current tuning; this software does not currently exist.

b) if you went for, say, a 50/50 split then you’d see approx half the message rate on both bands; there is no predictability about when signals are going to arrive, so you can’t schedule when to switch. In practice you’d see less than half because the act of retuning takes some non-zero time during which you’d not receiving either band.

This sort of thing really only makes sense when you have some sort of TDM in the radio protocol that lets you expect signals on a particular frequency at a particular time. Neither 1090ES nor 978 does this (1090 not at all; 978 has some time slot functionality but it appears to be aimed more at avoiding collisions than at having predictable transmission times). Or if you’re scanning for a signal that’s going to hang around for a while (e.g. looking for airband AM)

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… but why bother.
If the RTL chip were $1k each, it’d be worth considering.
Given the actual cost, a two-chip design makes a lot more sense.

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