I use the FA-recommended setup. Upgrading my antenna significantly increased (+75%) the # of logged points. I see a lot of antenna questions here, and I can say that the difference was huge.
However, I only see a modest range increase. This leads me to believe that I want more than the SDR stick’s 8-bit dynamic range. Would upgrading the receiver help?
Specifically…
(1) Has anyone used a higher resolution SDR with dump1090? And is there a list of compatible receivers somewhere? I want to be careful because all the ones I’ve found are a big step up in price and I am new to SDR. The FunCubeDongle (http://www.funcubedongle.com/) has 16-bit resolution and claims to work without drivers.
(2) For those who have used amplifiers, have you done a before-after comparison?
Amplifier added 20nm (maybe 10%) to range, and maybe 25% to number of aircraft - I think that was due to bringing aircraft that we within the old range but the signal was weak.
I just use a satellite system LNB amp connected to the base of the antenna and a capacitor + coil type voltage injector by the pi - cost for both was maybe 15USD
Is ADS-B software available for this funcubedongle?
Ive got a similar set up to you Peter but just cant seem to get the satellite amp to work correctly, with the amp inline I notice a considerable drop in the amount of aircraft sighted.
On my next attempt I was going to try & increase the voltage that I am feeding through the combiner, at present I have tried a supply rated 13.8v.
One inexpensive “upgrade” you could make is to get a dongle with a R820T2, however I have yet to find a seller that guarantees that their dongle come with that chip.
As far as amplifiers go, I too am also interested in trying an amplifier. However, the only success stories I have found were from people using SKY amplifiers which are next to impossible to get in the US. Can anyone recommend an amplifier that both works for this application and is easily accessible in the US?
Haven’t learned much more about upgrading the SDR stick itself.
It seems like dump1090 is looking for a 2MHz 8-bit sampled stream. By this requirement (and irrespective of drivers, etc), the funcube SDR dongle is too slow to work (http://www.rtl-sdr.com/about-rtl-sdr/). I wonder if the system can handle other bit depths and rates.
I have seen on other forums where some have tried adding amplifiers to increase a dongle’s sensitivity. It appears to usually fail due to the dongle’s wide bandwidth and appearing to be overloaded by ‘other’ frequencies, possibly the 900MHz cellular radio band. If a 1090MHz tuned filter is used on the antenna side of the amplifier and dongle, the results appeared to be better.
I assume because the dongle is broadband with no tuned filters, strong signals that we aren’t monitoring can overload it quite easily.
While cheap, this preamp reputedly has a 3dB noise figure, which is not much better than the bottom of the quoted range of the RTL2832 dongle (approx 3.5-10dB). At 1090 MHz you can find preamps with < 1.0 dB noise figure, which while costing a lot more should perform better.
A preamp may do you more harm than good. Among other things it could overload the SDR dongle. I’d think that if you’re investing in a preamp you may also want to invest in a bandpass filter too … as most preamps people are mentioning here are fairly wide band.
I’ve got a piaware setup at a mountain top location and its performing very poorly probably due to overload. At home I added the NooElec aluminum case and a bandpass filter and that made a big difference: HF and UHF transmissions at home no longer affect the piaware setup. (I’ll eventually get these installed at the mountain top location as well.)
What I have not done is to find a way to determine what the SDR dongle is seeing in terms of signals at 1.09 GHz - this is on the todo list. (Simple spectrum analyzer software would allow you to do before and after analysis with preamps, filters and SDR dongle gain settings.)
The ADS-B signal itself is about 2MHz wide so you really do need that bandwidth - so as you say, the funcube won’t have the bandwidth unfortunately as it’ll only do up to around 200kHz.
It wouldn’t be terribly hard to adapt dump1090 to handle 16 bit samples, but the bandwidth is the killer problem.
You would be right. If the amplifier is boosting a wide range of signals, it would be very easy to overdrive the receiver. The best way to do it is an amplifier and a filter. In the satcom world we used filters after the LNA and we had to be careful with the attenuation on the downconverter as too little would overdrive the modem and really mess with the level and quality of signal. Mind you, this is a multi-million dollar terminal, not some $20 USB dongle.
I can confirm that a well designed amplifier with a filter and a decent antenna with a decent location will give good results. Far better than without the filter/amp.
It’s my understanding that the Raspberry Pi does its own amplification (or controls the receiver’s amplification. If you add a pre-amp, you need to also reconfigure that amplification so you don’t oversaturate the signal. Someone can correct me if I’m wrong about this.
Anyway, if it is right, the only reason to use a preamp is if its signal to noise ratio is better than what you get using the existing amplifier.
Main reason for a preamp, as I understand it, is to put the preamp close to the antenna so you can avoid amplifying any noise picked up by the feedline.
It also helps to amplify the low power signal before the feed line so the feed line loss isn’t removing too much to use it.
I don’t believe that’s accurate. Gain and amplifying are two different things. Think about squelch on an old CB radio (if you ever worked with one that is). You could lower the squelch to the point you just hear noise or you can raise it to the point you can’t hear anything (even valid traffic). That’s gain.
Using the same CB reference, if you have a signal come in unamplified, it will be at one level… But if you put in an amplifier, it will be higher in power. That’s what the amplifier does.
I don’t believe our dongles have amplification, but they do have gain.
