I know there's at least one radiolad here - tell me about ADS-B setups.
I only really need the bare minimum to get the free flightradar business account, but I'd actually quite like to get decent coverage myself.
What's the 'best' way to do this? I've got enough raspi's knocking about for that to be the easiest route for me, but as ever I'm willing to be swayed to more expensive bollocks.
I also have two different places I could base the receiver - somewhere with decent elevation about 15 miles from the airport, or somewhere in a slight valley but within spitting distance (well, one mile) of the airport. Which is more appropriate?
Also, it'd be quite nice to run a regular SDR alongside that, I know you can do that with an RPi setup, but what would you recommend for a general, occasional poking about on the airwaves dongle + aerial combo too?
>>27107 I have one of these, it's a Kinetic SBS-1 - I've had it for over ten years now. It was originally about 400 quid, and needed Windows, but there are many many more on the market now and I would think you could do no wrong with one of the £25 SDRs; at the time it was about the only device under a grand you could buy. It came with its own Windows app, which allowed you to visualise the results, but nowadays I think just about everyone uses a RaspPI and feeds data to PlaneFinder or Flightrader and uses their visualisation tools.
I have a few SDR's too - my favourite is called the HackRF One, but that's also quite pricey, you can get started with the little USB sticks from Amazon and GnuRadio now. On the cheaper end, I like the NooElec ones too, and have a few of those. You basically need anything with the R820T and RTL2832U chipset, which many of the cheap SDRs have.
One of the advantages of doing it with multiple, cheap devices, is its also easy to pick up things like ACARS; you see some interesting/fascinating things float by there too.
Appreciate the answer, especially the encouragement to go with multiple locations. Once I've charmed them a bit more at the new job I might even get away with sticking one on the ramp at the airport, who knows.
I didn't even think about ACARS, that's very useful. I sort of already have access to that sort of data but not directly - would be genuinely helpful to see that.
Have ordered a twin NooElec dongle bundle for now, and will go from there. Will update with my levels of success later in the week.
I've noticed you can get a HackRF One on eBay for about £140 now - are they weird bootleg versions, or just cheaper than I remember them being? Last time someone (you?) mentioned them on here they were about £250.
Basically, yes. All those sites like Flightradar, Flightaware, Planefinder etc work by pooling a load of receivers that pick up a planes transmission, which pumps out information such as their callsign, ID, location, altitude, and so on. It's functionally a secondary radar and and extremely cheap and effective way to monitor air traffic, both on the ground and in flight.
The cheap HackRF Ones are sort-of knock-offs, because the design is open source.
The HackRF One is certainly the most versatile of the low-cost SDR systems, but I wouldn't necessarily recommend it as a receiver. It has transmit capability and an exceptionally wide frequency coverage which makes it very useful for hardware hackers, but the performance of the receiver is pretty mediocre.
I'd suggest an SDRplay RSP if you only plan on receiving. It's receive-only, but it has extraordinarily good receiver performance and goes toe-to-toe with radios costing ten times as much. It has built-in bandpass and notch filters, so your target signals won't be drowned out by local noise from TV transmitters and the like. It also has good software and documentation, so it's quite easy to get up and running if you're not a radio geek. The base RSP1A model is less than a hundred quid.
Using multiple SDR receivers (even of different types) is no problem; most SDR software can control multiple transmitters or receivers using the Omnirig protocol. You can also use virtual receivers in the SDR software to monitor multiple frequencies simultaneously within the same band.
Antennas are a more complicated subject, because you'll always get the best performance from an antenna that's tuned to a specific frequency band. A variety of wideband scanning antennas are available, which will give tolerable performance across a relatively wide frequency range. If you'll be doing a lot of listening in a particular band, I'd suggest a tuned antenna - there are plenty of inexpensive VHF airband antennas on the market.
Height makes a huge difference, so I'd strongly recommend using the more elevated location. UHF and VHF transmissions can cover distances of hundreds of miles, but a solid obstacle will stop them dead. Getting your antennas up on a chimney breast or in a high tree is also well worth the effort - even slightly extending the horizon will hugely increase your potential to receive distant signals. If you're comfortable with a soldering iron, I'd suggest the books Receiving Antennas for the Radio Amateur or Stealth Antennas, because building your own antennas is really the best option if you're serious about radio.
Thought I'd drop back in to say I'm having very promising results from a homemade J pole antenna mounted at only about 8 feet high. I can get results about 100nm away. Very excited to see what happens once I actually get my arse on the roof with it.
Also picking up ATC very nicely on a different rig, though sometimes it seems like my dongle is being overpowered by the strength of the signal, and it becomes one big unreadable mess? I assume there's some clever active attenuators to be built for this sort of thing, or is that just a limitation of the little cheap dongles?
>I assume there's some clever active attenuators to be built for this sort of thing, or is that just a limitation of the little cheap dongles?
There are two possibilities - either the receiver is being overloaded by the signal you're trying to receive, or it's being overloaded by a different signal within the receiver bandwidth.
In the first case, you can usually just turn down the preamplifier gain or add a passive attenuator, which is little more than a couple of resistors.
The second case is more likely, and more difficult to solve. Selectivity (the ability to isolate one signal without interference from signals on adjacent frequencies) is a really hard problem in radio receiver design. If you try and record a really loud gig on your phone, all you'll end up recording is really nasty distorted bass because the microphone is overloaded. It's the same problem with radio - if one signal overloads the receiver, the distortion can drown out other frequencies. The cheap RTL dongles only have an 8-bit ADC so they're quite easy to overload and they have very little filtering, so they pick up far more out-of-band signals.
A more sophisticated receiver like the SDRPlay RSP has a much higher bit depth, so it can cope with loud signals within the band without having to turn down the gain to the point that you lose the weaker signals. It also has a whole bunch of bandpass filters, so you can block most of the signals outside the band you're trying to receive.
If you're sticking with the RTL-SDR, you can buy or build a bandpass filter, which will significantly increase the receiver performance within that band. Reasonably inexpensive filters for the ADS-B and VHF air bands are readily available.
It sounds daft, but until you mentioned your gig analogy and bandpass filters, I had never made the link between working with audio and with radio frequencies. As I have a masters in Audio Stuff, this will likely help me quite a bit.
I had a muck about at the second location today and you're right about it being case number two - whenever someone broadcasts on the tower frequency I'm tuned to, I get them and the ATIS broadcast a few kHz down the scale at the same time, but only when someone's transmitting, which I suppose I don't really understand.
Experience with Audio Stuff is a huge advantage in radio - most of the basic principles are the same, you just need to recalibrate your intuition to account for the weirdness of high-frequency signals.
>whenever someone broadcasts on the tower frequency I'm tuned to, I get them and the ATIS broadcast a few kHz down the scale at the same time
You might be seeing intermodulation distortion products, but you might also be seeing an unsuppressed image from the RF mixer in your receiver. If it's of interest, the video below does a decent job of describing direct conversion receivers with an IQ demodulator, which is the operating principle of your RTL-SDR stick. I'm not massively familiar with aeronautical radio, but I suspect that the signal from the aircraft is slightly phase shifting due to the movement of the transmitter relative to ground, which is messing with the IQ demodulator and causing an image frequency below the tuning frequency.
