Using USB-VGA dongles as SDR transmitter
laforge.gnumonks.org
laforge.gnumonks.org
"Before transmitting any signals with an FL2000 device, it is strongly suggested that you check the resulting spectrum with a spectrum analyzer, and apply proper filtering to suppress any but the desired transmit frequency.
Operating a transmitter with the unfiltered FL2000 DAC output attached to an antenna outside a RF shielding chamber is dangerous. Don't do it!"
Square waves = theoretically infinite harmonics at positive multiples of the fundamental frequency (in practice reducing with order of the harmonic)
Then there's in-band spurs / spurious emissions, different from harmonics.
There is no way that a simple passive filter will pick out the wanted signal, while blocking all the others.
It would take a sophisticated multi-stage active filter to even come close.
The "very same equipment under control of its official driver" won't have an amplifier and antenna connected to its output. If it did, it obviously would fail its EMC test approvals process.
Forgive me, but this seems quite a blanket statement to make of the tens-hundreds of millions of VGA cable and LCD/CRT designs and design combinations in deployment for the past 30+ years around the world, equipment combinations that never did (and never will) undergo system testing to verify there aren't, in fact, thousands+ of unintentional transmitters deployed already, by people who haven't a clue about their aberrant devices.
It's not like you can't buy dirt-cheap $5 unshielded ultra long VGA extender cables by the literal truckload off AliExpress and eBay, and that you don't find such cables strung vertically to 640x480 projectors hanging off the ceiling of just about every conference center, lecture hall, hotel business suite or similar meeting venue known to man.
Meanwhile this project is explicitly about creating a transmitter in an environment where it is understood by every user upfront the result could be noisy
The idea that you’re pushing here, that there should be varying degrees of a radio equipment prohibition is anti-knowledge and only serves to strengthen the spectrum monopoly businesses.
Usually how enforcement happens is that someone complains that this one spot never gets a signal, or their phone always cuts out. Then the big players start getting involved to determine the problem and either get the fcc involved if needed or otherwise inform the offender to get I fixed.
That's how stories like this happen, https://www.engadget.com/2016/05/25/florida-man-fined-48k-fc...
EDIT: to add there's a lot of unintentional interference sources, neon signs are a typical culprit as they age, http://www.signindustry.com/neon/articles/2004-02-16-RadioFr...
At least in the US, there are already people doing it and anyone who gets caught is subject to massive fines, e.g.:
https://www.computerworld.com/article/2474412/data-privacy/g...
https://www.engadget.com/2016/05/25/florida-man-fined-48k-fc...
That said, anyone should indeed be filtering their output unless transmitting more than extremely low amounts of power (perhaps someone with radio experience could give a hand of thumb? Up to hundreds of microwatts sounds quite safe) as a matter of civility. Besides, you get to learn basic electronics by building a simple passive filter!
GPS is quite easy to jam with very low power. Something as low as 500mW could easily disrupt a fairly wide area. The reason being that GPS signals are generally already below background noise as measured from the ground.
Even with the first tests with 10mW in my room, iPhones at my house picked up GPS signal to know the time and timezone, which caused my flatmates to miss appointments and many websites stopped working due to certificates being expired by "2030".
Both numbers are correct, but 25W isn’t “insanely powerful”. The spec for GPS satellites lists the antenna gain at 13dBi. 25W fed through a 13 dBi antenna is just shy of 500W EIRP. Sitting near me is a 2W 2.4ghz amp and a 24 dBi parabolic antenna. That combo is just over 500W EIRP. The reason you stated (distance) is the big factor, over 12,500mi, the free space path loss is huge (182dB assuming flat gains). 500W is just shy of 27 dBW, so 27-182 is -155, which is a very very very weak signal.
Today, the Solt transmitter in Hungary operates at 2 megawatts.
https://en.wikipedia.org/wiki/Border_blaster
https://en.wikipedia.org/wiki/John_R._Brinkley#Brinkley_and_...
Low earth orbit satellites are much closer to the Earth, so transmitters need less power to cover the range with high quality signal. For example, NOAA satellites are able to send images of the earth at 5W that you can reliably receive with a dipole and a $5 amplifier.
Geostationary satellites are significantly higher, ~35000 Km, but stationary (duh), so they benefit from high gain, very directional antennas both on the satellite and the ground. They send high data and symbol rate signals for HD video of hundreds of channels, and each transponder sits at 15 to 150W (depending on many factors: band, area to cover, etc). They tend to have multiple transponders, though.
GPS satellites sit in the middle, pretty high up, so there's a ton of free space loss, in a non geostationary orbit, so high gain antennas are useless, plus receivers are supposed to be portable, hence there's no room for helix/axial antennas or arrays on the ground. So for this reason they have to ramp up the power to geostationary, TV broadcast levels, only to push a very, very slow data rate (50 bits/s).
A few milliwatts can easily block the sensitive input of a Police Repeater on the other side of town.
FWIW, your "Hundreds of Milliwatts" are routinely used by hams to communicate world wide.
And no, a simple bandpass filter WILL NOT clean up this rubbish. Its output spectrum is the base-band signal repeated over and over, all the way up to VHF. It would take a very capable filter to pick out the single product required. This is NOT the way to design a clean transmitter.
It will not only cause interference, but it will interfere with EVERYTHING within range.
Most output filtering is a simple Low-Pass Filter which is designed to remove harmonics. But by definition, harmonics are an octave removed from the fundamental. This horrid device puts out a closely packed comb of spurii from DC to daylight. A simple passive filter will not even come close to cleaning it up.
You first start with a sound design, then add filters to clean up the last of any unwanted emissions. Not the other way around.
And because these faults have been well documented, this equipment would most definitely be classed as an "intentional jamming device".
> FWIW, your "Hundreds of Milliwatts" are routinely used by hams to communicate world wide.
Read again, I've written "hundreds of microwatts" :)
And that's for a reasonably wideband signal! A narrowband signal with high power has a lot more potential to interfere with a specific application. I seriously doubt anything of that order specially with a rough bandpass (passive) filter around the frequency of interest can cause significant interference. Passive filters have <1 gain, so they shouldn't risk narrowband amplification of the weak signal. The background noise should be within this order of magnitude, no?
(I don't quite have the time to give numbers right now, but here's a source from quick googling: https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7833115 -- the ambient noise should be on the other of .1 uW / GHz; at a few hundred meters away this competes with our wideband microwatt-scale transmitter?) I'll see if I can do some actual calculations later
> "The troublesome transformer was not replaced, but the building owner agreed to turn off the sign should problems arise"
This is a recent investigation that I found particularly intriguing. It involves a device used to monitor electric utilities that ended up interfering VZW's signal in Silicon Valley.
They send out certified letters. Here are a few:
Then they will be on your doorstep within hours. Complete with a search warrant and fines of thousands of dollars, along with a permanent criminal record.
A friend who broadcast on an FM frequency that's unused locally (broadcasting family-friendly Christmas music, I might add) got shut down by the FCC, who sent out people out in the evening to have a chat with him. They care, even when you're not fucking shit up for others. I have no idea what experience you might be basing your statement on, but traditionally the local HAM guys will take offense at any little thing that comes to their attention and the FCC will be happy to follow up on it. (I know at least one local HAM who has lightened up a bit about this stuff over the years but I don't think the feds have)
When it comes to oddball noise, they'll act pretty quickly if there's someone like a busybody HAM to spell out to them exactly where the interference is coming from. Of course, plenty of times it's a HAM who is causing the interference...
The unshielded hardware lab prototypes emitted noise that stepped on the signal of the hardware team's favorite FM rock station. So they tweaked the clocks to be a little slower.
Then they forgot they did that.
Then benchmark time came around. And the new product wasn't up to spec. And tweaking it back up made it unreliable.
Ferrite cores and shielding boxes are your friends, and your investors' friends.
One application I can imagine is to build an osmo-fl2k transmitter that looks like a USB memory stick, ask someone to plug it into the projector computer at church, and then record the video stream with the lyrics. Most projectionists have been helpful and willing to share their PPT files so I can study Chinese, but some are refusing to share them because of copyright issues. The translated songs were not officially licensed, so they're refusing to distribute their data. It is usually possible to ask someone to plug in a USB device (e.g. "to charge"), so if that's a possible entry vector then it would interesting to develop the transmitter further.
EDIT: it looks like it's just the chipset and it's not sold directly - instead, one should look for devices based on it. I wonder if they have any competition, or whether I can just safely assume that any USB3.0 to VGA dongle will work.
EDIT2: Also found this:
> If they are advertised with 2048 × 1152 maximum resolution and support for Mac OS X, or only have a USB 2.0 interface, they contain a DisplayLink chipset and are not compatible with osmo-fl2k! The price range for the FL2000-based adapters is $5-15, whereas the DisplayLink devices typically cost more than $25. Also note that devices sold with USB type C connector contain a different chipset (e.g. Realtek RTD2166) and are just DisplayPort to VGA converters.
Plenty to be found on Amazon or eBay. See the coverage on the RTL-SDR.com blog[0] for a few links.
> EDIT: it looks like it's just the chipset and it's not sold directly - instead, one should look for devices based on it.
Yes, that's correct. You need a USB 3.0 to VGA adapter that is based on the Fresco Logic FL2000 chipset.
[0] https://www.rtl-sdr.com/osmo-fl2k-a-tx-only-sdr-hacked-from-...
PD: I bought as a cheap way to plug a old VGA monitor as a secondary screen, plus allow using it as a SDR transmitter is a nice extra.
Let's consider the figure of 140MS/s x 3 (RGB) x 5 bits per sample (instead of 8 due to noise). then it would constitute about 2.1 Gb/s...
Apparently you can get 10Mbps over a distance of a kilometer or so.
At the same time, I hope this doesn't result in abuse of the spectrum followed by tightened regulations on the cheap dongles.
Please be responsible
This DefCon talk: https://www.youtube.com/watch?v=fQSu9cBaojc
Gives a good overview of why you need tx to capture an IMSI - without forcing a handset into transmitting non-encrypted, you only get the TMSI (unless you can crack the crypto - and why bother, when a base station can instruct a handset to just not encrypt anything?)
It is perhaps more interesting for use as a data exfiltration technique. Simple devices, usually used without analysis, can punch out a signal which is easily decoded, with a simple (and seemingly accidental) antenna.