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If somebody were to setup a pirate radio signal that was broadcasting static would the people tuned in to that frequency be able to tell?

Assuming that there was nothing already on that frequency what kind of equipment would one need to be able to tell that this static was being broadcast and was distinct from the static that occurs in absence of any signal.

I’m assuming that if people tried to use that frequency and found that their signal was being jammed they would know and could triangulate.

Is there some measure of power that would come through or would the broadcast static be indistinguishable from no signal?

Kevin Reid AG6YO
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user2193122
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  • A friend in the Army once told me that he could potentially target the oscillator in a crystal-controlled wristwatch if he was close enough. Any emission can be DF'd. As opposed to no signal. There is one exception. If the "noise floor" is higher than your signal output then your signal would not be noticeable. Of course, if you are the military and have multiple transmitters, I suppose the noise floor could be carefully and artificially raised so LPI signals could get through. – SDsolar Mar 07 '18 at 20:14
  • All that being said, the OP says this would be on a frequency where there is no other legal transmitter. So I would think the risk is very low that anyone would notice or care. I worked as a broadcast engineer for many years and all I cared about was that "my" signals went out as intended. In the scenario in the OP, the answer would depend on whether your white noise was above the noise floor. But with so much QRN out there it would be difficult to distinguish it as being intentional as opposed to natural. – SDsolar Mar 07 '18 at 20:38
  • WARNING: Interfering with any licensed service is a legal offense, and the FCC has plenty of options such as confiscation of equipment and levying of fines. Heed this. ESPECIALLY if you are a licensed ham. I am not aware of any legal cases against people jamming Part 15 devices such as garage door openers. Your OP is silent on your intent yet still take this warning to heart. (Trust me, you do not want to be a test case - they are expensive) Being licensed and jamming a licensed service will bring higher punishment than if others do it. JAMMING is illegal if it targets licensed services. – SDsolar Mar 07 '18 at 20:44
  • @SDsolar FCC, assuming US. Poster did not specify country. – Jim MacKenzie VE5EV Mar 07 '18 at 21:56
  • True enough, but that basically would be true anywhere that follows the rule of law. – SDsolar Mar 08 '18 at 00:56
  • Thanks for all answers! This is really good info and will give me a lot to think about. After reading these answers I can see that my original question was lacking in precision. One thing I wonder about now is "would there be a difference between transmitting a recording of white noise on a frequency vs. having the transmitter just spew out the noise". I think that my original question would involve transmitting white noise at the same level as the ambient static - but I don't know enough about radios to state this correctly. Thanks again! Lots to explore here. – user2193122 Mar 08 '18 at 19:34
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    Let me add that in 2003 when we invaded Iraq, the enemy jammed our GPS systems until we had targeted enough transmitters that it stopped. 'nuff said. – SDsolar Apr 11 '18 at 03:12

2 Answers2

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The station would not really transmit static but rather white (or perhaps pink) noise. This would sound like static but as the observer tunes across the transmitter's frequency, the static would increase notably in volume (assuming amplitude modulation) and decrease again as the transmitting bandwidth is passed. Any signal strength indicator on the receiver, such as an S meter, would also indicate the received signal. These would be clear indicators to the observer that this is not simply atmospheric static or internally generated thermal noise.

The source of the signal is easily found using standard direction finding techniques since there is still an observable signal from the transmitter.

Glenn W9IQ
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  • @SDsolar depends on the observed bandwidth! If your observation is limited to 160 MHz, I can give you any PSD you like (assuming it's power-limited) – Marcus Müller Mar 07 '18 at 21:20
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It really depends. In wireless communications, it's often the case¹ that the majority noise is actually happening in the receiver – which is why you'd want a low noise figure on your receiver. So, there's usually no "broadcast static" – the majority of that noise power happens in your receiver, not on the air. Many receiver architectures will increase the sensitivity if there's no strong (intended) signal in the air, leading to amplified noise, too.

In these bands, the pure presence of an increased noise floor would give away the presence of a broadband interferer.

Now, things aren't quite that easy in general: Whilst a single "non-jammer" interferer usually isn't white in spectrum as what you describe as "static" would usually be, a sufficient number of summing interferers with random properties would both be white in spectrum and gaussian in amplitude distribution, making the detection of your jammer harder.

However, receivers with multiple receive paths cannot be deceived: Your transmitter would be detectable to transmit from a single direction, and thus, if you, for example, add up the signal from two antennas with just the right phase, you could isolate your transmitter well, because they constructively add with that phase, but cancel out with other phases. That technology, both in receive and transmit direction, is called Beamforming, and it works with any signal (note that the receiver noises in both receive paths are independent and never add up constructively, whereas the artificial jamming signal is correlated on both antennas). It's basically a form of triangulation. You can also do the same with distributed antenna systems that coordinate their observations in a central point, so that you can do trilateration.

On large scale, that belongs in the category of things that you'd typically do to do radio surveillance for signal intelligence, airspace security, or cellular infrastructure coordination. So, that's broadly employed wherever there's industrialized areas.

So, if you try that, especially with high TX power, prepare for a visit from your local regulating body, asking you very nasty questions. It might be a criminal offense, depending on which bands you interfered with and where you are.

¹ HF, if I remember correctly, being the most prominent exception
Marcus Müller
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  • You are definitely right about HF. At 10 MHz, the ambient noise figure is in the neighborhood of 60 to 80 dB. https://ham.stackexchange.com/a/9833/218 – Phil Frost - W8II Mar 07 '18 at 22:42