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Loggings => Other => Topic started by: Beerus Maximus on April 15, 2013, 1849 UTC

Title: 16930 KHz (estimated) jammer?
Post by: Beerus Maximus on April 15, 2013, 1849 UTC
I came across this pulsing siren noise on 16930 KHz. Does anyone know what this is? Sounds like a jammer maybe:


First part of recording is in AM, then I switch USB. There may be a very weak carrier at 16932-ish, that could be the target of jamming? Time is 1842 UTC on 4/15/2013.
Title: Re: 16930 KHz (estimated) jammer?
Post by: 07code04stalker1776 on April 16, 2013, 0019 UTC
My first thought is that it Sounds like HAARP (High Frequency Active Auroral Research Program). However the more I listen to it I believe it's most definitely OTHR (Over The Horizon Radar).

What is your (General) Location?

Title: Re: 16930 KHz (estimated) jammer?
Post by: Token on April 16, 2013, 0229 UTC
That is either a sounder (if it was periodic and infrequent) or it is a radar.  My bet would be it is a sounder, specificaly this one:

Title: Re: 16930 KHz (estimated) jammer?
Post by: K5KNT on April 16, 2013, 1329 UTC
In this context, what is a sounder?
Title: Re: 16930 KHz (estimated) jammer?
Post by: Token on April 16, 2013, 1639 UTC
Most of the following is just how I go about it, if you want to categorize things differently than feel free ;)

A “sounder” in this context is an RF based system or device used for atmospheric observation and examination.   It can be an ionosonde, a chirpsounder, a digisonde, a dynasonde, or any one of several other specific technologies.  In a very real sense a sounder is a radar, either monostatic or multistatic, that has a specific target set, the atmosphere and propagation.  It can absolutely be argued that sounders are radars, the term sounder and radar (sounder is NOT universally used) simply serve to differentiate the application.  Many items that I (and others, but the sample set of hobbyist looking at these is not large) refer to as “sounders” are called “radar” by their makers/users.

In the stuff below I am going to generalize systems looking at propagation and atmospherics as “sounders” and systems looking at man made features (aircraft, ships, etc) and surface natural features (ocean waves and currents) as “radars”.

Because of this last fact, sounders are radars for the atmosphere, determining the purpose of a signal that is heard can be difficult with some techniques.

When you hear a “chirpsounder” (http://www.youtube.com/watch?v=B0EwS45ZZbo ) the intent and source is fairly clear.  The same can be said with a digisounder (http://www.youtube.com/watch?v=cX5r-bv4oSs ).  But more complex sounder waveforms (this http://www.youtube.com/watch?v=LfpE4clYlKU this http://www.youtube.com/watch?v=AHeFOwAuMHs or this http://www.youtube.com/watch?v=3jvluq3mBZI ) can be indistinguishable from radars when viewed instantaneously.  Their habits over time can help you establish a probable category.

To tell this last style of sounder from a “radar” you have to define what is being done.  Because a “sounder” instead of a “radar” tends to be interested in what the entire atmosphere is doing it is typically transient in frequency.  It sweeps, hops, or moves, in frequency to sample the conditions across a wide range of frequencies.  HF radars, on the other hand, want to gather data from a specific region (or regions) over time, so they also can change frequency but typically much more slowly, primarily just to use current propagation conditions to illuminate the desired region of the World.

So what are some of the identifiers to distinguish sounders from radars?

FMCW sounders are typically much narrower banded than radars.  Simply, they often do not sweep as wide as most radars in a single FMCW sweep.  There are several performance factors that establish this, but sounders can get away with a narrower FMCW sweep and not be as performance impacted as a radar of the same width would be.  The chirp rate, width, and sweep repetition rate of a radar or of a sounder can all be used to calculate some of its theoretical performance limits (possible max and min speeds for detectable targets, max and min usable ranges, etc).

Sounders typically change frequency often and revisit a given frequency or frequency range at a much reduced rate compared to radars.  A radar may set on a given frequency or frequency range for hours (propagation allowing) to gather data.  A radar typically revisits a set of parameters often, sometimes continuously.  This is driven by the relatively rapidly changing nature of the target set, aircraft and ships move, and can move rapidly, waves and currents less so, but still they change.  The atmosphere tends to change more slowly, so you can get away with sampling it every few minutes, say 2 to 12 times an hour.

Sounders want to sample a large range of frequencies to establish the activities in the atmosphere.  A chirpsounder might start at 2 MHz and sweep up to 30 MHz, charting responses along the way.  Other sounders may pick a spot frequency in different bands and step down, or up, hitting each in cycle, say starting at 30 MHz and stepping down about 1 MHz per step until it gets down to the lower frequency edge, say 3 MHz.  This type of sounder might spend 10 to 60 seconds on each step, repeating a cycle once every 10 to 30 minutes.  A radar typically only makes large jumps when conditions (or interference) make it do so, even frequency hopping HF radars tend to stay in a fairly constrained range of frequencies for a given time period.

So, as a general rule and regardless of waveform used, something that hits a specific frequency or narrow range of frequencies once every few minutes (or longer time delays) is most probably looking at atmospherics.  Something that hits a given frequency or frequency range at a higher rate is probably a radar.

Of course there are exceptions, everything above is just a guideline that I use.  For example the SuperDARN radar is looking at atmospherics, but sounds as frequently as any radar looking for ships or aircraft might, it also stays confined to a relatively narrow range of frequencies at any one time.  Its performance limits, based on pulse shape, width, and rep rates, tell you it is probably looking at atmospherics, while other habits would suggest some other use.  Because it is well documented we know its use, despite the potentially conflicting indications.

Title: Re: 16930 KHz (estimated) jammer?
Post by: K5KNT on April 16, 2013, 2022 UTC
Token, thanks again for a detailed explanation. Your youtube examples are also extremely helpful.  This is one thing I really like about the forums here.  I'm so use to getting short one sentence replies on other forums I visit, this is such a refreshing change.