wield signal on the gqrx, could somebody explain what is this ?

[xi sizhe]

I am very new to SDR and GQRX, recently I just got a rtl-sdr Dougle and played it around with GQRX, the first thing I tried was to look at the FM signals, but no matter how I scanned manually, the signal appeared was always a line, I could not hear anything about the FM stations.

Here is the screenshot of one signal in the form of a straight line, could anyone explain why the signals I received is always like this below

I wondered if it was my dougle went broken?

[Alexandru Csete]

That looks like a spur (a fake signal generated by either the dongle itself or a nearby computer or electronic device). The spectrum is full of them.

In order to receive anything meaningful you need to:

(1) Know where to look for signals in your area.

(2) Use an outdoor antenna (the one that comes with the dongle is usually not good)

(3) Set the input device gain to a proper value (start with auto gain)

In most places you can check your setup using FM broadcast stations in the 88 - 108 MHz (use FM wide).

Alex

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[David Ranch]

I bet I know what this one is...

It's a sound card running on your machine!  Really and I had the same thing happen to me too.  Do the 3rd harmonic math:  48,000hz * 3 = 144,000,000Hz (144mhz).  I bet your frequency offset shown on your Gqrx is due to poorer quality of using an RTL dongle and maybe the soundcard itself too.  I wrote this up some time ago:

   http://www.trinityos.com/HAM/CentosDigitalModes/hampacketizing-centos.html#6a.soundcards

I've personally found other cheap / failing devices creating a lot of RFI on 144.000 as well:  PS2 KB/Mouse to USB adapters, poorly shielded iPod dock radios etc.  If you have one, grab your HAM HT, tune it to 144.000 and walk around the home to find the emitters.  When you think you've found a suspect device.. disconnect the HT's antenna (do NOT push the PTT button) and get REALLY close to the suspect device to confirm.  Btw.. though I tried and no matter the # of ferrite chokes, wrapping device in tinfoil, etc. none of it helped suppress the EMI .  The root of it is that many of these cheap devices have removed their filter networks and are now noise generators!  There are better devices out there though.. read the above URL for some ideas at least for inexpensive USB sound cards.

--David
KI6ZHD

[Clayton Smith]

The spur at 144 MHz is the 5th harmonic of the RTL-SDR's 28.8 MHz
crystal. Have a look, and you'll see similar spurs at all the
multiples of 28.8 MHz.

73,
Clayton VE3IRR

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[Corey Koval]

To add to the list of possibilities: my desktop mouse gives off a spur at that frequency. Its a cheap wired mouse. I was able to minimize it by putting a ferrite bead on the wire.