Background noise while receiving CB localy

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bimbalas
Posts: 2
Joined: Tue Apr 12, 2016 2:55 pm

Background noise while receiving CB localy

Post by bimbalas » Tue Apr 12, 2016 3:11 pm

Hi guys,

Most probably this is not directly related to SDR, but I'll take a chance risking to post into incorrect forum. Feel free to throw a rock at me (because of layman question as well) :)

Alright, so this is my current setup.
Receiver: RTL-SDR with default antenna connected to tablet (no power source attached, minimizing chance of noise)
Sender: handheld CB radio with small whip antenna, battery pack (no ext. power source again)

While receiving test transmission from a different room, there is extreme level of noise, almost killing original transmission sound. Can't figure out what/who is causing such a background noise.
Could it be somehow possible, that transmitter is way too close to receiver? Any other possible sources of that ugly noise? Could it be because of antenna, being totally unsuitable for CB frequencies (~27mhz)? Don't have an adapter for different type of plug yet, so can't test that right away... Oh and I don't have ferrite rings to put on SDR cable as well yet, even though I don't think this would drastically change the situation.

Any ideas would be very welcome.

Sorry once again for stupid question- just can't figure it out myself and can't understand that way too scientific literature :)

Kenn
Posts: 51
Joined: Fri Apr 08, 2016 8:43 pm

Re: Background noise while receiving CB localy

Post by Kenn » Tue Apr 12, 2016 9:50 pm

Not a stupid question at all. I presume you're using SDR#? Make sure you're in AM mode and try reducing the gain. You're so close it might be overloading the receiver.

-- Kenn

bimbalas
Posts: 2
Joined: Tue Apr 12, 2016 2:55 pm

Re: Background noise while receiving CB localy

Post by bimbalas » Thu Apr 14, 2016 6:29 am

Hah, that's a relief :) thanks Kenn.

Thanks for the reply and some ideas. Yes, always using the same modulation on both sender and receiver, of course. And indeed, reducing gain did improve receiving quality quite a bit! It was set to auto before, so might have been screwing around... Even though I'd expect gaining main signal as well as noise, so my transmission wouldn't get lost in noise. Sounds like yet another wrong understanding.

And while playing around, got some more interesting observations... Things got even better when moved receiving antenna into the middle of the room- I believe metal structures in the walls were doing no good (not sure what exactly from physics point of view though). Further more, sender antenna positioning has huge effect (which makes perfect sense now, just didn't pay much attention before). And the last interesting observation I've got- everything more or less works on AM modulation, but when switched to FM- no joy at all. Now that's totally not understandable for my little mind :)

That's pretty much it, waiting for better antennas to come to continue experimenting ...an what the hell was I doing in school back then, eh? :)
Kenn wrote:Not a stupid question at all. I presume you're using SDR#? Make sure you're in AM mode and try reducing the gain. You're so close it might be overloading the receiver.

-- Kenn

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