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Author Topic: What is that crackling noise?  (Read 2701 times)
KD6OJG
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Posts: 38




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« on: November 04, 2013, 04:38:30 PM »

I'm still learning about all things Ham radio and I am going to ask a question that I've always hesitated to ask, because it seems like a really simplistic question...When you turn your rig on and you're just monitoring any given frequency and the squelch is turned down and you here that steady crackle that's always there --- What is it?  Sometimes it is very low and at other times it's almost deafening.  Even when you hear someone transmitting and their signal is strong and their voice is crystal clear, that crackling is always there, even underneath their voice.

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K1CJS
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« Reply #1 on: November 04, 2013, 05:42:25 PM »

Background noise, better known as the noise floor.
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AA4PB
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« Reply #2 on: November 04, 2013, 05:47:43 PM »

If you are hearing the noise even when a strong signal is present then it is more likely external noise being picked up by the antenna, perhaps generated by leaky insulators on power lines. Try disconnecting the antenna and turning the squelch down. What you should hear then is more like a steady "hiss" which is noise generated by the components in the receiver.
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KD6OJG
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Posts: 38




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« Reply #3 on: November 04, 2013, 05:57:27 PM »

Background noise, better known as the noise floor.

Oh...thank you so much.  Now I have term and description to work with and research.

Here is my next question; Is this something that you can get rid of or is it just the nature of things and always omnipresent in radio communications?

Thanks,
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AA4PB
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« Reply #4 on: November 05, 2013, 05:24:12 AM »

It depends on the noise source. If it's created by leaky insulators on the power line then the power company can eliminate it. If it's just the internal receiver noise then you just have to live with it. Like I said, try disconnecting the antenna and let us know what the noise level does.

What equipment, band, and mode are you talking about?
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K1CJS
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« Reply #5 on: November 05, 2013, 05:49:29 AM »

Background noise you just have to live with.  Usually it isn't of any consequence and the incoming signals will easily override it.  Just turn the squelch up a bit to stop the noise if it bothers you.

Now, if the noise is deafening and the squelch won't block it without blocking the incoming signal as well, it's more than simple background noise.  You're best bet in that instance is to see if you can contact an experienced ham or club in your area--who may already know what the noise is, and how you may be able to work around it.  Good luck and 73.
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AA4HA
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« Reply #6 on: November 05, 2013, 10:32:34 AM »

Its the galaxy!

Everything generates electrical fields (the Lesser Magellanic Cloud, air blowing through the trees, fish, rain, the Sun). All of that contributes to the noise floor across the entire electromagnetic spectrum. We call it the floor because it is the base level of signals at a specific frequency (it does change depending where you are in the EM (electromagnetic) band).

In the HF spectrum (3 MHz to 30 MHz) you will hear it rise and fall throughout the day. Usually the noise is greatest during the day when the energy from the Sun swells up the Earth's geomagnetic field (ionosphere). Going higher in frequency to VHF (30 MHz to 300 MHz), to the UHF (300 MHz to 3 GHz) the noise floor changes.

We would test radios in "screen rooms". These were specially designed enclosures known as "Faraday Cages" where there was minimal outside RF interference and noise. When you closed and latched the door you could hear the decrease in the background hiss on the radio under test. It allowed for us to align receivers using signal generators or to operate transmitters without the signal causing problems for licensed users.

Better receivers introduce almost nothing to the noise floor. They have selectivity that is good enough to narrow down their receiver to just what we wanted to listen to. So much of the debate about who has the better radio is centred around how good the receiver is at providing gain (amplification), selectivity and immunity from intermodulation (mixing of other signals that create a signal where it was not intended).

Different modes of operation will also have a different noise component. FM radio like what many amateurs use on 2 meters and 70 sounds very different than AM or SSB voice. FM requires a much stronger signal for reception, SSB is usually the best voice mode for lower signal levels.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
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