SDS NOISE

kb1tbu

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Hello! I have the sds200 detailed view turned on and it shows the noise. Normally when scanning it reads 38,000 to 40,000. When a system comes on it could range from 60 to 400. What would be acceptable? How to tell where the noise floor is and how much noise I have on the feed? I'm also using a 15 db cable amp with the scanner. I've noticed it helps weak signals come in better. Would this be hurting the noise floor or the scanner?
 

GTR8000

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An amp is going to raise everything, including the noise floor.
 

Ubbe

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When trying out antennas, amplifiers and external filters you should look at the noise level for analog channels and D_ERROR for digital systems and totally ignore the RSSI and signal strenght bars as those could be looking at a 10Mhz wide frequency span and not only the monitored frequency. Also when using amplifiers it will increase the signal strenght but it is the noise level that you want to be as low as possible or you are only adding more noise to your reception. If you are using the full 15dB amplification you probably are overloading the scanner, or very close to it. I have different scanner brands and no scanner can take more than a 6dB gain, at the scanners antenna port and using no external filters, without loosing sensitivity. The best way to set gain level are to use a variable 20dB attenuator after the amplifier and adjust it for best signal quality, the lowest noise or d-error value.

I would think that a noise level of 1000 would the max where noise becomes annoying. Remember that when someone talks or there are other sounds in the transmission it will increase the noise level. The noise number will only indicate a more or less steady vaule when there's a carrier without anyone talking. That could make it difficult to see any changes you make to your setup and it's probably best to use your ears with analog signals and the d-error value for digital as the digital stream are modulated at a constant level.

/Ubbe
 

kb1tbu

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Sep 5, 2012
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When trying out antennas, amplifiers and external filters you should look at the noise level for analog channels and D_ERROR for digital systems and totally ignore the RSSI and signal strenght bars as those could be looking at a 10Mhz wide frequency span and not only the monitored frequency. Also when using amplifiers it will increase the signal strenght but it is the noise level that you want to be as low as possible or you are only adding more noise to your reception. If you are using the full 15dB amplification you probably are overloading the scanner, or very close to it. I have different scanner brands and no scanner can take more than a 6dB gain, at the scanners antenna port and using no external filters, without loosing sensitivity. The best way to set gain level are to use a variable 20dB attenuator after the amplifier and adjust it for best signal quality, the lowest noise or d-error value.

I would think that a noise level of 1000 would the max where noise becomes annoying. Remember that when someone talks or there are other sounds in the transmission it will increase the noise level. The noise number will only indicate a more or less steady vaule when there's a carrier without anyone talking. That could make it difficult to see any changes you make to your setup and it's probably best to use your ears with analog signals and the d-error value for digital as the digital stream are modulated at a constant level.

/Ubbe

If I was overloading the scanner, would it be making any weird sounds? It seems to be running just fine. If I'm overloading it, I cant tell. I also added a moca filter on the line with a 5-45 return block also.
 

Ubbe

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If I was overloading the scanner, would it be making any weird sounds?
When you start to overload a scanner it will loose sensitivity but you will not notice anything else happening. If you overload it too much it will start to create intermodulation products that will make strange noises and you hear two transmissions at the same time and transmission apperar on the wrong frequency. But that happens long after you have lost reception sensitivity.

/Ubbe
 

kb1tbu

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ok. I'm using a diamond x300N antenna with 60 feet of RG 11 into the scanner. I did notice cleaner signal with the amp, but I don't want to over load. Do you think its worth the risk?
 

kb1tbu

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Sep 5, 2012
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I unplugged the amp for now just to see how things go without it. I've ran the amp for about a week now, think I did any damage? Things sound ok without it on. Still pulling in the same stuff, just weaker.
 

Ubbe

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You can't damage anything when using a preamp, you could only degrade performance while using it and will not create permanent damage to a scanner.

/Ubbe
 
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