How to read the RSSI meter on an SDS200?

Marauder

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Something I am having a hard time finding info about in the manual is the RSSI meter. I am still pretty new to anything more than a BCT 8 and just trying to figure this radio out now so please excuse my ignorance but I assume it stands for resistance. Is a smaller or bigger number better?

I notice that it is measured in negatives? I see the"-" before the RSSI number when someone keys up.

Thanks!
 

radiopro52

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The RSSI meter measures signal strength. The closer the number is to "0", the stronger the signal. For example, an RSSI of -50 is a stronger signal than a reading of -75. A reading of -100 is extremely weak.

From my observations though, the signal strength readings (especially the signal meter) are very inaccurate.
 

Marauder

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The RSSI meter measures signal strength. The closer the number is to "0", the stronger the signal. For example, an RSSI of -50 is a stronger signal than a reading of -75. A reading of -100 is extremely weak.

From my observations though, the signal strength readings (especially the signal meter) are very inaccurate.
Got it. Thanks for making it easy to understand!

And yes I agree. I was looking at the number fluctuating from the -70s, -110s and wasn't really hearing much of a difference.
 

radiopro52

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Got it. Thanks for making it easy to understand!

And yes I agree. I was looking at the number fluctuating from the -70s, -110s and wasn't really hearing much of a difference.
I start noticing complete signal drop outs when it gets below -110dBm. Anything above that though seems to be fine on digital transmissions.

The signal meter reads a full 5 bars for an RSSI value of -95dBm and above, which is still very weak. However I think the intention of the signal meter is to show if the signal is strong enough to properly decode, rather than show actual signal strength.
 

n1chu

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RSSI stands for Received Signal Strength Indicator. And yes, it seems to be erratic. But it’s a place to start... and as answered, a value of -50 is a better reading than -100. What this means in relation to the S Meter reading is a bit complicated. I just take the RSSI value with a grain of salt. I’ve played with the various filter settings on my SDS200, looking to see if any choice makes a difference in the RSSI value and to date, haven’t concluded much of anything. But it seems to be one of the factors needed to be considered when choosing any particular filter setting, or none. I’ve set my Global Filter to Off, individual trunking sites to off along with the conventional dept’s in an effort to turn off all filtering. I did that in an effort to return to basics. Now I will try different filters looking for improvements.
 

n1chu

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Is RSSI just a method of determining how close a digital signal is to the threshold between hearing and not hearing? An analogue signal can be heard as a weak signal, staticky, in the weeds, when reaching its limits. A digital signal doesn’t have those characteristics, it’s either there full strength or not at all.
 

ansky

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The strongest signals on my SDS200 register at -60. I have never seen anything stronger than that.
 

nessnet

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I’ve set my Global Filter to Off, individual trunking sites to off along with the conventional dept’s in an effort to turn off all filtering.
To turn off all filtering easily,....
If you have everything (conventional depts / trunking sites set to global, and then set the main global auto filter to off, you have turned all filters off.
 

Ubbe

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The strongest signals on my SDS200 register at -60. I have never seen anything stronger than that.
I injected the strongest signal I could from a signal generator and it didn't go above -40dBm, which is 2000uV, a pretty strong signal where you have to be very close to a site to receive or use a high gain antenna and perhaps an amplifier.

/Ubbe
 

Marauder

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RSSI stands for Received Signal Strength Indicator. And yes, it seems to be erratic. But it’s a place to start... and as answered, a value of -50 is a better reading than -100. What this means in relation to the S Meter reading is a bit complicated. I just take the RSSI value with a grain of salt. I’ve played with the various filter settings on my SDS200, looking to see if any choice makes a difference in the RSSI value and to date, haven’t concluded much of anything. But it seems to be one of the factors needed to be considered when choosing any particular filter setting, or none. I’ve set my Global Filter to Off, individual trunking sites to off along with the conventional dept’s in an effort to turn off all filtering. I did that in an effort to return to basics. Now I will try different filters looking for improvements.
I have recently disabled my filter as well. I set it to normal and it scans like lightning compared to auto. I wish I had done so earlier. It was very hard to scan multiple sites going so slow. Still isn't as fast as an older bearcat but it's close enough.



The strongest signals on my SDS200 register at -60. I have never seen anything stronger than that.
Same experience here. I have yet to see a lower number
 

Ubbe

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I have recently disabled my filter as well.
To disable the filter setting and make it work as in a non-SDS scanner you have to set it to Off.

There's always a filter involved and when having it set to Off will make it totally symetrical and it will receive signals within something like +/-5MHz and will have it's best sensitivity with the lowest loss. Normal setting are a high pass filter that will pass frequencies at around -1MHz +9MHz from the monitored frequency. If you have a strong transmitter at +8MHz it could interfere with your reception and sometimes even totally block it out. You then have to use Invert that pass -9MHz and up to +1MHz. But if you then have another strong transmitter at -5Mhz you could still be interfered. Then the Wide settings can be used that only shift the filter half ways and Wide Normal setting will pass frequencies between -3MHz and +7MHz making it avoding both interferencies to have an impact on your reception. Also Wide will have less attenuation and digital waveform distorsion than Normal/Invert. In weak signal situation try to use Off and then Wide and lastly Normal/Invert to use the best possible sensitivity and cleanest digital signal.

It's almost impossible to know when a frequency are strong enough that it will interfere so filter settings will always be a trial and error excersise.

/Ubbe
 

Marauder

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To disable the filter setting and make it work as in a non-SDS scanner you have to set it to Off.

There's always a filter involved and when having it set to Off will make it totally symetrical and it will receive signals within something like +/-5MHz and will have it's best sensitivity with the lowest loss. Normal setting are a high pass filter that will pass frequencies at around -1MHz +9MHz from the monitored frequency. If you have a strong transmitter at +8MHz it could interfere with your reception and sometimes even totally block it out. You then have to use Invert that pass -9MHz and up to +1MHz. But if you then have another strong transmitter at -5Mhz you could still be interfered. Then the Wide settings can be used that only shift the filter half ways and Wide Normal setting will pass frequencies between -3MHz and +7MHz making it avoding both interferencies to have an impact on your reception. Also Wide will have less attenuation and digital waveform distorsion than Normal/Invert. In weak signal situation try to use Off and then Wide and lastly Normal/Invert to use the best possible sensitivity and cleanest digital signal.

It's almost impossible to know when a frequency are strong enough that it will interfere so filter settings will always be a trial and error excersise.

/Ubbe
Would this explain why I can hear my local malls 464.8750 security walkie talkies on my old BCT8 and not my SDS200? It has been bugging the crap out of me how a 600 dollar scanner isn't getting what an old >100 dollar scanner is getting on the same antenna. (No PL tone per RR DB)
 

Ubbe

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Would this explain why I can hear my local malls 464.8750 security walkie talkies on my old BCT8 and not my SDS200?
It could be if you are using a similar type of antenna and you are at the same location as when you use the BCT8. Did you try all possible filter settings as well as IFX? You could add a lot of extra departments in that system with just that single frequency but each department has a different filter setting and you include all departments in scan to see if any of them will get reception when your BCT8 does. If none of the 5 different filters help then stop on the frequency, or enter it by channel+freq+channel and function+7 to set IFX to it and scan those departments again. If you scan other systems at the same time then set the frequency in each department to DND priority. If the BCT8 starts to receive then turn the SDS200 dial to leave any current conversation on other systems and it should engage priority scan.

The money wasn't spent on the receiver hardware as the receiver chip in the SDS200 sells for $0.75 at Alibaba. A receiver that can handle simulcast transmissions and still be a good performer costs 3 or 4 times more than a SDS200 and then you do not get all the decoding features and scanning capabilities, if you look at AOR and Icoms receivers in the $3000 range. Uniden wouldn't sell enough scanners to cover the development costs if they tried and sell a scanner in that price range. They had to cut corners and go cheap to keep costs down. SDS scanners still works satisfactory for most people but it isn't the best one for weak signal scanning or when you have RF interferences close by.

/Ubbe
 

kruser

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Is not dBm value more or less a calibrated level where as an RSSI reading can be any value a manufacturer wants?

I've seen cell phones display RSSI readings in test mode before that simply ranged from 0 to 100 where 100 was max signal.
dBm on the other had was a calibrated standard as far as I recall. A lof of people tried to use the old S-x readings from CB radio meters. That's another uncalibrated standard but is often taken from a point in the radio that may be close.
 
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