SDS100/SDS200: Two SDS-100s, two different RSSI readings

[sacscan]

My friend bought his SDS-100 over a year ago. I did the programming for him. About a month ago I bought my first SDS-100 and did identical programming. I left the filter settings default on both scanners (Global Auto Filter: Normal, Site Filter: Global). Both scanners have the stock antenna and latest firmware (Main: Version 1.10.00, Sub: Version 1.02.01). His almost always has RSSI readings 10-20dBm higher than mine on our local 800 MHz Motorola P25 Phase 1 system, yet I very rarely miss transmissions and my radio runs circles around my BCD436HP when driving past cell towers. The 436 loses the control channel, but my SDS-100 keeps on talking.

We tested both radios indoors, outdoors, and while driving. We both lose the control channel near some cell towers, but his usually finds the control channel before mine does as we drive away from the tower.

After reading about some of the hassles others on here have gone through trying to get defective radios exchanged, I really don't want to have to send mine back. Especially if I'll just end up with the same problem again and be out $$ for shipping and insurance. Have any of you experienced this with identical radios, antennas, and programming? I remember back in the CB radio days there were radios with "stingy" meters (they read too low) and radios with meters that were more "generous". I'm hoping my SDS-100 just has a "stingy" RSSI meter

 

[MStep]

My take is that since the SDS series are not "precision" (as in test bench) instruments, there are going to be those types of variations in stuff like RSSI readings. As long as your radio has essentially the same "ears" as other SDS100's, (and your ATTenuation is not accidentally turned on), I don't believe that you are experiencing anything abnormal.

RSSI and S-Meter type readings are meant for the individual user who might want to make adjustments in his/her antenna system, compare relative signal strengths from different stations, and stuff like that. I've had many different types of radios over the years that were the same in every respect, except that they measured signals a little differently, although they "heard" the signals the same. By the way, in my old CB radio days, those meters that were "stingy" were called "tight" meters.

It's a matter of calibration, and look at the bright side--- there is a 50/50 chance that yours is calibrated more accurately than your friends.

 

[jonwienke]

Any comparison thst doesn't use a single antenna feeding both radios is a waste of time. You're seeing differences in the antennas and their positions as much as any actual difference in the radios.

 

[n1chu]

At the risk of nit-picking, I assume when “cell towers” are referred to in the original post, it should read “sites”. I realize some cell towers are shared with other radio services, where public safety, business, ham, etc. use the same tower also but it’s generally considered a site as opposed to a cell tower which relates solely to mobile telephone, a service that scanners can’t monitor by design.

 

[GTR8000]

At the risk of nit-picking, I assume when “cell towers” are referred to in the original post, it should read “sites”. I realize some cell towers are shared with other radio services, where public safety, business, ham, etc. use the same tower also but it’s generally considered a site as opposed to a cell tower which relates solely to mobile telephone, a service that scanners can’t monitor by design.

Sounded to me like he meant exactly what he wrote, and was indeed referring to cellular phone tower sites. The implication being that the signal from the cellular transmitters is causing overload to the scanner, resulting in loss of signal from the 800 MHz trunked system control channel. But, I could be wrong....

 

[sacscan]

Any comparison thst doesn't use a single antenna feeding both radios is a waste of time. You're seeing differences in the antennas and their positions as much as any actual difference in the radios.

I swapped antennas and positions between the two radios. Same result.

Sounded to me like he meant exactly what he wrote, and was indeed referring to cellular phone tower sites. The implication being that the signal from the cellular transmitters is causing overload to the scanner, resulting in loss of signal from the 800 MHz trunked system control channel. But, I could be wrong....

You're right. I was talking about overload from cellular signals. That's been a problem since the days of our old analog 800 MHz Motorola Smartnet trunking system.

I bought the Remtronix REM-820S with the scanner. When I used that antenna I missed more transmissions while driving near cell towers/sites. I figured my scanner was getting overload from those sites so I put the stock antenna back on. It does better in those areas now.

I made sure I never had ATT on, so the difference in RSSI readings wasn't caused by that

 

[jonwienke]

I swapped antennas and positions between the two radios. Same result.

Its still not a valid test method. Because you're not comparing the same signal picked up in the same location at the same time, your results can be skewed by transient radio keyups, one radio generating RFI that interferes with the other, and a variety of other things. The signal going to both radios has to be equal for the comparison to be valid, and different antennas in different locations aren't ever going to pick up equal signals.

 

[nessnet]

What Jon is saying above is 100% correct.
Unless you are in a controlled test environment, any comparisons between different radios is not going to be valid.

EX: using a quality multicoupler like a Stridsberg and a signal generator. Preferably in a Faraday cage.....

 

[Ubbe]

The receiver chip in the SDS100 are obsolite and the SDS200 had to use the upgarded replacement with another model number. If the scanners where manufactured with some years apart they could have a slight variation in their specification, especially if later SDS100's has the new chip. There's no promise from Uniden how accurate the signal strenght readings are and I imagine that they calibrated the values initially at the beta phase and never touched that again.

How it reacts to overload scenarios migh also be a bit different depending of from which batch the receiver chip comes from, how wide it receives signals in it's front end and at what exact level it starts to overload. That's also something that are not specified or promised from Uniden how well it should perform. The only thing said, from UPman, was that if you do not need the simulcast capability you'll probably be better off using a different scanner.

SDS100 test

SDS100 interference test

/Ubbe

 

[jonwienke]

The receiver chip in the SDS100 are obsolite and the SDS200 had to use the upgarded replacement with another model number.

So explain how SDS100 scanners are still being produced, then. They didn't just make one big batch of them back in 2018...

 

[rcool101]

Amazing how "experts" here can comment about the 100 and 200 and don't even own one

 

[GTR8000]

Amazing how "experts" here can comment about the 100 and 200 and don't even own one

I have more experience with the SDS200 than most, and I technically don't "own" one because I didn't personally pay for it out of my own pocket. That's like saying a Ferrari mechanic has no clue about Ferraris because he doesn't own one himself...utterly ridiculous straw man argument.

 

[KevinC]

A little off-topic, but the RSSI difference between my 100 and 200 on a700 MHz system is about 10-12 dB. And before anyone jumps on me, they are using the EXACT same antenna, same site, same filter, no attenuation and the comparison involves moving the coax from the 200 to the 100 (using a SMA to BNC adapter). The 100 purchased a little over a year ago and the 200 in the last 2 weeks. The 100 reads about 10-12 dB higher (better).

 

[GTR8000]

And I have seen the same thing with two SDS200 that are sitting side by side on the same multi-coupler, same jumpers, etc. Same exact programming, same system, slightly different RSSI. Even swapped the jumpers around to eliminate that, same results. But since I didn't pay for them out of my own pocket, I guess those results don't count, huh?

 

[MStep]

Electronics manufacturers like Uniden change parts, specifications, suppliers, companies which produce circuit boards as contractors, and more, depending on their needs at any particular time. So of course they can continue to produce the product, but it does not mean that every single part will be identical in the same model since radios are usually produced in "batches".

Of course, all of this information is held very close to the vest. They are not going to make public when a chip has been changed for better or worse (and especially in this community)--- they simply do their best to produce a finished product which is within the parameters of their original design specifications.

I think Ubbe's post (#9 in this thread) is pretty much on point. I would imagine that if you disassemble an SDS100 from the first or second month's production cycle versus those that were produced more recently, you may likely find parts from different manufacturers.

And GTR8000, I agree wholeheartedly--- you don't have to "own" a radio to know a radio. I am willing to wager (on the risk of some backlash here), that there are folks who follow these discussions that know more about the SDS series than half the folks who actually own one--- me included !!!

And let us not forget the fine print that accompanies most electronic products--- something along the lines of that famous legal disclaimer notice, "Design and specifications are subject to change without notice."

 

[ofd8001]

It's like shopping for clothes - even though you pick out two pair of jeans with the same size and same brand, you'll try them on because variations occur.

 

[Ubbe]

So explain how SDS100 scanners are still being produced, then. They didn't just make one big batch of them back in 2018...

Either they secured a big batch of receiver chips from the last batch produced or they switched to the same chip as in the SDS200 that have additional modes added to it, for UHD sat signals that migh require slightly modificated firmware.

/Ubbe

 

[jonwienke]

Either they secured a big batch of receiver chips from the last batch produced or they switched to the same chip as in the SDS200 that have additional modes added to it, for UHD sat signals that migh require slightly modificated firmware.

/Ubbe

The fact you don't know which is the case shows your previous comment to be uninformed speculation.

 

[Ubbe]

As Rafael has ceased production of their R836 receiver, that where originally used in the SDS100, since almost 2 years ago means that Uniden have done either one or the other to be able to continue to produce SDS100's

Any user that has a newly bought SDS100 can send a STATUS command to his SDS100 to interrogate what receiver chip are in the scanner.
Proscan and possible also ARC have a function to send user commands. R840 are the new chip used in SDS200.

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/Ubbe

 

[KevinC]

Any user that has a newly bought SDS100 can send a STATUS command to his SDS100 to interrogate what receiver chip are in the scanner.
Proscan and possible also ARC have a function to send user commands. R840 are the new chip used in SDS200.

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/Ubbe

What command would that be?