SDS100/SDS200: SDS100 - Squelch Not Opening Occasionally

[trentbob]

So attenuating a frequency simply reduces or eliminates overload or splatter. You can do it on an individual frequency or you can do it on a global status affecting all frequencies in the radio, use the quick method to toggle it on and off, while holding on a frequency hit function and a quick tap on the number 4 key, you can also press function and hold the number 4 key this will give you global attenuation. The only problem attenuating a frequency if it's in the distance like you say 20 miles, it will compromise the reception and maybe not break the squelch when other radios do.

Another thing you can do is use IFX which you can toggle on and off by sitting on the frequency you want to apply it to and toggle function 7, that is only applied to the frequency you apply to but it's Global for that frequency, anywhere that frequency may be in the radio. Here is a description of IFX from the man himself Paul Opitz RIP. He was the product manager who designed the SDS 100 and 200 and he passed away in December 2019.

 

[werinshades]

Location is Rockingham County, New Hampshire. I am not monitoring any trunked systems at all. The majority of what I monitor is P25 conventional. Those P25 conventional frequencies are where I see the problem. It might happen on the analog as well but I don't monitor them very often so it's hard to say for sure:

Rockingham County, New Hampshire (NH) Scanner Frequencies and Radio Frequency Reference

Scanner Frequencies and Radio Frequency Reference for Rockingham County, New Hampshire (NH)

www.radioreference.com

There was a part of this that I intentionally did not mention earlier because I didn't want to lead the responses but here goes: I will often be holding on a P25 frequency and see that the SDS100 is not opening squelch despite my other scanners doing so. In other words, I know there is an active transmission but the SDS100 isn't doing anything. If I simply use the scroll knob to rotate up one channel and then immediately go back to the problematic channel... voila! The problem is solved and the squelch opens. That sounds ridiculous so as it was happening today I took a video. In it you can see my SDS100 side by side with my BCD396XT. Both are holding on Derry Fire Dispatch / Operations (see Rockingham county link above). The quality of the video isn't anything to write home about unfortunately but such is life.

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Can you load your programming here? I watched the video and am confused why this is happening because the signal appears to be good. Have you tried listening with the stock antenna only and away from all the other scanners.

 

[Ubbe]

There's a tower 1.25 miles from my house ...

... if I don't have the attenuator turned on for them, I'll often get high digital error rates on their frequency.

But I'm not totally sure what to do here which is in part a lack of my understanding in how the attenuator works.

The problem in the SDS100 receiver begins to accelerate at -60dBm and stronger signals. If the signal strengths of what you receive are all -70dBm or stronger then I recommend to always use attenuation, set it to global. If the signals in the 800MHz band are weaker down at -80dBm then only set attenuation to the other frequency bands, that can be done per site in trunked systems but needs to be set per frequency for conventional systems. But it's easily done in Sentinel by copy and then paste a whole column.

The attenuator are reducing the whole antenna signal to the receiver. If you scan and it's scanning a frequency that have been set with the attenuator enabled it will reduce the signal while that particular frequency are monitored in the scan cycle.

The signal level detector in SDS100 are operating over a wide frequency bandwidth, something like 10MHz wide, and not only from the exact frequency you are monitoring. If you listen to 153MHz then a 155MHz signal can have an impact on the RSSI value. There's also an automatic gain circuit in the receiver that sense the signal level within that 10MHz window and reduce its sensitivity to try and cope with overload issues. It works well for TV and satellite signals that are 7-10MHz wide but not suitable for narrow 25Khz and 12,5Khz signals and it's function will have an unwanted impact on the scanners function, where other scanners do not have any problem, and that AGC are a fixed built in function that cannot be disabled in this TV/SAT receiver chip, it's hardware related and cannot be fixed in software.

For digital signals it is always best to use the bit error display to set the lowest errors while trying different settings of attenuator, IFX and filters, and ignore what the RSSI says as it will also indicate the level of the interference that you are trying to reduce.

/Ubbe

 

[andy404ns]

Haven't noticed much thus far after playing around with the filter settings.

Just applied the firmware update that was released so I'll give that a week or so to see if anything improves.

Am I correct in my understanding that the BDC436HP would not have this problem because it is not SDR based like the SDS100? i.e. It would perform the same as my BCD396XT in terms of reception / digital decoding?

 

[werinshades]

Haven't noticed much thus far after playing around with the filter settings.

Just applied the firmware update that was released so I'll give that a week or so to see if anything improves.

Am I correct in my understanding that the BDC436HP would not have this problem because it is not SDR based like the SDS100? i.e. It would perform the same as my BCD396XT in terms of reception / digital decoding?

Take the SDS100 off the multicoupler and run it on its own antenna. Does the issue persist? How strong are the signals?

strip it down to the stock antenna and work your way up..

Did you try any of these suggestions?

 

[andy404ns]

Did you try any of these suggestions?

Yeah I carry it around with a handheld antenna several hours a day. I don't recall seeing the problem happen but it's a bit hard to tell because when I'm mobile with it I don't have my other scanners to compare. So if it is missing stuff, I wouldn't necessarily realize it. That said, it seems to be better when not connected to the external antenna so I think the problem is overload from these strong signals as a few people have suggested.

The problem for me is that since I use it both as a "base" and a handheld, I can't attenuate the frequencies that have trouble with the external antenna because when I go mobile I won't pick them up at all. The obvious answer here is to simply not connect to the external antenna and instead keep the handheld antenna on it at all times.

 

[andy404ns]

The more I think about it, the more I realize I'm using it in a way in which it's not really intended. The best course of action is probably to buy a new desktop scanner to dedicate to the external antenna and I can attenuate signals as needed with it. Since I don't have any simulcast systems in my area, the SDS series really doesn't offer much so I can save some money and go with a 536HP. Then the SDS100 can be relegated to strictly handheld/mobile ops.

 

[werinshades]

Yeah I carry it around with a handheld antenna several hours a day. I don't recall seeing the problem happen but it's a bit hard to tell because when I'm mobile with it I don't have my other scanners to compare. So if it is missing stuff, I wouldn't necessarily realize it. That said, it seems to be better when not connected to the external antenna so I think the problem is overload from these strong signals as a few people have suggested.

The problem for me is that since I use it both as a "base" and a handheld, I can't attenuate the frequencies that have trouble with the external antenna because when I go mobile I won't pick them up at all. The obvious answer here is to simply not connect to the external antenna and instead keep the handheld antenna on it at all times.

Glad you were able to get it to work.

As far as the mobile vs base set up, you can copy the favorite list, rename it something like County A (Base), County A (Mobile), give them each their own Quick Key (County A-Base 98/County A-Mobile 99). This way you can attenuate one and not the other.

I agree...desktops are made to use on desk, and handhelds are mobile. If you do go with the 536 and experience the same issue, you'll be able to resolve it.