SDS100/SDS200: SDS100 Missing Parts of Transmissions on NXDN System

[upstatesc]

Recently I've noticed my SDS100 has started missing parts of transmissions on our local NXDN Trunking system.

For example, Friday night I was listening to the scanner and the local PD called in a traffic stop. The officer started giving the info and then suddenly the audio cut out and the scanner went silent. A few seconds later Dispatch confirmed they heard the traffic, and gave the officer back the license info from their database.

This has become a frequent occurrence where either part of a transmission just totally drops off, or I miss one side of the conversation or the reply completely. This behavior happens when I "Hold" the scanner on a talk group too, so it isn't just an issue of the scanner being in scan mode and missing the traffic. I don't have Close Call or any Priority functions enabled, so it can't be that either.

I considered the fact that it may be encryption, so I even loaded the OpenScanner firmware (since it allows you to actually hear the garbled audio of encrypted traffic even though you can't understand it) but the same occurred with it loaded.

Has anyone had similar issues? I've discussed with one other user the possibility that it could be a case of units being on a different site than the dispatch is, and because I can't receive the "site" they're on I'm not hearing their response. That kind of makes sense to me, but that still doesn't explain why things are dropping off mid sentence during transmissions.

The only visual thing I've observed in these situations is that sometimes during a transmission the scanner's RSSI value with fluctuate drastically. It usually sits around -87 with stock antenna, but at times it will jump back and forth between -87 all the way down to -109 during transmissions.

Could that just be the signals coming from the tower itself, or could that be a sign that something is wrong with the scanner itself?

I welcome any input or ideas anyone can offer. The system worked fine back in June with full reception and no issues. I haven't listened much since that time, so this issue has only popped up (to me at least) in the past few weeks.

 

[werinshades]

How about a new frequency or frequencies were added to the site and the new channel ID(s) (LCN) need to be added?

 

[dave3825]

You have a link to the agency in the db? If you’re hearing clear and it drops mid sentence it’s not encrypted. It’s most likely a reception issue.

 

[tvengr]

How many sites do you have programmed?

 

[upstatesc]

How many sites do you have programmed?

There are 4 total but I can only pick up 2 of them. It does appear there has been a change in the past few months to the structure. In the beginning all sites carried all traffic, but now I find that only one of the 2 sites I can receive carry certain talkgroups. I understand that may result in some missed traffic, but it doesn't explain the dropping off in the middle of transmissions.

 

[tvengr]

but it doesn't explain the dropping off in the middle of transmissions.to

Do you have scan delay set to a negative value?

 

[upstatesc]

Do you have scan delay set to a negative value?

Nope, I have most channels set to 3-5 seconds but the behavior is the same when "locked" on the channel/TG

 

[tvengr]

Have you tried all of the filters and IFX? You may have an interfering transmitter that just went on the air. Any new FM broadcast stations? Any TV stations just change frequencies? Did you need to rescan your TV?

 

[Ubbe]

The officer started giving the info and then suddenly the audio cut out and the scanner went silent. A few seconds later Dispatch confirmed they heard the traffic, and gave the officer back the license info from their database.

The only visual thing I've observed in these situations is that sometimes during a transmission the scanner's RSSI value with fluctuate drastically. It usually sits around -87 with stock antenna, but at times it will jump back and forth between -87 all the way down to -109 during transmissions.

SDS scanners use a very poor receiver chip that replaces hundreds of components that does the same thing in a conventional non-sdr scanner. It makes it much quicker to produce the circuit board and less costly compared to a "normal" scanner". The problem are that the $0.75 chip can't handle the complex and dynamic RF situation in a scanner as it is designen for a static situation of signal levels from a satellite or terrestrial broadcast that have a constant signal level and frequencies arre not being scanned.

That receive chip isn't sensitive enough for scanner use so Uniden added a preamplifier and the result are that the receiver gets overloaded very easily and de-sense and loose its receive signal if any strong transmitters are detected withing some 10MHz of your received signal.

That's the nature of Unidens SDS scanners and you can try to use another filter setting. If you now use Normal then try Invert. If that doesn't help then one solution could be to use an external notch filter to block that strong interfering signal. The Waterfall function might show where that strong signal are in the frequency band.

/Ubbe