SDS100 Minor bug

[jonwienke]

Just for giggles, I was listening to some local broadcast FM stations with the SDS100. On some stations (generally ones with a RSSI higher than -60dBm) the audio would cut out periodically, almost like I had WX Priority or Close Call (not Do Not Disturb) active, except that the cutout was not as regular--the time between cutouts varied from 3-10 seconds or so. When the audio cut out, the RSSI would show "---" as if the RF signal had disappeared.

This only happens with FMB and strong local stations. I haven't heard it on anything FM or NFM.

 

[bob550]

Overload protection circuit activating?

 

[RF23]

Does using the ATT. help?

 

[jonwienke]

Nope. Attenuator knocked the signal from -50 to -70dBm, but the signal still dropped occasionally. Today the spacing between the dropout varied from 5 seconds to 5 minutes. I tried switching to WFM and only had one dropout in 10 minutes. It seems that wider channel width puts more load on on the CPU, which causes the dropouts.

 

[buddrousa]

Jon this is acting like a clip from the fm station and the receiver is sensitive enough to see.

 

[jonwienke]

The 436 doesn't drop the channel, so it's not on the broadcast end. The only thing that makes sense is a CPU loading issue on wider channels CPU power required is proportional to the channel width.

 

[JamesO]

Seeing similar behavior on an SDS100 as well however, finding it on a few FM stations that show around -75 dBm on the signal level. Not sure overall signal level is the issue as I ave other stations will similar signal levels or higher and they do not drop out.

Seems to only be happening on my local 107.3 FM station and it does not happen in my 88.5 FM station which has a -68 dBm signal.

Unclear if there is something going on HD radio or a sub carrier on this 107.3 FM station.

 

[KR7CQ]

I was thinking about the HD radio sub carrier while reading this also.

 

[Ubbe]

You didn't mentioned anything about squelch settings. Does it drop the signal the same way if you have the SQ set to its normal value or fully open? Try setting the frequency a little offset 50KHz up or down and check the result.

/Ubbe

 

[jonwienke]

Squelch was 2. It doesn't cause channel drop under any other conditions. I tested several broadcast FM stations with similar results. The only thing that made a difference was selecting WFM instead of FMB. Instead of dropping every 5-10 seconds, it was more like 5 minutes.

 

[racing1]

You didn't mentioned anything about squelch settings. Does it drop the signal the same way if you have the SQ set to its normal value or fully open? Try setting the frequency a little offset 50KHz up or down and check the result.

/Ubbe

Would fully open be 0?

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[JamesO]

I was able to turn the squelch from 2 to 1 or to 0 on the 107.3 FM station that was dropping in and out and it seems to have stabilized the signal. But then playing around a bit more, seems that the actual squelch threshold is not really a "critical" setting.

I can play with the squelch and require the signal, then run the squelch all the way to 15 and the station will play for a while, but then drop in and and out a bit. It is not consistent in time and I am not moving around so the signal should be pretty stable.

The FM Broadcast band appears to sound like the filtering may not be the correct width?? I did set the step size to 50 kHz and moving the center frequency +/- 50 kHz the signal dropped out totally.

FM sounds a bit ratty and I do not think it is the speaker, because the sound quality is still a bit "ratty" from what I would expect.

Will play around a bit more over the weekend and see if I can determine what is actually happening. I have a few spectrum analyzers and can run an external antenna split to the radio one or more spectrum analyzers to view the spectrum and see what this station may have for sub carriers and such.

Also wondering if Uniden will ever offer the ability for this radio to be able to monitor North American Digital TV sound.

 

[Ubbe]

In other scanners there's always a seperate IF discriminator chip connected before the FM and NFM filters that is handling the FM broadcast reception. In SDS100 it is a software defined receiver doing it all and it can be tricky to have a filter design that allow both narrow band 12,5KHz and WFM 150KHz using the same components.

Muting completly when going 50KHz offset indicate that something is designed too narrow and broadcast FM reception have probably been put in there just as an extra gimmick not having the same quality as the rest of the scanner. Some scanners doesn't even have the chip and filters to do FM broadcast reception.

/Ubbe

 

[jonwienke]

In other scanners there's always a seperate IF discriminator chip connected before the FM and NFM filters that is handling the FM broadcast reception. In SDS100 it is a software defined receiver doing it all and it can be tricky to have a filter design that allow both narrow band 12,5KHz and WFM 150KHz using the same components.

The SDS100 is using software to determine channel width, not physical filters, the same as when using SDR# and a RTL dongle. The most likely cause of the problem is a firmware bug that manifests when the channel width is set wider than 25KHz.

 

[gschmitz]

Is priority activated?

 

[jonwienke]

No. That's why the problem doesn't happen on all channels.

 

[JamesO]

No Priority active.

I did not and will not have time to screw around and experiment much more this weekend with this issue.

Interesting it is not specifically a high signal level from what I can tell, it seems more to be station dependent. Not sure what sub carriers or HD digital data stream is with the specific station.

My initial thought is the IF bandwidth is too narrow because the fidelity and sound quality is not what it could and should be for Wideband FM Broadcast recovery.

Possibly there is something with the FM Broadcast band in the country where the firmware is being developed and there are differences from the US FM Broadcast band that might be part of the issue.

 

[CommLt]

I'm thinking it may not be the scanner. I have been noticing that on FM in my truck driving around town. May be problems with dynamic ad insertion on their end.

 

[kikito]

FWIW, I’ve been testing this also and seen what the OP mentions a few times already. I’ve also been noticing in some stations, the RSSI constantly fluctuating between -60 and -80 dBm.

 

[jasonhouk]

Monitor "Noise" when this happens. There could be a correlation.

Houk

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