SDS100 - a few oddities...

[nessnet]

I have noticed a couple of quirks on my SDS100.

First
I'd have to put it on a scope to determine the freq. When connected to an external speaker, the audio out, (during a transmission), has a pronounced low frequency 'rumble'. It's fairly low, maybe 30-40Hz, possibly lower?

Does everyone also have it? Does someone have a scope handy they can hook up and determine the freq? I applied multiple notch filters in ProScan, but when in the car, I hook it into the aux input of the car sound system and it really comes through. I suppose I'm going to have to build a filter for the car as well.

Second
My radar detector (V1) was alerting periodically on X band. I figured out that it was doing it when the SDS100 was scanning VHF - looked like 167.XX or 168.XX. Definitely VHF in and around 165-170. It's not putting out any other interference on any other band, at least none that sets off the V1.

 

[nessnet]

Update:

This may be an artifact of a system. IE: I don't seem to hear the "rumble" on a P25 system I monitor.

The system that seems to have this issue is KCERS (King Co Public Safety). I'll have to do some driving around to see if other systems have this issue.

 

[jonwienke]

When connected to an external speaker, the audio out, (during a transmission), has a pronounced low frequency 'rumble'. It's fairly low, maybe 30-40Hz, possibly lower?

You're hearing the CTCSS tone. It's not being filtered out. You'll only hear it on some analog channels, but not on digital channels. Audio should have a 280Hz high-pass filter on analog channels, and a 100Hz high-pass filter on digital channels.

 

[nessnet]

Hi Jon,

Yea, I'm hearing it on different systems (analog) as well.
Makes sense that it is CTCSS tone.

"Should".... Paul, you seeing this??

 

[Ubbe]

It's difficult to make a filter that removes all resudials of a subtone frequency. The small speaker in a scanner cannot reproduce the rest of the low frequency signal but a wider range external speaker will. It is also not unusual that the subtone frequency are not completly 100% pure, either from the transmitter source or from low resolution digital audio processing in the receiver, and have some artifacts that generates products higher up in frequency above the filters range.

A very effective filter would be a auto notch filter and not a fixed hight pass filter. I have it in my Icom receiver and it works really well. It's probably too expensive for a conventional scanner but a SDR application like the SDS100 would have no problem implementing this, just adding a one time cost for the work hours from the firmware coder guy.

/Ubbe

 

[jonwienke]

It's difficult to make a filter that removes all resudials of a subtone frequency.

No it isn't. Especially in software. Digital audio editor programs have been doing it for decades. And so do SDR programs like SDR#. In the audio range, there are many consumer-level software packages that can do high-pass and low-pass filters with pretty much complete cutoff within 1-2% of the set frequency.

 

[nessnet]

Of note here: my 436, in the same setup, didn't have this audio (low freq CTCSS rumble on analog) issue.

I was hoping that this is possibly going to be addressed via firmware...?

Paul??
(should this be reported as a 'bug'?)

 

[jonwienke]

Of note here: my 436, in the same setup, didn't have this audio (low freq CTCSS rumble on analog) issue.

I was hoping that this is possibly going to be addressed via firmware...?

Paul??
(should this be reported as a 'bug'?)

The 436 filters out CTCSS tones below 100Hz, but you can still hear CTCSS tones above 100Hz.

 

[nessnet]

I thought about this some more.

Jon, the system I'm hearing this "rumble' on is a Motorola Type II SmartZone.
Seattle-King County Public Safety (KCERS) Trunking System, Seattle, Washington - Scanner Frequencies
It doesn't(??) use CTCSS tones.

I do see up top of the system's RR page a "connect tone" of 83.72.

Another system I'm hearing it on:
Snohomish County Public Safety (SERS) Trunking System, Everett, Washington - Scanner Frequencies
Also Motorola Type II SmartZone
"Connect tone" of: 97.3

 

[jonwienke]

The connect tone is the same sort of thing as CTCSS, just in a trunked system instead of a standalone analog frequency.

All of this gets solved if the scanner applies a 260Hz high-pass filter on analog transmissions (except WFM and FMB), and 100Hz high-pass filter on digital transmissions. FMB and WFM should have a high-pass filter of 20Hz.

WFM and FMB should have a 15-20KHz low-pass filter, everything else should have a 3-5KHz low-pass filter.

 

[MAguln8839]

I am hoping this will be addressed soon. Using an external speaker, the tones are very noticeable. The internal speaker does not have a low frequency response and the tones cannot be heard, but very annoying when a better speaker is used with a fuller frequency response.

 

[nessnet]

Paul (UPMan) I do hope you are reading this...?
(I e-mailed him a link to this thread)

 

[Ubbe]

Motorolas Smartzone Smartnet Startsite systems uses a low speed datasignal on the voice channels, it sounds similar as a DCS subtone around 170Hz.

If it is as Jon says that digital channels in a scanner only filters out audio up to 100Hz then the 170Hz will pass through, if a smartzone system have been thought by mistake to be digital in the scanner as it is a trunked system. A typical bug in a new scanner that might not have taken in all knowledge learnt from previous scanners, new folks doing the firmware.

/Ubbe