SDS100/SDS200: Motorboating, Thrumming, ummmmm...

[KevinC]

I'll have to take mine into Cleveland (Simulcast) the next time I go and see what it sounds like with headphones...

If Cleveland isn’t 3600 you won’t have either LSD or phase noise.

 

[RandyKuff]

Well allrighty then...

 

[EricRF]

Hmmmm... hope you don't have a... bad LSD trip!!! 🤣🤣🤣🤣🤣🤣🤣🤣

 

[Ubbe]

When I put a set of headphones on my ears (connected to my SDS100), I'm hearing what I've seen called "thrumming" or "motorboating" sound (to me

When I had a SmartZone system in my area I heard the low speed data on the voice channels on every scanner I had. It sounded like "chugga-chugga-chugga" and when the call ended it sent an end tone "Brrrrrr".

Some scanners has a high pass audio filter at 250Hz to suppress any sub tones but it seems that some overtones from the LSD are still heard. SDS scanners, and perhaps others, disable the high pass filter during digital calls and it could be some issues or a bug when you have digital talk groups mixed with analog in your system if you only hear the LSD signaling in some of the calls.

/Ubbe

 

[EricRF]

Some scanners has a high pass audio filter at 250Hz to suppress any sub tones but it seems that some overtones from the LSD are still heard. SDS scanners, and perhaps others, disable the high pass filter during digital calls and it could be some issues or a bug when you have digital talk groups mixed with analog in your system if you only hear the LSD signaling in some of the calls.

Thanks Ubbe...
I'm hearing the noise on all calls on this one simucast trunk system. But it's also the only simucast trunk system I'm monitoring. Maybe I'll try to find another one...

The irony remains that I only hear it when I use headphones, which I do so I can hear the calls more clearly. I'd actually thought about putting a high-pass audio filter between the SDS100 and headphones. But I have no idea how to do that, and how expensive/difficult that would be. After spending that much money on the SDS100 I really had hoped not to run into problems of this sort. I guess I should have known better!

 

[wtp]

there could be a weird RF pick-up from the ground wire on the headphone.
humans ae also called 'stray capacitance to ground'.
i would say try computer speakers, but the same thing might happen, you could still try it though.

 

[EricRF]

there could be a weird RF pick-up from the ground wire on the headphone.
humans ae also called 'stray capacitance to ground'.
i would say try computer speakers, but the same thing might happen, you could still try it though.

Foolish humans!
I'll give it a try.
I have another pair of headphones on order. I know, just tossing money away. Very high-end. $5.00. We'll see if they make a difference as well.

Thanks!

 

[EricRF]

Just to update... My much cheaper $5 headphones, with a low-end frequency response of 80Hz arrived. And they help a lot. If I didn't know that the thrumming was there, I probably wouldn't notice it at all. It certainly isn't turning my brain to mush as quickly 🤪. I haven't had a chance to wander around much to see if it's a location issue.

 

[EricRF]

In my quest to find another Motorola Type II Smartzone system, like the one I'm having issues with, I'm finding systems called "Motorola Type II" and "Motorola Type II Smartnet" as well as "Motorola Type II Smartzone".

Are all those the same thing (WRT the issue I'm having?)

 

[nd5y]

Are all those the same thing (WRT the issue I'm having?)

Yes.

 

[nd5y]

Is this noise you are hearing a constant pattern that changes about 1/2 second before the voice channel transmission stops?

 

[EricRF]

Is this noise you are hearing a constant pattern that changes about 1/2 second before the voice channel transmission stops?

No, it's constant throughout the transmission.

 

[KevinC]

Just to update... My much cheaper $5 headphones, with a low-end frequency response of 80Hz arrived. And they help a lot. If I didn't know that the thrumming was there, I probably wouldn't notice it at all. It certainly isn't turning my brain to mush as quickly 🤪. I haven't had a chance to wander around much to see if it's a location issue.

Yea! I got something right again.

 

[EricRF]

So, basically, Low Speed Data is evil and must be destroyed? 🤪

 

[KevinC]

So, basically, Low Speed Data is evil and must be destroyed? 🤪

It could still be phase noise.

 

[nd5y]

So, basically, Low Speed Data is evil and must be destroyed? 🤪

Real radios are designed to filter out audio frequencies below 300 Hz so you can't hear low speed data, and other low level low frequency stuff like DCS or PL tones. Scanner manufacturers never did that.