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

[EricRF]

Hi all... a beginner here craving knowledge and enlightenment. But I'll settle for some assistance.

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, "thrumming" seems more accurate) on certain channels. The sound is on top of (or behind?) the audio on the channel.
Conventional analog digital channels are OK
Trunk channels (at least the ones with any traffic) have the problem. I don't hear it through the speaker, just headphones, and only on trunked systems. And I believe this system is simucast.

Here's a sample channel:
Massachusetts State Police (Trunk)

Metro Boston Simucast (Site)​

State Police Troop A - North Greater Boston (Talkgroup)​

North Dispatch - A, A1, A2, A3, A6 (Channel)​

(I think I have the terminology right)

I can hear the audio OK, but the thrumming makes my brain dissolve. I can't hear any sign of it through the speaker. And, again, no sign of it on conventional analog or digital channels.

Any ideas?

Thanks!

 

[KevinC]

I’d vote for it’s the LSD (Low Speed Data) and your headphones have a much better frequency response than the internal speaker.

 

[nd5y]

That looks like a Type II analog system. On analog voice channels there is a low speed "subaudible" data stream similar to DCS (Digital Code Squelch) or the data stream used in LTR trunking.

If it is an analog simulcast system there could also be an effect from the multiple transmitters that can sound like that depending on your location in relation to the transmitters.

You are probably hearing one or more of the above.

 

[EricRF]

Thanks for your replies... Yep, it's labelled as a Motorola Type II SmartZone system. Are analog simucast systems prone to this problem on the SDS100?

So far we have:

• Cheap $10 headphones with a better frequency response than the SDS100 speaker
• LSD (which immediately made me think of the '60s)
• Simucast side-effects
• "Data stream" reminds me of of Star Trek transporters. Now if pattern buffers are also involved...

I assume no transporters are in use, so are there any settings I can tweak which might help? I'm completely out of my depth, so even though I understand the possible causes, I have no idea of things to try to solve the problem.

One other data point... There are two sites for that system that cover my area. They're both in the favorites list under Massachusetts State Police, mentioned previously, and Boston. I tried avoiding one and the other, but that doesn't seem to help. Don't know if that's important, but I thought I'd mention it.

Any thought?

 

[KevinC]

Whether it’s LSD or phase noise you can’t fix that. Either wait for your hearing to get worse or find some headphones with less bass response.

 

[wtp]

when my county was on 800 analog and simulcast, i could hear a low hum to a squeaky wheel sound.
they are now on 700 and digital, no hum but i have problems receiving them.
try going getting closer to a tower. that seemed to help.

 

[EricRF]

Thanks for your help...

Whether it’s LSD or phase noise you can’t fix that. Either wait for your hearing to get worse or find some headphones with less bass response.

Aw, nuts. I might have to use a tin can and string for a headphone.

when my county was on 800 analog and simulcast, i could hear a low hum to a squeaky wheel sound.
they are now on 700 and digital, no hum but i have problems receiving them.
try going getting closer to a tower. that seemed to help.

I can try that, just to see, but I listen mostly at home, so not a long-term solution.

Is the SDS100 known for issues with analog simucast systems, or can this happen on any rig?

 

[wtp]

you could start small and just walk around outside the house to see any difference.
the house will help in blocking out other towers.

 

[EricRF]

you could start small and just walk around outside the house to see any difference.
the house will help in blocking out other towers.

I'll give that a shot to start, at least. Thanks!

 

[EricRF]

Taking an earlier suggestion to heart (thanks @KevinC) , I'm trying to find headphones with poor base response. You don't see to many advertised with that "feature". My current set, $12, claims freq resp of 12-24,000Hz. I just order another set for $5 which claims response of 80-18,000hz. Hope that does the trick! At least they're not expensive.

 

[wtp]

another thought is to use it without headphones...

 

[EricRF]

another thought is to use it without headphones...

I got the headphones because I had a hard time understanding the audio from the little speaker on the SDS100 (and so I can listen without disturbing the rest of the household). If I can't find a way to use headphones without the thrumming, then I'll have to do without.☹️

It's kind of a bummer though.

 

[RandyKuff]

I've been using these headphones with my 100... And don't get any motorboating sound or what ever your hearing...
But they don't make them anymore... And anybody that has them is price gouging...
I only paid like $12 for them brand new from Best Buy several years ago...

 

[KevinC]

I've been using these headphones with my 100... And don't get any motorboating sound or what ever your hearing...
But they don't make them anymore... And anybody that has them is price gouging...
I only paid like $12 for them brand new from Best Buy several years ago...

View attachment 127579

Are you listening to a simulcast 3600 Motorola system?

 

[RandyKuff]

Marcs IP Statewide System, But my site/tower is not simulcast in Lorain County, Ohio...

 

[KevinC]

Marcs IP, But my site/tower is not simulcast...

Ok. That’s 9600 so no LSD.

 

[RandyKuff]

You think LSD might be causing that?

 

[KevinC]

You think LSD might be causing that?

Either that or phase noise from the simulcast.

 

[RandyKuff]

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

 

[wtp]

you would have to get to a 'bad spot' to check it.