SDS100/SDS200: SDS100 very noisy while driving, but other HT is fine

[IcomIcR20]

Hello all,

I have been doing some testing the past few days after discovering something odd. My SDS100 suffers from very bad interference on VHF/UHF (800 MHz seems ok) while my vehicle is in motion. At first, I was thinking my car was likely the culprit, so I began testing with a mag mount on the roof as far away from the engine as possible. The noise is still present on my SDS100, but when I hooked up an Icom HT to the exact same antenna, the interference issues were no longer present. Both radios were running on battery power. Both radios were tested by driving around the same area.

The best way I can describe the interference is rapid variations in the noise floor causing normally reasonably strong transmissions to become very noisy and often cut in and out. Here is an example: SDS100 interference

This does not happen when the vehicle is stationary or when using the SDS at home.

Any ideas as to why this happens on my SDS, but not my Icom?

 

[JoeBearcat]

Is the Icom SDR-based? If not, apples and oranges.

Try the various filters. There are RR threads that talk about what each does.

 

[IcomIcR20]

Is the Icom SDR-based? If not, apples and oranges.

Try the various filters. There are RR threads that talk about what each does.

It is not... it is an older IC-R20. I will have to try messing around with the filters some. It is just odd to me that the SDS can suffer so badly while the Icom is unaffected.

 

[RFI-EMI-GUY]

If I had to guess, the SDR lacks an effective Limiter circuit before the FM detector:

A Limiter circuit is used in FM receiver to remove the noise present in the peaks of the received signal and to remove any amplitude variation in the received signal; the output of the limiter has constant amplitude.

 

[tvengr]

and often cut in and out.

Check your squelch setting. It should be 2.

 

[IcomIcR20]

Check your squelch setting. It should be 2.

That is the first thing I checked. It is indeed set at 2

 

[Ubbe]

SDS100 has a I/Q detector and are DSP based. Try change from NFM to FM and also test IFX and of course the many different filter settings.
But as mentioned the SDS100 use a SDR receiver very much like those in a $10 dongle and doesn't have the same quality in reception as conventional receivers like a R20. There's a reson to why SDS scanners has all those filter settings and while your R20 doesn't need them.

/Ubbe

 

[gmclam]

You say noise so I guess you are listening to analog? When I am just in town I include scanning of CHP on my SDS-100. They are analog FM on VHF low band. Unless an extremely strong signal, it is noisy. Everything else I monitor in the county is P25. I figured out that the noise is coming from the USB power adapter I am powering the SDS from. Unplug the power cable and the noise is gone.

This is likely a noisy switcher in the USB power adapter but I expect the SDS to have better PSRR than it does.

 

[IcomIcR20]

SDS100 has a I/Q detector and are DSP based. Try change from NFM to FM and also test IFX and of course the many different filter settings.
But as mentioned the SDS100 use a SDR receiver very much like those in a $10 dongle and doesn't have the same quality in reception as conventional receivers like a R20. There's a reson to why SDS scanners has all those filter settings and while your R20 doesn't need them.

/Ubbe

Thank you sir! That is a very reasonable explanation and definitely makes sense. I guess I expected more from a flagship Uniden scanner as compared to an older communications receiver in terms of its ability to reject interference. I suppose I will use the Uniden on 800 MHz systems and the Icom for VHF/UHF while mobile.