SDS100/SDS200: Hum while receiving analog comms

[tumegpc]

I noticed that the SDS100 has a hum sometimes while receiving analog communications. It sounds like an amp that has a bad ground. This is not present on the 436HP, TRX-1 or the 325P2.

 

[RFI-EMI-GUY]

I noticed that the SDS100 has a hum sometimes while receiving analog communications. It sounds like an amp that has a bad ground. This is not present on the 436HP, TRX-1 or the 325P2.

See if you hear it listening to a weather channel. If not, it is CTCSS tone bleeding in. There normally should be a high pass filter in the radio to cut out tones below 200Hz.

If you hear it on a WX channel, are you using a charger and/or external antenna when receiving?

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[jonwienke]

The SDS100 filters out DCS and CTCSS tones below 100Hz, but you can still hear the higher ones if listening with a speaker or headphones with decent bass response.

 

[tumegpc]

See if you hear it listening to a weather channel. If not, it is CTCSS tone bleeding in. There normally should be a high pass filter in the radio to cut out tones below 200Hz.

If you hear it on a WX channel, are you using a charger and/or external antenna when receiving?

Not hearing it on a weather channel , and no charger with stock antenna. I will record audio files from the 436HP and SDS100 and upload them when I get a chance.

 

[RFI-EMI-GUY]

100 Hz cutoff sounds a bit marginal. 200 Hz would be more like it. This article compares performance of some various commercial radios.

http://www.scomcontrollers.com/downloads/ctcsssreject&hpfilters.pdf



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[jonwienke]

100Hz high-pass is reasonable for digital (P25, DMR, NXDN, etc), but for analog it should be about 270Hz to eliminate all of the CTCSS tones.