Icom R75's noise reduction feature

[GB46]

Something I've noticed while using R75's noise reduction feature:

When I'm decoding FT8 with WSJT-X, the spectrum display, which I've set to start at 0 hz, always shows a spike at slightly above 50 hz. This doesn't disappear or change in any way between passes. Now, if I activate the noise reduction function, the spike increases significantly in amplitude. The higher the NR level, the higher the spike. At first I thought it was from 60 hz AC hum, but none of that is in the least bit audible.

According to Icom, NR suppresses the noise, while extracting the signal and resampling it. I don't know beans about how DSP is supposed to achieve that, but something tells me that the spike is being introduced by it. It doesn't impair decoding of the signals, as their frequencies are much higher, but I'm just curious about what's going on. Ideas, anyone?

Not that the noise reduction is much help. It's not very effective In AM mode, although some sideband signals benefit from it. NR kind of smooths out the noise, but either lowers the volume of the signal or distorts it, depending on the level chosen, so if I use it at all I generally don't exceed the level of 3.

 

[mbott]

Gerry,
I don't have an answer to your question, but I've always been impressed with the R75's ability to deal with noise. My R75 arrived without the UT-106 DSP which I ordered from DX Engineering prior to the R75s arrival. This one does have the AM Synch so it was a no brainer to send it on to Kiwa Electronics for their synch fix. I live in a noise rich environment, so anything I can do to reduce the impact of that noise makes the hobby more enjoyable for me.

 

[GB46]

I live in a noise rich environment, so anything I can do to reduce the impact of that noise makes the hobby more enjoyable for me.

My environment is noise rich, too, but signal poor at the same time, which is bad news for HF.

As for the noise level, I get far less of it using my portable with just the whip. If there's something to be heard, I'll hear it. Signals are slightly weaker, of course, but much easier to listen to. The problem is that the R75 requires an external antenna, which is efficient at bringing in RFI from all directions. Twin passband tuning is the only feature of the radio that helps me cut the noise down a bit. It helps on SSB, but isn't very effective on AM unless I use a really narrow filter. That makes the audio too muffled, however.

My R75 has AM sync, too, but it's ineffective, and I've never wanted to send the receiver out for modifications. It didn't come with the DSP module, which I bought and installed in 2003, a full 5 years after buying the radio.