The Importance of AGC on SDR Radios like the Xiegu G90

I've mentioned a couple of times earlier on that I've always had the G90 get hammered by a local HAM. He is, quite literally over the back fence about a block away. 

So the G90 lives in a shed, running off solar charged batteries. It's connected to a vertical on the end of a 50m run of LMR400. Normally I use it remotely for digital modes - the vertical tends to be a bit too noisy for much else.

I happened to be in the shed the other day and decided to have a listen around briefly and noted that my neighbour was on a net. As a rule, the radio has the AGC off - I tend to find that I receive a lot more FT8 that way so it's how the radio is normally set. I started tuning around with the audio set to a single bar, and when I hit 7.115 MHz, I was just about blasted out of the room. So I turned it down. And it was still pretty loud... with the attenuator on.

  

As you can see, even with the volume effectively "off", he's still completely audible. It doesn't sound "that loud" on the video, but in a quiet environment, it goes from comfortably loud to.. excessive with only a slight touch of the volume knob.  

I flicked on AGC to see how that improves things. I've never really given AGC a "good" test before, but this certainly illustrated the point.
 

That certainly makes a difference..

The SDRs certainly get overwhelmed a lot easier than non-SDR radios, and clearly the AGC function does a lot more than I'd ever given it credit for. 

Along the same lines, I was doing some FT4 and FT8 on 40m earlier this morning using the G90 in the shed and I could hear my transmissions at the desk. That was... alarming. I spent a few minutes chasing the source, before I realised that it was the Malachit SDR receiver on my desk. I'd plugged it in yesterday to charge (I can't access the power button in the case I printed), but I'd managed to turn off the screen. The volume was set low enough that I normally can't hear it.

It was set to just over 7.105MHz, connected to a bit of coax that connects to a switch in my study that the IC706 uses to connect to my dipole. Even with the switch set to the IC706, enough was still getting through to the Malachit to overload it - the waterfall lighting up like a Christmas tree. That switch won't be there much longer clearly. Cheap switches.. hmm. 

So, in all of that my learnings here are:

1) AGC actually works. I should probably use it. 

2) I was justified in loosing the other 3 of those coax switches. 

3) SDRs overload easily, which makes me wonder how effective it really is to rely on their waterfalls for telling how clean a really strong signal actually is.