User Option to Rescale Display on Zoom

KY6LA_Howard

It can be annoying to have to readjust the display so that the noise floor is at the bottom rather than the middle of the display when zooming out and becomes hidden below the bottom of the display when zooming in… Feature Request… User Option to rescale on Zoom so that you do not need to constantly readjust the baseline

Steve-N5AC

We discussed this at length when we did the panadapter, Howard. We talked about trying to have a single level in the display where we would set the noise floor so you could set that position and then as you zoomed in/out or switched bands, the floor would be in the same place. But we found some issues with this approach: 1. As you zoom in, you are able to see further into the noise in the panadapter. This is called "processing gain" and it works like this -- when we reduce the size of an FFT bin, say from 20 to 10Hz, there will be half the noise in the bin. So the noise floor goes down by this amount. Today, if you zoom in, a signal stays at the same level in the display and the noise floor drops. If we keep the level constant in the display when this happens, the signal will rise in the display! We debated about which of these was better/worse and the answer didn't seem clear. 2. We were unsure of how to measure the noise floor and for how long to set this. For example, if you switched the zoom right as an adjacent station at field day was spraying phase noise in the band with his transmitter, your noise floor would be set by this. When he unkeyed, your floor would again be below the display. So the question became -- how long do we look at the noise floor to decide where it "really" is? 3. If you switched physical antennas without changing anything in SmartSDR, the noise floor is likely to change. Do we look at this and change based on this as well? If so, how often and for how long do we look to determine where the noise floor is? I suppose we could use a very long running filter with second(s) of delay that works a little like an AGC to move the noise floor to a set level. Then short duration events wouldn't move it, but more permanent ones would. We could accelerate the time constant when you are zooming. Well I don't know, perhaps I just talked myself into doing it like this. I'd like to hear other opinions. Steve

Al K0VM

It seems to me that the change in noise floor with panadapter width is a fixed constant... Double the spectrum display span and the noise in each bin is doubled. Thus it should be possible for the user to adjust and save the scaling for each band and a display width factor be applied from there.. Obviously i'ts not automatic if the noise environment changes or a different antenna is selected. AL, K0VM

Bill - K7UOP

I wrote a program for my F5K to plot signal levels vs time (chart recorder) including SNR (really great to have lab quality levels - dBm . I started with just a manual Reset Noise Floor button. I added auto reset upon mode, filter or band changes. Maybe in this case, on a panadapter, when a user sets the noise floor to a particular location, subsequent changes likely to effect noise would re-adjust it to the set location on the display.

Steve-N5AC

Correct. So does this mean that you prefer the noise floor to stay constant and have the signal level move up and down rather than signal level stay constant and noise floor move up and down? Steve

Al K0VM

Yes, With out seeing it in action, I think I would rather have the noise floor in a fixed spot and let the real signals move, as long as the right db scal also moves... but I could be wrong and no like that AL, K0VM

Al_NN4ZZ

Also agree. If you want to offer both options, I'd call the constant noise floor feature the decaf option. Regards, Al / NN4ZZ

KY6LA_Howard

Right now when I change bandwidth, i have to mouse over and change the scale so that they noise floor stays as the bottom of the screen Personally I want to the noise floor to stay at the same physical location on the screen and the scale to move up or down as you decrease or increase the bandwidth.

Ken - NM9P

It would be nice if it would automatically reposition itself, but not be locked to that spot. I love being able to slide it up or down depending upon the zoom level of the right hand scale in order to make sure I don't miss any details. Another Suggestion: Rather than having the zoom-up and zoom-down buttons on the RH side of the display scale, perhaps you could use left-mouse drag for repositioning the baseline, as it is now, and use a right-mouse drag in order to zoom-in and zoom out the scale in the same way the bottom scale is zoomed or panned. When right-mouse dragging the scale, the baseline would stay the same and the top of the scale would move up & down. This seems more intuitive to me than trying to remember which button does what. ( I seem to hit the wrong one first about 50% of the time.)