Noise Floor

  • 1
  • Question
  • Updated 5 years ago
  • Answered
I live in a residential neighborhood and find that the noise floor on 20 meters using a three element SteppIR beam is around -110. RF gain is at zero. I am wondering what others have experienced based on where you live.
Photo of Richard, N7HX

Richard, N7HX

  • 30 Posts
  • 3 Reply Likes

Posted 5 years ago

  • 1
Photo of Sergey, R5AU

Sergey, R5AU

  • 801 Posts
  • 96 Reply Likes
Hi Richard,
noise floor depends on the bandwith of the reciever

you can see more with details regarding F6000 on:
http://community.flexradio.com/flexra...
Photo of Tim K8XS

Tim K8XS

  • 48 Posts
  • 8 Reply Likes
Richard,
Good question; however, Sergey is correct. You will notice that as you decrease the span you are looking at, the noise floor goes down. Unfortunately, I have no idea how to know the FFT size or equivalent bandwidth SSDR is using. I also don't know how to set our displays so that the bandwidths are equal. We can come close; but, not exact. Approximately how much bandwidth is displayed when you see the -110 dBm noise floor?
Photo of Richard, N7HX

Richard, N7HX

  • 30 Posts
  • 3 Reply Likes
I am now looking at the whole 20 meter extra phone band, 14.150 to 14.350 and my noise floor is reading -110. I have my SteppIR beam tuned to 14.250.
Photo of George Molnar, KF2T

George Molnar, KF2T, Elmer

  • 1529 Posts
  • 541 Reply Likes
Echoing the other comments - "it depends." Here, on 20m with the panadapter zoomed in as far as it can go (1 kHz markings, 0.5 kHz graticule), I'm getting about minus 125-130 in my suburban neighborhood featuring buried utilities.

Just clicking on the band and getting the default zoom (10 kHz markings, 5 kHz graticule), I'm reading about -115.

When I first started with the rig, I was seeing about -115 zoomed in; it took a lot of work and substantial study to learn ways of effectively mitigating noise in the shack and house. It was very worth it!

So, I'd say that an indicated -110 on 20 meters "probably" represents room for improvement.
Photo of Dave - WB5NHL

Dave - WB5NHL

  • 266 Posts
  • 60 Reply Likes
Here is what Steve (N5AC) VP Engineering had to say about noise floor

......Both the panadapter and the meter in a slice receiver show the noise floor level when a signal is not present in a bin or passband, respectively. In the case of the panadapter, the bin size changes with zoom level and so the noise floor will consequently change. For example, if your pandapter is zoomed in to say 15kHz wide, your bin size is 5.86Hz per bin. If you zoom out to 30kHz, you are now looking at a bin size of 11.72Hz. Since there is twice the bandwidth, there will be twice the noise in the bin and the noise floor will rise by 3dB.

On the other hand, the receiver noise bandwidth is set by the filter in the slice receiver. So if you set it for 500Hz, your noise level is much higher than is in the panadapter bin which is being measured at only 5.86Hz (almost 20dB difference).

Another way to see this is to set your bandwidth in the slice receiver to 500Hz and then hover over the S-meter. Where I am, I get a noise floor reading of -121dBm on 20m. I then expand the filter to 2.5kHz and I read -114dBm. The calculated difference is 10*log(2500 / 500) = 6.99dB and of course -121dBm + 6.99dB = -114dBm. Then if I go down to 50Hz bandwidth in my receiver filter, I read -131dBm. The calculated value is 10*log(500/50) = 10dB better or -121 -10 = -131dBm. This is how noise measurement works and why you have to specify the bandwidth where you are measuring the noise.

Finally, if you are connected to an antenna, your noise floor will change (of course) based on the antenna type, the noise level and type at your location, etc.

Steve