[600MRG] Determining noise floor in my location

[michael polia]

 Hey guys!
Thank you for your feedback.
Equipment here is a Cross Country Wireless SDR 4+ LF receiver (2 KHz to 2.5 Mhz) w/ LF Engineering L400B active antenna (powered by linear power supply). 
With the exception of raising the antenna height by 6 feet, this is the same equipment I was successfully using last winter and was able to receive and post WSPR reports from stations up and down the east coast, Midwest and Caribbean. 
Not sure what is different this year except for being more rainy and wetter than usual. 
I do turn off the PC monitor and unplug all the wall-warts in my shack (home office).
 I did connect my receiver to antenna and compare noise display against 50 ohm load.  I get -125 dBm noise floor with my SDR-IQ connected to a 50 ohm  load and -80 to -75dBm when connected to my active antenna.

Looks like I need to go RFI hunting.
73MikeAB1AW


    On Sunday, October 21, 2018, 12:57:33 PM EDT, Steve WD8DAS via 600MRG <600mrg at mailman.qth.net> wrote:  
 
 
There are a lot of uncontrolled variables in your calculations.  For example, the actual signal level of the broadcast station could easily be different from the predicted field strength at your location.  Maybe the station is not running at licensed power.  Maybe the ground conductivity today between you and the station is not what was shown on the FCC chart from many decades ago.  Maybe their antenna system has lost performance, or is operating at variance from the licensed parameters.  Maybe increased urbanization between you and the station has increased the "path loss".  What about the bandwidth?  What about...  And so on...  

I think you are on the right track with the idea of relative comparison of known signals to noise, but I think it would only be meaningful when comparing one reception situation to another.  For example, you could use ratios of broadcast signal to noise to show that reception at your house is more troubled by noise than at a nearby ham's house.
I've found it very difficult to put numbers on noise, but what really matters is practical experience.  When you tune a receiver to 630 meters (one that is known to actually work below the broadcast band) do you hear any stations?  Try an HF antenna - one of my best receive antennas is a 75m inverted vee.  There are quite a few stations active, mostly using the digital modes like WSPR and JT9.  My WSPR station transmits every few minutes, for example.  You can visit http://wsprnet.org/drupal/wsprnet/map anytime to see who is running WSPR.  

It is certainly possible you have a high noise level.  What have you done to minimize noise coming from your own home?   This will improve your experience on HF/VHF/UHF as well as MF.   

Here's a link to a presentation I made on the subject of tracking noise.  It is oriented toward broadcasters but applies to any users of radio.  I used a comparison of the relative noise to show how many locations have more indoor noise than outdoors at the same address.  it also shows tips for finding noise sources.

http://www.wd8das.net/Tracking-Radio-Noise.pdf
 
Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
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