[600MRG] Determining noise floor in my location

[Edward R Cole]

Steve,

Excellent advice.

One thing you can do is compare noise level with no station 
signal.  Connect 50-ohm load to receiver and note noise level on 
s-meter or better by observing a spectrum display using a program 
like Spectavue.  Spectravue will use digital output of most 
soundcards which you can connect speaker or headphone output from the 
receivver.  Spectravue has a display mode called "Continuum" which 
shows the spectrum amplitude directly in dBm vs time or vs frequency 
up to 190 KHz bandwidth.

Then connect receiver to antenna and compare noise display on 
Spectravue.  I get -130 dBm noise floor with my SDR-IQ connected to 
load and -115 to -105 dBm when connected to my inverted-L (43H by 
122L).  Obviously I am seeing a lot of local noise.

I can tune in BC stations with this system to compare signal 
level.  Local am station KSRM on 920 KHz about 15 miles from me runs 
at about -90 dBm.  Not sure what they output in power but they use a 
1/4-wave vertical.  I can hear stations from Anchorage 70 miles north 
as well.  They typically run 50-100kw so are almost as strong.  I 
have a RGPS station less than a km away on 310 KHz and it is -30 dBm 
(super strong).  An ADIS station on 395 KHz 12 miles away at our 
local airport runs about -60 dBm.

Short of using a calibrated signal generator that is about all one 
can do is view relative readings.  To do a proper MDS calculation one 
would have to insert a known level of RF into the antenna feedline to 
see actual SNR.  For commercial repeater servicing this is commonly 
done.  Bird power meters have an isolation slug which can be used to 
insert a signal (typically 50 dB coupling).

73, Ed - KL7UW

At 08:57 AM 10/21/2018, Steve WD8DAS via 600MRG 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>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>http://www.wd8das.net/Tracking-Radio-Noise.pdf
>
>
>Steve WD8DAS
>
><mailto:sbjohnston at aol.com>sbjohnston at aol.com
>http://www.wd8das.net/
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com 
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