[600MRG] Determining noise floor in my location

Sun Oct 21 12:54:47 EDT 2018

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 hams 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.  

See the attached image for an map of who was active the last 12 hours.

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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-----Original Message-----
From: michael polia via 600MRG <600mrg at mailman.qth.net>
To: 600mrg <600mrg at mailman.qth.net>
Sent: Sun, Oct 21, 2018 10:07 am
Subject: [600MRG] Determining noise floor in my location

I've been trying to determine the noise floor at my location for 630m. 

I am using a local AM station (WTAG) at 580 KHz as a reference. 

The contour map for this station claims a field strength of about 2.0 mV/m at my location with a published field strength of 141 mV/m at 1 Km along the contour plot azimuth between the station antenna and my QTH.

When I compare the relative received signal strength of this station against the received noise level, the difference is about 47 dB (measured using HDSDR program). 

If I am correctly calculating this, the noise floor at my QTH is 9 uV/m which seems too high for any meaningful reception of stations on 630m.

Any thoughts?

Thanks

73
Mike
AB1AW

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