ARRL

Secure Site Login

Forum Home - Rules - Help - Login - Forgot Password
Members can access, post and reply to the forums below. Before you do, please first read the RULES.

how can you measure the rx noise floor at your qth

Jun 10th 2017, 11:06

KK4BHS

Joined: Apr 15th 2011, 16:46
Total Topics: 0
Total Posts: 0
I was watching an online video and the presenter was talking about the dbm of the noise floor at his location and the difference in noise floors in dbm from location to location be it urban or rural and if local am radio stations were in the area etcetc. What I am wanting to know is how does one measure that number he was giving?
Where did he get the dbm of the noise floor of his location? How can I measure mine?
Im looking at ways to eliminate or lower interference and noise that I may have control over. Any help is much appreciated. Still new to learning and need a lot of help LOL
Jun 10th 2017, 15:25

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
In theory, it is just a matter of looking at a panadapter display that goes down to -130 dBm or so with a 2 kHz bandwidth. In theory, the thermal noise limit is -174 dB/Hz so with a 2kHz bandwidth the maximum sensitivity of a receiver with that bandwidth is -140 dBm. Most people are very good at picking out various signals and ignoring them when making an estimate of the noise floor--it may be a little tougher to program an automatic system to make that distinction. It is very easy to introduce common mode noise generated in the ham shack while making his measurement. Tom, W8JI has some suggestions on this web page.
https://www.w8ji.com/noise.htm

Zack Lau W1VT
ARRL Senior Lab Engineer
Jun 11th 2017, 13:54

KK4BHS

Joined: Apr 15th 2011, 16:46
Total Topics: 0
Total Posts: 0
thanks for the info will check out the site
Jun 12th 2017, 21:09

ralphm

Joined: Jul 15th 2016, 22:48
Total Topics: 0
Total Posts: 0
To put this noise floor stuff into perspective, -140dBm in a 50 ohm system is 0.022uV. I think even the best receivers have a sensitivity of about 0.25uV for 10dB S+N/N for < 2kHz bandwidth. RF amps, mixers, and IF amps and detector all add noise.

Back to Top