[hpsdr] NOISE FLOOR

[Tony Hagen]

Thank you all – its now clear – thank you very much

73
Tony

From: Scott Traurig 
Sent: Thursday, January 17, 2019 6:50 PM
To: Helmut Oeller 
Cc: Tony Hagen ; hpsdr 
Subject: Re: [hpsdr] NOISE FLOOR

Tony, 

Common rule of thumb: attenuator noise figure = attenuation. When the attenuator comes before the first amplifier, as it does in most radios, its noise figure will dominate the noise figure cascade analysis.

You can easily demonstrate this by first applying enough attenuation to see the noise floor rise a little (you have to make noise figure bad enough so it becomes a factor). Then increase the attenuator by 10dB and you will see the noise floor jump up approx. 10dB.

See here for more on noise figure and noise figure cascade analysis. There is a link there to a handy calculator that works a three stage Friis equation:

https://www.microwaves101.com/encyclopedias/noise-figure


The preamp (the only amp!) gain in the 7000 and 8000 is 14dB. In the other radios it is 20dB. In all cases the preamp noise figure is about 6dB.

Lots of GREAT stuff at the Microwaves101 site, BTW.

Also somewhat related:

https://apache-labs.com/community/viewtopic.php?f=6&t=2463


73,

Scott/w-u-2-o


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