Noise figure Q - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews

-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

James
Post subject: Noise figure Q.
Unread postPosted: Thu May 13, 2004 6:55 pm

If a filter has 1dB IL at ambient, the noise figure is 1dB. If at hot temperature, the filter has 1.5dB IL, will the NF be higher than 1.5dB?

Top

Guest
Post subject: Noise Figure will remain 1.5
Unread postPosted: Fri May 14, 2004 6:57 am

At higher temperature the overall noise power floor will be higher (KTB). However, noise figure is the ratio between the signal to noise ratio at the output to the signal to noise ratio at the input therefore the noise floor is cancelled out and what is left is the additive noise from the filter, or what you know as noise figure. In this case the additive noise is 1.5dB, which is the noise figure.

Top

Itay
Post subject: Correction to the formula
Unread postPosted: Fri May 14, 2004 10:48 am

Correction to the ratio you provided, the noise figure is the ratio between the S/N in the input to the one in the output.

Thanks,

Itay Reiss

Top

Tony Kurlovich
Post subject: Consider
Unread postPosted: Tue May 18, 2004 11:38 am

When NF is tested over temprature, is the ENR source in the chamber? Most people have it out side the chamber and NF is calculated based on an ambient reference temp.

Posted 11/12/2012

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website: AirplanesAndRockets.com

My Daughter's Website: EquineKingdom

dB Control dB-9006 Magnum Opus Synthesizer - RF Cafe