Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes USAF radar shop Notable Quotes App Notes Calculators Education Engineering Magazines Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Stencils for Visio RF & EE Shapes for Word Advertising RF Cafe Homepage Sudoku puzzles Thank you for visiting RF Cafe!
Innovative Power Products Couplers

Noise floor - 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

Koos
 Post subject: Noise floor
Posted: Wed Sep 30, 2009 2:31 am 
 
Captain

Joined: Wed Sep 30, 2009 2:26 am
Posts: 6
I am transmitting carriers on one pol of a circular polarized antenna 9.3m Andrew. I wanted to use the other pol for more traffic, but as soon as the amp starts transmitting the noise floor of the opposit pol increases about 3db. How can I fix this problem? I do have a receive reject filter installed on the transmit.


 
   
 
nubbage
 Post subject: Re: Noise floor
Posted: Wed Sep 30, 2009 3:03 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 236
Location: London UK
Hi koos
I would suspect a mechanism in the ortho-mode transducer (OMT) that exhibits a combination of a slightly elevated VSWR and some mode/polarization conversion. In addition, the currents flowing on the dish surface will contribute to some of the increased noise level on the opposite polarization, as will backscatter from the sub-reflector (I imagine there is one).
If you analyze the expected levels on the degraded channel, from knowing a set of parameters such as return loss, CP Isolation and the channel bandpass filter characteristics, in terms of dBc, you may be able to see what deterioration in any of those would lead to the increase in noise floor you are seeing. One of the elements may be of particularly high sensitivity, so a very small departure from ideal will change the unwanted noise significantly. Only then can you address the issue of what to do about it.

_________________
At bottom, life is all about
Sucking in and blowing out.





Posted  11/12/2012
Windfreak Technologies withwave microwave devices - RF Cafe
Exodus Advanced Communications - RF Cafe LadyBug Technologies LB479A RF Power Sensor - RF Cafe
About RF Cafe
Kirt Blattenberger - RF Cafe Webmaster
Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,
    BSEE - KB3UON

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 typing up your telephone line, and a nice 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

spacer

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free