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 RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Anritsu Alliance Test Equipment Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Bittele Centric RF Conduct RF Copper Mountain Technologies Empower RF everything RF Exodus Advanced Communications Innovative Power Products ISOTEC KR Filters Lotus Systems PCB Directory Rigol RF Superstore San Francisco Circuits Reactel RFCT TotalTemp Technologies Triad RF Systems Windfreak Technologies Withwave LadyBug Technologies Wireless Telecom Group Sponsorship Rates RF Cafe Software Resources Vintage Magazines Thank you for visiting RF Cafe!
DC-70 GHz RF Cables - RF Cafe

clarification on the reference article - LNA's using 3db QH - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

NOTICE: The original RF Cafe Forum is available again for reading, and the new RF Cafe Blog is an active board.

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster

balajisu

Post subject: clarification on the reference article - LNA's using 3db QH Posted: Thu Jul 06, 2006 9:51 am

Captain

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 24

Location: Germantown,MD

Hi

Below is the link from the reference section. This paper uses Quadrature Hybrid cascaded with LNA to get better VSWR. I believe the Quadrature Hybrid provides 3dB loss. Assuming the LNA is designed to have a very low NF . Is it true that the net NF of the cascaded system will be closer to the NF/loss provided by the Quadrature Hybrid. So if this is true what is the true significance of this design technique. Any comments in this regard would be appreciated.

www.rfcafe.com/references/articles/ LNA_Design_Using_Quadrature_Hybrid.PDF

Thanks

Balaji

Top

Joe

Post subject: LNAPosted: Thu Jul 06, 2006 3:27 pm

Captain

Joined: Fri Feb 17, 2006 6:25 pm

Posts: 6

Location: US

The increase in noise figure will be due to the actual resistive loss of the coupler. This could be .1dB, .25dB .5dB, or even 1dB. The actual loss is dependent on the frequency and the type of construction. The 3dB referred to is the result of the split with 1/2 the power going to each output. It is not real loss.

The signal and noise at the input are both split, amplified by the amplifier in each arm, and recombined. The net gain of the system is the gain of one amplifier (they are both the same to maintain balance) less the real loss of the coupler. The noise figure is the noise figure of the amplifier stage degraded by the resistive losses of the input hybrid. This will be tenths of dB's not 3dB.

The advantage of the balanced amplifier is that it is easier to match, partictularly if a wider bandwidth is required. The noise figure will be a few tenths of a dB worse than not using the hybrid. In most cases this is a good tradeoff.

Top

balajisu

Post subject: Posted: Thu Jul 06, 2006 5:17 pm

Captain

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 24

Location: Germantown,MD

thanks for clarifying.

regards

Balaji

Posted  11/12/2012

RIGOL Technologies (test equipment) - RF Cafe
Exodus Advanced Communications Best in Class RF Amplifier SSPAs
RF Cascade Workbook 2018 by RF Cafe

Exodus Advanced Communications Best in Class RF Amplifier SSPAs

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

These Are Available for Free

 

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 tying 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