Thank you for visiting RF Cafe! Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums RF Cafe Homepage Thank you for visiting RF Cafe!

How to Improve the IM3 - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement



Tiany
Post subject: how to improve the IM3 Posted: Wed Jun 10, 2009 2:57 am

Lieutenant

Joined: Sun Jun 07, 2009 9:14 am
Posts: 4
I am designing an amplifier
f:(30-400)MHz
Pout:>25W(CW) @IM3<-25dBc
The circuit and picture as following:
the Mosfets are two MRF9045.
the amplifier's IM3=-26dBc(at)270Mhz(at)25W(CW)
but the amplifier's IM3=-18dBc(at)400Mhz(at)25W(CW)
How can I improve the IM3?
thanks.





Top

VSWR
Post subject: Re: how to improve the IM3Posted: Sun Jun 14, 2009 11:40 pm

Captain

Joined: Sun Jan 11, 2004 4:44 pm
Posts: 8
Hey Tiany,

That's a nice project you have going there! I'm not the world's foremost expert on amplifier design, so I'm just shooting from the hip here. Of course one way to increase IP3 performance is to increase the current, but I assume you've already considered that. The next thing is to look for lossy components that are wasting the current you have available. I cringe just a bit at those coax transmission lines having such small radius bends when passing through the ferrites. Have you confirmed that they are not causing reflection problems? That could be a huge source of performance loss if they have really bad S11 or S21 because of that radius. Just a though - you've probably already thought of that too, but just figured I'd throw it out there.

Like I said, nice job!


Top

biff44
Post subject: Re: how to improve the IM3Posted: Mon Jun 15, 2009 9:40 am

Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 33
That is the subject of very many recent research papers!

Obviously, the bias point of the devices is critical. You can try varying the bias to get some improvement.

Output match is important, so try varying that. 2nd, and even 3rd harmonic match canbe important also, although your broadbandwidth will make that interesting.

Your choice of devices matters, try a different device. Some are more linear than others.

Then there are a raft of more complex methods, such as Doherty amplifiers, feedforward amplifiers, or predistorters. I would be tempted to try a predistorer (you can make one up using some diodes and a transformer).

Rich

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com

Top

susanspy
Post subject: Re: how to improve the IM3Posted: Wed Jul 29, 2009 11:22 am

Lieutenant

Joined: Wed Jul 29, 2009 11:11 am
Posts: 1
hello all,

i am susan here, i am interested in this post, but i too have the problem to improve the im3 so please any let me know about my problem.



thanks alot


cheers!!!!!!!!!!!!!!!


Top

RDO-RF
Post subject: Re: how to improve the IM3Posted: Thu Aug 06, 2009 2:09 pm

Captain


Joined: Wed Apr 08, 2009 7:53 am
Posts: 12
Hello,

I think the problem is hat you are having a small P1dB.. In the P1dB, the IM3 is -30dBc.. and you are having this just at 30W, where ideally you should have it at 90W. This cold be for many reasons, but perhaps the most important ones are: bias pioint and output matching.
First, i´ll try to find the best bias point for the implemented matching, if this doesn´t solve the problem, then i think you should review the output matching. Are you sure you are matching the output for the highest P1db?

Take care

_________________
web: http://www.rdo-labs.com







Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
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 Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

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

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !

height-line