ampifier test setup procedure - RF Cafe Forums

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asaf
 Post subject: ampifier test setup procedure
Posted: Mon Oct 22, 2007 7:41 am 
 
Lieutenant
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Joined: Thu Oct 11, 2007 7:58 pm

Posts: 4

Hi,

When testing an amplifier I was told to connect dc, turn dc on and then connect testing cables. Is this the right procedure?

Thanks.
 
   
 
Feng
 Post subject:
Posted: Tue Oct 23, 2007 3:22 pm 
 
Captain
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Joined: Sun Mar 19, 2006 5:25 pm

Posts: 23

Location: Burnaby

I don't think this procedure fits for all the amplifiers such a high power one. You may check the specification of your instrument to ensure it.
 
   
 
nubbage
 Post subject:
Posted: Wed Oct 24, 2007 7:33 am 
 
General
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Joined: Fri Feb 17, 2006 12:07 pm

Posts: 268

Location: London UK

Feng is right: many medium to high power amps have a stability margin that is both source and load sensitive: that is they become unstable at certain load and source combinations of Reflection Coefficient magnitude and phase. I think a dude called Linvill first did the analysis of this for soldstate amps.

If the test cables are long and/or have extremely good dielectric insulation, it is possible that static charge can build up between the centre and outer. It therefore good practice to short the test cable between inner and outer before connecting the cables to the amp. Having connected them without risk of static damage, I would next turn the DC power on having ensured the source and load have a reasonably good match.
 
   
 
IR
 Post subject:
Posted: Sun Jan 27, 2008 3:36 am 
 
Site Admin
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Joined: Mon Jun 27, 2005 2:02 pm

Posts: 406

Location: Germany

Hello Asaf,

Since I also come from Israel and have worked in several RF companies,

I know the root of the fairy tale instruction you were told:

It is the fear that there might be an input power applied to the amplifier before power supply is applied, namely when the amplifier is connected as part of a cascade. When several amplifiers are connected in cascade that is the right thing to do but NOT when testing an amplifier as a stand alone unit.

What the other posts mentioned is 100% correct.

Posted  11/12/2012