Using isolator between driver stage and final stage of RF power amplifier

[Mabrok]

Dear all,

I have two amplifiers "driver stage and final stage", and will perform power measurements. Usually, we use isolator between two stages for safety purposes. But, unfortunately I do not have isolator at my lab and do not have budget to buy new one. As per checked, the high power one is quite expensive. So, If i tested two amplifiers separately and found them well matched to 50 ohm. So, could perform measurements by connected them directly without using isolator? FYi, power out of driver stage about 10 watt, and from final stage about 25 watt for 3.4-3.6 GHz frequency band. Please advise. Thank you

 

[dick_freebird]

Every blocking cap is an isolator, questions are to what voltage and how reliably. A bias-T of acceptable rating (=?) might be the handiest, connectorized option but the shield is not isolated, only the center.

A RF xfmr and two SMAs?

 

[biff44]

well....an amplifier that is perfectly stable WITH an interstage isolator, might remain stable when it is removed, or might break into oscillations.

i would slowly increase the bias voltage with the amps in cascade, and watch the output with a spectrum analyzer, and shut it down if it goes rogue on you.

I feel 90% sure you will not have an issue.

 

[biff44]

if you want to buy a USED isolator, they are pretty affordable!

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not sure of the power rating of the 2nd one

 

[BigBoss]

Isolators are used to protect a PA in case of highly mismatch or failure. Otherwise it won't be necessary..

 

[AMS012]

Matching is not the only critical thing in this case. The second stage should be able to handle the RMS and peak power/voltage swing put out by the preceding stage. I reckon you would have checked both.