need to measure the input impedance of a LNA

[Samy_75]

LNA measurement

Hi Experts,

I need to measure the input impedance of a LNA designed to amplify RF signals around 80dBm. However, the source of my VNA can only be decreased down to -20dBm. .....Any idea of how I can do this measurement?

Thanks,

Samy

 

[kspalla]

LNA measurement

Check is it 80dBm or -80dBm.
Put pad of 60dB or so to get -80dBm.
VNA normally can be decrease to -80 dBm. Check the data sheets.

With pad you will get the wrong measurements if you do not carry the calibration with the pad.

 

[Samy_75]

Re: LNA measurement

Hello Kspala,

As you noticed, it is -80dBm and not 80dBm (typo error)...sorry for the inconvenience. Moreover, I confirm you that on the VNA, I use, the level of the power source can only be decreased down to -20dBm.

Your help is appreciated. Thanks

Samy

 

[kspalla]

LNA measurement

Then go to the method I said above put pad to get -80dBm, then calibrate the VNA.

 

[Samy_75]

Re: LNA measurement

Hi kspala,

When you say pad, you mean attenuator.....is it right?
Thanks for ur help.

Samy

 

[VSWR]

Re: LNA measurement

pad = attenuator

 

[kspalla]

LNA measurement

Yes you are right .
Pad in short means attenuation pad.
May I know why you need to test the LNA at -80dBm.
You can as well test at -30dBm or so.I mean if it works fine at higher powers(-30dBm even it can go slightly more than input P1dB) it means that he LNA will work at lower power too.
What are your LNA specifications?
Please share with us.

 

[RFDave]

Re: LNA measurement

As long as your LNA is operating well below the 1 dB compression point (20 dB or so) then the input impedance isn't a function of the power. If the P1 dB of you LNA is -5 dBm or higher, just measure it at -20 dBm. If you use 60 dB of attenuation, all you are going to do is to be measuring the attenuator.

Dave
www.keystoneradio.com

 

[Element_115]

Re: LNA measurement

Just to give yourself confidence of your input impedance measurement, just
measure the LNA with Pin= +5dBm, then 0 dBm , -5, -10,-15,-20 dBm. So
you will be able to see the effects as a function of Pin. As it was
mentioned before, the impedance will only start to change as you operate
around the P1dB point.

Cheers