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LNA Out of band Frequency Rejection Question

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out of band rejection vs out of band gain

I need some clarification on this quoted specification

"For the purposes of rejecting undesired signals, the active portion of the GPS antenna shall have the following out-of-band rejection filter characteristic requirements as measured at the antenna assembly...

>25 dB at +/- 50 MHz of 1575.42 MHz"

My question is this, let's assume the LNA has a gain of 25 dB and I was measuring the performance of the LNA. Assuming calibrated VNA would I expect signals outside of +/- 50 MHz to be 0dB (25 dB down from the gain) or -25 dB (50 dB down from the gain) in order to meet spec?

I interpreted my requirements such that a -25 dB filter would be sufficient, is this the correct way to think?

thanks in advance
 

Hi,
I agree with your interpretation, the response should be 25dB or more down on the main lobe +/-50MHz away from the centre frequency.
Bob.
 

Consider SAW or dielectric filter to meet your requirement.
 

I think that out of band signal will be 25db down from the output signal of LNA..
 

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