Receiver Noise Figure

[kommanche]

Hi,

As far as I know receiver NF's are close to the LNA NF according to the famous equation. So it should be in the order of 2-3. When I look at some systems like Miteq D282 Downconverter, I saw 16 dB NF. How can it be possible?

Thanks,

 

[flatulent]

Mixers are notorious for having poor noise figures. That is why receivers have RF amplifiers in front of the mixer.

 

[kommanche]

Mixers are notorious for having poor noise figures. That is why receivers have RF amplifiers in front of the mixer.

OK. Can you comment on high noise figure specs for Miteq downconverter? Isn't 16 dB much high?

 

[0dBc]

Not all downconverters have an LNA at the front, especially the ones that have a wide input range. Most probably Miteq's downconverter has an input step attenuator followed by a filter followed by mixer/LNA or LNA/mixer. So 16 dB isn't really that high considering the insertion loss caused by all these.

Hi,

As far as I know receiver NF's are close to the LNA NF according to the famous equation. So it should be in the order of 2-3. When I look at some systems like Miteq D282 Downconverter, I saw 16 dB NF. How can it be possible?

Thanks,

 

[pstuckey]

In receiver design there is always a trade-off between maximizing sensitivity (low noise figure) and maximizing linearity (high Intercept Point).

It appears likely that Miteq chose to maximize linearity. You can always lower the noise figure by putting your own LNA in front of the Miteq part. Be aware that by doing this you'll be trading some linearity for better noise figure though.