Some calculations about GAIN, LNA, ATTENUATORS, COAX...


Ruben Navarro Huedo (EA5BZ)
 
Edited

Hello friends:
My knowledge of RF concepts are medium to low.
I am learning a lot reading this group.
Here are some thinkings about my setup at this moment:

Using an Airspy R2.
Main use are frequencies from 130 to 150 Mhz (Mainly 137 SAT Frequencies).
I am using:
Antenna --> Around 6 meters CO22 Coax Cable--> LNA with HPF and BPF included for 137.5Mhz ( https://store.uputronics.com/index.php?route=product/product&path=59&product_id=94 ) --> 30 meters Ecoflex 10 Coax cable --> Airspy R2

Ecoflex 10 has an attenuation of around 5db in 100m (144mhz). Then i will have 1.5db of attenuation in 30 meters.
Lets estimate a loss in connectors and converters of around 1 db more ¿? ----> Then i have around 2.5db of total attenuation.

With this calculation i think my LNA has too much gain. (M
anufacturer talks about 23db gain).
Is this correct?
I will have best results with a 15db attenuator after the LNA.

I am having the best results using GAIN 10 and Linearity.
What do you think about all this?

Thank's a lot.


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