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


You are correct.  23 to 25 dB of gain is far too much for the AirSpy products.  Instead of using that preamp with filters, I'd suggest using a single J-310 'narrow band' preamp.  It will give  you about 12 to 13 dB of gain at the WXsat frequencies.  Thats plenty to overcome the cable loss and drop the NF of the AirSpy in your installation to around 2 to 2.5 dB.  The AirSpy products I've had and one I still have exhibit a NF around 4 to 5 dB.  That's plenty good for HF and likely even the WX sats.  However, a single J-310 preamp narrow banded design will do you far more good than a broadband 23 dB gain preamp.  I'd reference a www search on N6CA's U-310 preamp.  He presents necessary data for 6, 2, and 1.25 meters.  I believe the design is also covered in a number of the ARRL publications addressing amateur satellite communications.

Dave - WØLEV

On Fri, Nov 17, 2017 at 1:16 PM, Ruben Navarro Huedo (EA5BZ) <runahue@...> wrote:
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 ( ) --> 30 meters Ecoflex 10 Coax cable --> Airspy R2

Ecoflex 10 has an attenuation of around 5db in 100m. 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.

Dave - WØLEV
Just Let Darwin Work

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