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


jdow
 

If you see no signs of overload with no LNA then leave it out. It saves power. You're greener or something like that. If you have nearby large signals from time to time the SAW filter in that LNA may help. You know your local conditions, I don't. So all I can do is conjecture and that's not what you want.

One caveat here - the S+N/N ratio you should test at is something on the order of 6 db to 9 dB to have the greatest sensitivity to overall sensitivity differences. Testing at 20 dB or 30 dB is not so good. Of course, testing at 50 dB is usually worthless.

{^_^}

On 2017-11-18 10:49, Ruben Navarro Huedo (EA5BZ) wrote:
Hello again:
This evening i was playing and doing some tests.
I have around the same SNR with and without my LNA+HPF+SAW BPF ( https://store.uputronics.com/index.php?route=product/product&path=59&product_id=94 )
This is how i did the test:
I used my VNA connected to a little whip-antenna to generate an ON-AIR reference signal of 137.5 Mhz.
With my Airspy connected to my turnstile i played with gain to have the best SNR.
Then i did the same without the VNA and SNR were around the same.
Whit this test result i think the best is NOT use LNA.
What do you think?
Thank's again :-)

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