[Moon] LNA gain

jewell at btinternet.com jewell at btinternet.com
Thu Jul 26 22:30:55 CEST 2018


Jan,Higher gain preamps are usually used on EME in order to overcome second stage losses from, for example, coaxial cable from the dish to the shack, poor transverter noise figure, insertion loss of a bias tee (if used) and maybe an additional band pass filter if you have a lot of strong out of band signals.The usual rule of thumb is that the noise floor of the receive system should incease by 10-15dB when the LNA is switched on. The input must be terminated in 50R for this test. It is unwise to rely on the antenna match at this stage.Yes, the additional gain of the LNA will decrease the receive system dynamic range by the amount of the effective additional gain, but for most microwave EME signals that will not be a problem as signals are usually not that strong.If you are on 144MHz EME the gain rule may not apply as interference can become a more significant problem, but on the low noise microwave bands it is an essential stage in commissioning a new system.
73 de Sam, G4DDK




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On Thursday, July 26, 2018, 9:21 pm, Jan Vadilijev via Moon <moon at moonbounce.info> wrote:

Hi,

I got good answers for relay, but I need to know something else to play
with/improve RX.
How influence the gain of LNA to transverter. I know if is to low but I'm
not sure if the signal of LNA is to "big" for transverter?
For example I have from RX side feed relay then LNA and little piece of
coax cable directly to transverter. Attenuation between LNA and transverter
is only 3-5dB but the gain of LNA is over 25dB...20dB reserve..I now some
have transverter 10meter away and need gain..
what will do this 20dB  increase the minimum RX level for 20dB up? Sorry I
don't understand that...


I'm using Kuhne design transverter.
The question is if I need to worry about LNA gain( how is the right way to
set gain...need any attenuator to put between)  or to put it together and
that is ?


thanks for your answer
73 Jan
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