[amsat-bb] Re: MMIC for LEO preamp?

i8cvs domenico.i8cvs at tin.it
Tue Dec 2 10:59:31 PST 2008

----- Original Message -----
From: "Curt Nixon" <cptcurt at flash.net>
To: "i8cvs" <domenico.i8cvs at tin.it>
Cc: "AMSAT-BB" <amsat-bb at amsat.org>
Sent: Tuesday, December 02, 2008 3:44 PM
Subject: Re: [amsat-bb] Re: MMIC for LEO preamp?

> Good Morning Domenico:
> In step 7 you wrote:
> 7)Without moving the audio and RF setting of the receiver start to play
>     tuning and adjusting everything is possible in your preamplifier i.e.
>     capacitors and inductances of the input network as well potentiometers
>     to set the active device current until switching the noise source ON
>    OFF the maximum variation on the AC voltmeter is reached  and this
>    condition correspond to the lovest possible Noise Figure obtainable
> Looking for MAXIMUM variation in noise...is this correct or should it be
looking for MINIMUM variation??
> Than ks..I'll give it a try.
> Curt
> KU8L
Hi Curt, KU8L

In  my previous message I wrote:

> Tuning the preamplifier for the lovest NF and switching the noise source
> from OFF to ON if you reach a difference from say 2 volt to 5 volt it is
> much better than if you get only a difference from say 2 to 4 volt because
> switching the noise source for the same ON/OFF noise levels you get a
> greater S/N ratio in the AC voltmeter  corresponding to a lover NF of
> your preamplifier.

I would like to add:

Supposing that in OFF condition you read 2 volt and 5 volt in ON condition
of the noise source it happen that during tuning procedure the gain of the
preamplifier changes so that the voltage in OFF condition changes as well
but you cannot move anything in the setup so that it is best to look for the
MAXIMUM variation of the ON/OFF voltages as a RATIO instead of the
difference because the ratio Von/Voff is indepentent from the gain and
greater the ratio lover the NF

73" de

i8CVS Domenico

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