[amsat-bb] Re: 70cm preamp

i8cvs domenico.i8cvs at tin.it
Fri Nov 27 03:13:41 PST 2009


----- Original Message -----
From: "Glen Zook" <gzook at yahoo.com>
To: "amsat-bb" <amsat-bb at amsat.org>; "Michael Chen"
<michael.bd5rv at gmail.com>
Sent: Friday, November 27, 2009 1:22 AM
Subject: [amsat-bb] Re: 70cm preamp

> Ramsey actually has a pretty good low noise preamp for 70 cm and those are
cheap.  Takes about 15 minutes to assemble the kit.  I do recommend
replacing the fixed capacitor across the coil with a variable.  That way you
don't have to "fiddle" with bending the coil to tune it.  You just "set" the
coil and then use the variable to adjust the actual frequency.
>
> I bought one of the 70 cm kits and one of the 222 MHz kits several months
ago.  Both of them work very well.  The 222 MHz has a slug tuned coil but
the 70 cm is fixed and you are supposedly to tune it by moving the turns
around.  But, MUCH easier to adjust if you replace the fixed capacitor with
a variable.
>
> I am almost sure that they ship internationally.  The kits are less than
$15 U.S.
>
> Glen, K9STH
>
> Website:  http://k9sth.com
>
Hi Glen, K9STH

But how do you adjust the input of your low noise preamplifier for the
lovest Noise Figure ?

To do that you cannot  just "set" the coil and then use the variable to
adjust the actual frequency for maximum output but you need a Noise
Source and adjust the coil and the variable for the maximum S/N ratio
and this can be done manually or automatically using a Noise Figure
Meter.

This is why to build a low noise preamplifier without to have a Noise
Figure Meter or a SINAD meter is like to walk blindly.

73" de

i8CVS Domenico










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