----- Original Message ----- From: "Glen Zook" gzook@yahoo.com To: "amsat-bb" amsat-bb@amsat.org; "Michael Chen" michael.bd5rv@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