Re: [amsat-bb] mmic preamp

[Glen Gardner <Glen.Gardner@xxxxxxxxxxx>]

Noise figure and noise floor are not the same thing.  Wether you can 
hear the atmospheric noise at UHF will depend mostly on the noise floor 
of the radio itself.
A good mmic preamp will add 2 dB to the noise floor of the radio.  A 
good gaasfet will add 1 dB or less.  There are a few mosfets which will 
add 1 to 2 dB noise.
A JFET preamp is unacceptablly high with around 4-6 dB , typical. 
 Ultimately, it is the reciever itself which determines the noise floor 
and wether you can hear natural radio noises. adding anything between 
the reciever and antenna adds noise, so lower noise figures are 
important.  In real terms, if the radio has a good noise figure to begin 
with , a 2 dB nf  mmic will perform quite well, but a gaasfet will be 
measurably quieter.

Glen


John B. Stephensen wrote:

>MMIC noise figures are 2 dB or above. This is much higher than the sky noise at
>435 MHz. A better choice would be a discrete FET. The ARRL Handbook for Radio
>Amateurs contains preamp designs for the VHF and UHF bands.
>
>73,
>
>John
>KD6OZH
>
>----- Original Message -----
>From: "K & R Yoksh" <yokshs@planetkc.com>
>To: "amsat-bb" <amsat-bb@AMSAT.Org>
>Sent: Saturday, 07 August, 2004 22:10 UTC
>Subject: [amsat-bb] mmic preamp
>
>
>  
>
>>Hello,
>>
>>Thanks for the couple of replies to my 70cm preamp question, although most
>>directed me to commercially made preamps. I am looking for plans for a
>>homebrew 70cm preamp.
>>
>>Before I re-invent the wheel, who's got a simple, proven MMIC preamp design
>>for 70cm? Reply here or to k0kn at amsat dot org.
>>
>>Thanks,
>>
>>Kyle Yoksh
>>K0KN
>>Olathe, Kansas
>>Amsat# 35249
>>----
>>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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>>    
>>
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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>  
>

-- 
Glen E. Gardner, Jr.
AA8C
AMSAT MEMBER 10593



http://members.bellatlantic.net/~vze24qhw/index.html
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