[amsat-bb] Re: Preamps??

[James Duffey]

Jerry - Preamps at the antenna help. They help a lot if you have a  
setup that is limited by receiver performance and/or feedline loss.  
They won't help if you are limited by the noise environment. They  
usually help a lot for satellite operation as there is usually not  
much external noise when the antenna is pointed to empty space rather  
than to your neighbor's lamp dimmer.

For two meters a grounded gate preamplifier based on the U310 is a  
good choice:

< http://www.ham-radio.com/n6ca/50MHz/50appnotes/U310.html >

Unfortunately, the TO-52 style U310 has gotten pretty expensive; I  
think they are $11 a piece from Mouser! Still this is a tried and true  
design that is stable and easy to build. You might try the more widely  
available and cheaper J310, which is the same part in a plastic package.

MOSFETs also make a good preamp. Here are a couple using the BF981:

< http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=9247 >

< http://www.geocities.com/icdx_australia/bf981preamp.html >

There are lots of other designs out there. The old ARRL handbooks from  
the 90s had some nice designs for both dual gate MOSFETs and GaAs  
FETs. If you use the same feed line and antenna for transmit, you will  
need to add relays to switch around the preamp when you transmit.

Advanced Receiver Research, ARR, is a source of commercial  
preamplifiers, and there are some models that have built in RF  
switching.

There are other vendors, with higher prices.

A preamp is a good investment to upgrade your station, but it is not a  
cure all, particularly if you are dominated by terrestrial noise  
source. - DUffey



On Apr 12, 2009, at 6:22 AM, Jerry Felts wrote:

> I've seen Preamps mentioned several times now so Who? What? Where? I  
> have
> not seen them in the AES catalog I got the other day.  Can you build  
> one?
> Need info on them!!
>
> Jerry - NR5A
>
> -- 
> Jerry - NR5A - South Dakota
> www.freewebs.com/nr5a
> http://groups.yahoo.com/group/Minimalist_QRP_Transceivers/
> http://www.cakewalkblogs.com/nr5asminimalradio/index.aspx
> http://nr5abeaconblog.blogspot.com/
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--
KK6MC
James Duffey
Cedar Crest NM