[linrad] Re: Fwd: [softrock40] v7.0 kit run or not?

[Robert McGwier <comcast.net; rwmcgwier@xxxxxxxxxxxxxxxx>]

The Softrock 7 should be considered strictly a mixer and coupled with 
the software,  an IF receiver.

The SR7 has an MDS of -109 dBm (typical,  I measured one at -107 dBm and 
another at -110 dBm).  So the system NF will be high without gain in 
front of it.  The VHF preamp in your system should determine  the system 
noise temperature/NF as in all such systems and all things in front of 
SR7 will need to provide both the noise figure plus gain to overcome 
losses and noise floor of the SR7.  If you are attempting to do EME and 
want a decent noise temperature (sky + antenna) to be around 60-ish 
degrees Kelvin and a noise floor around -180 dBm/Hz,  you need a lot of 
gain to shove the weakest signal in 500 Hz at (say) -153 dBm above the 
noise floor of the SR7.

There are loads of web resources and practical examples but some 
relevant ones would include

Chomski's :  http://www.nd2x.net/wa6py-MDS.html

http://www.satsig.net/noise.htm

http://www.mth.msu.edu/~maccluer/Lna/noisetemp.html


and one really needs to use a good tool to help with all of this and I 
recommend a free one:

http://www.hp.woodshot.com/


Bob
N4HY




w3sz wrote:
> Hi, Josh,
>
> I am not an RF expert, so take ANYTHING I say with a large grain of 
> salt.  I was waiting for the real experts to chime in, but haven't 
> seen any answers from them, so here goes ;)
>
>
> 73,
>
> Roger
> W3SZ


--
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity.  Guilty as charged!


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