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[Linrad] Re: Preamp WSE
- Subject: [Linrad] Re: Preamp WSE
- From: Jeremy Alexander <w7eme.org; jeremy@xxxxxxxxxxxxxxxx>
- Date: Fri, 20 Feb 2009 07:19:27 -0800 (PST)
--- On Thu, 2/19/09, Edward Cole <kl7uw@xxxxxxxxxxxxx> wrote:
> From: Edward Cole <kl7uw@xxxxxxxxxxxxx>
> Subject: [Linrad] Re: Preamp WSE
> To: linrad@xxxxxxxxxxxxxxxx
> Date: Thursday, February 19, 2009, 10:05 PM
> At 09:10 AM 2/19/2009, you wrote:
> >Aloha to all:
> >More elemental questions. What is a good amplifier
> level before
> >input to WSE RX144? If I have say LNAs at antennas and
> have maybe 15
> >dB gain at RX144, then inserting another 15 dB for each
> channel at
> >converter is working nicely.
> >What amount of signal amplification should supply to
> the RX144
> >channels? AND what effect is NF of second RF amplifiers
> in shack
> >have upon NF of system?
> >My interest is may I use a more economical RF amplifier
> at the back
> >of the converter and a good LNA at antenna to make
> required input to
> >WSE converter?
> >This has likely been convered before?
> >Jeremy w7eme
> I have a spreadsheet program that does the caculation for
> NF for two
> preamps and a receiver (or any three stages). The program
> uses this
> to determine MDS and full eme pathlink performance (SNR).
> the second preamp NF is reduced by the gain of the first
> preamp but
> any cable loss between the two preamps is added with the NF
> of preamp
> #2. NF = noise factor = 10^(noise fig/10). Much easier to
> do math
> with noise factors (ratio) than with noise figure (dB).
> So if your first preamp has a gain of say 16-dB, NF(2)/40
> is the
> contribution to total NF. A 1-dBNF second preamp will only
> contribute about 0.2 dB to the overall system noise figure.
> 73, Ed - KL7UW
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