Yes, thank you for that detailed explanation and analysis. Best 73, Elan
--- On Sun, 12/20/09, i8cvs <[email protected]> wrote: > From: i8cvs <[email protected]> > Subject: Re: [amsat-bb] Re: Preamp location tech question > To: "Elan Portnoy" <[email protected]>, "amsat bb" <[email protected]> > Date: Sunday, December 20, 2009, 4:23 PM > Hi Elan, > > You don't mention the model of preamplifiers from ARR that > you are > using but I suppose that you got the better between the > tree models > available i.e. the SP144VDG 144-148 MHz with NF = 0.55 dB > and the > SP432VDG 420-450 MHz with NF= 0.55 dB > > Now if you add between the antenna and preamplifiers 50 > feet of coax cable > LMR400 then the loss of 0.75 dB at 144 MHz and the loss of > 1.35 dB at > 435 MHz adds to the Noise Figure of your preamplifiers so > that it is like > to have: > > a 144 MHz preamplifier with an overall NF = 0.55 + 0.75 = > 1.3 dB > a 435 MHz preamplifier with an overall NF = 0.55 + 1.35 = > 1.9 dB > > Supposing that you have the preamplifier antenna mounted > working out > the numbars for 144 MHz we get: > > Noise Figure NF = 0.55 dB > Noise Factor F = 10^(NF/10) = 10^0.055 = 1.13 > The equivalent Noise Temperature T = (1.13 -1 ) x 290 > = 39 kelvin > If you live in a rural area at 144 MHz the equivalent Noise > Antenna > Temperature T1=200 kelvin so that your Tsys1=39+200= 239 > kelvin > > Let see what happens if you mount the preamplifier in the > shack: > > Overall Noise Figure = 0.55 + 0.75 = 1.3 dB > Overall Noise Factor F = 10^(10/1.3) = 10^0.13 = > 1.35 > The equivalent Noise Temperature T = (1.35-1) x 290 = 101 > kelvin > Since the antenna is the same Tsys2 = 101+200 = 301 kelvin > > The improvement putting the preamplifier antenna mounted > against shack mounted is > > 10 log (Tsys2 / Tsys1 ) = 10 > log (301 / 239 ) = 1.0 dB > 10 > > > 10 > > The improvement at 144 MHz is very small because the > Antenna > Temperature = 200 kelvin predominates. > > Let see the situation for 435 MHz were the Antenna > Temperature is > less and only 50 kelvin in a rural area > > Preamplifier antenna mounted: > > Noise Figure NF = 0.55 dB > Noise Factor F = 10^(NF/10) = 10^0.055 = 1.13 > The equivalent Noise Temperature T = (1.13 -1 ) x 290 > = 39 kelvin > If you live in a rural area the equivalent Noise Antenna > Temperature > T1 = 50 kelvin so that your Tsys1 = 39 + 50 = 89 kelvin > > > Preamplifier in the shak: > > Overall Noise Figure = 0.55 + 1.35 = 1.9 dB > Overall Noise Factor F = 10^(10/1.9) = 10^0.19 = > 1.55 > The equivalent Noise Temperature T = (1.55-1) x 290 = 159 > kelvin > Since the antenna is the same Tsys2 = 159 +50 = 209 kelvin > > > The improvement with the preamplifier antenna mounted > against > shack mounted is > > 10 log (Tsys2 / Tsys1 ) = 10 > log (209 / 89 ) = 3.7 dB > 10 > > > 10 > > The improvement in 435 MHz is greater because the Antenna > Temperature = 50 kelvin do not predominates over the > equivalent > Preamplifier Noise Temperature. > > By the way 3.7 dB of more swing in the S meter over the > noise is > more than half of a S point so that in your situation I > would put > only the 435 MHz preamplifier at the antenna and would > leave > the 144 MHz preamplifier in the shack. > > CONCLUSION: > > Since the loss of 50 feet of LMR400 is very small the > advantage > in (S+N)/N ratio to put the low noise preamplifiers antenna > mounted > is only 1 db at 144 MHz and 3.7 dB at 435 MHz in a rural > area. > If the installation is made in a suburban area or in a > urban area where > the equivalent Antenna Noise level is greater and > predominates then > the advantages are accordingly less. > > I hope this helps. > > 73" de > > i8CVS Domenico > > ----- Original Message ----- > From: "Elan Portnoy" <[email protected]> > To: "amsat bb" <[email protected]> > Sent: Sunday, December 20, 2009 6:40 PM > Subject: [amsat-bb] Re: Preamp location tech question > > > > Well, it's clear what I should do. Will try remounting > on masts as soon as > weather permits. Looking forward to improvements in > performance. > > > > Thanks to all and happy holidays! > > > > _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
