Very good explanation Sent from my iPhone Andrew Rich
On 11/03/2011, at 4:01, "i8cvs" <[email protected]> wrote: > Hi Paul, K6HR > > The SSB and CW sensitivity of an IC 821H in 70 cm is less than 0.11uV > for a Signal to Noise ratio S/N= 10 dB > > Converting the above data into Noise Figure NF in dB we get: > -6 2 > ( Vin x 10 ) x 20 > NF = 10 log [ ------------------------ ] + 174 > dB 10 BW x S/N > > Where: > > Vin = input signal = 0.11 uV (microvolt) > BW = Band Width for SSB = 2400 Hz > S/N = Signal to Noise ratio = 10 dB i.e. 10 time in power ratio > > -6 2 > ( 0.11 x 10 ) x 20 > NF = 10 log [ --------------------------- ] + 174 = 4 dB > dB 10 2400 x 10 > > Showing a NF= 4 dB the IC 821 H seems to be a very good sensitive receiver > but if you want to improve the overall Noise Figure using an antenna mounted > preamplifier the Noise Figure of it must be less than 1 dB and infact the > Noise Figure of a AR SP432VDG is NF= 0.55 dB and the only change between > two models is only the gain because model VDG has a gain of 24 dB while the > model VDA has a gain of 15 dB > > The important thing here adding an antenna mounted preamplifier to a > receiver is not to overload the receiver with a very high noise coming from > the preamplifier gain. > > Addind RF stages in cascade the rule of thumb is the following one: > > "When adding a preamplifier if the noise increases by 10 dB than the overall > noise of the receiving system is not deteriorated " > > Since the NF of a AR SP432VDA is 0.55 dB and the gain is 15 dB if the coax > cable between the output of your preamplifier and receiver input is not too > long and lossy then you will not overload the IC 821 H because the S meter > reading with the preamplifier ON will be only about two S units of more > noise but the overall Noise Figure of your receiver system will be in the > range between 0.55 dB and 1 dB so that you will get a consistent improvement > in sensitivity. > > About the above matter also please read the following letters : > > http://www.db0anf.de/app/bbs/messages/show-AMSATBB4673 > > 73" de > > i8CVS Domenico > > ----- Original Message ----- > From: "Paul Delaney - K6HR" <[email protected]> > To: <[email protected]> > Sent: Wednesday, March 09, 2011 7:11 PM > Subject: [amsat-bb] IC-821H Frontend Overload? > > >> I'm setting up for satellite operation and considering the AR2 SP432VDG > 24db preamp. A friend suggests this will likely overload the frontend of the > radio (an 821H) The antennas are M2 eggbeaters. Would the SP432VDA 15db be a > better choice? >> >> Can anyone using these preamps give me some feedback on the 15db vs. 24db > preamps and which might be the best way to go considering the radio and > antennas I have? >> >> Paul Delaney >> [email protected] >> http://k6hr.dyndns.org:8080 >> _______________________________________________ >> 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 > > _______________________________________________ > 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 _______________________________________________ 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
