I don't think this statement is correct: "Since the NF of a AR SP432VDA is 0.55 dB and the gain is 15 dB if the coax..."
The 2meter VDA has a noise figure great than 1, stated to be about 1.1 dB NF; the difference is more than just gain. Thus the reason I suggest that he get the 2 meter VDG model with 0.55 dB NF :) http://www.advancedreceiver.com/page7.html Mark N8MH At 07:01 PM 3/10/2011 +0100, i8cvs 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
