[amsat-bb] Re: e: Satellite technical question
Thanks Domenico for the reply. You are correct the physical temperature and the equivalent noise temperature are not related. Bob wb4apr suggested that a 1/4 wave antenna in LEO has a noise equivalent temperature of ~ 150 k . What is the consensus of the group ? We are trying to do an uplink budget and one of the variables is the system temperature. nick -Original Message- From: i8cvs [mailto:domenico.i8...@tin.it] Sent: Monday, September 10, 2012 4:32 PM To: Nick Pugh; Amsat - BBs Subject: Re: [amsat-bb] Re: e: Satellite technical question Hi Nick , The equivalent noise temperature of an antenna do not depends by it's phisical temperature but only by the noise temperature emitted by the object that the main lobe of the antenna is looking. The equivalent noise temperature of the antenna radiation resistance do not depends by the phisical temperature of the antenna but only by the noise temperature emitted by the object that the main lobe of the antenna is looking. As an example, if you install a parabolic dish on the Nort Pool at very low temperature and a similar parabolic dish in the desert at the equator at high temperature and you point both the antennas toward the Sun than the received Sun Noise will be the same no matter the structural temperature of both dishes will be. Of coarse only the phisical temperature of the antenna preamplifiers and all the associated receivers phisical temperature must be the same. 73" de i8CVS Domenico - Original Message - From: "Nick Pugh" To: "'Nick Pugh'" ; Sent: Sunday, September 09, 2012 8:15 PM Subject: [amsat-bb] Re: e: Satellite technical question I am sorry I did not mean the physical temperature What I wanted is the equivalent noise temperature. Thanks for those who replied nick -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Nick Pugh Sent: Sunday, September 09, 2012 10:07 AM To: amsat-bb@amsat.org Subject: [amsat-bb] e: Satellite technical question e: Satellite technical question Assume a cubesat with a monopole ¼ wave antenna at 400 mhz. The satellite is in full sun with a 500km orbit. What is the antenna temperature in full sun and in eclipse? TNX in advance Nick CAPE Team ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: e: Satellite technical question
Hi Nick , The equivalent noise temperature of an antenna do not depends by it's phisical temperature but only by the noise temperature emitted by the object that the main lobe of the antenna is looking. The equivalent noise temperature of the antenna radiation resistance do not depends by the phisical temperature of the antenna but only by the noise temperature emitted by the object that the main lobe of the antenna is looking. As an example, if you install a parabolic dish on the Nort Pool at very low temperature and a similar parabolic dish in the desert at the equator at high temperature and you point both the antennas toward the Sun than the received Sun Noise will be the same no matter the structural temperature of both dishes will be. Of coarse only the phisical temperature of the antenna preamplifiers and all the associated receivers phisical temperature must be the same. 73" de i8CVS Domenico - Original Message - From: "Nick Pugh" To: "'Nick Pugh'" ; Sent: Sunday, September 09, 2012 8:15 PM Subject: [amsat-bb] Re: e: Satellite technical question I am sorry I did not mean the physical temperature What I wanted is the equivalent noise temperature. Thanks for those who replied nick -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Nick Pugh Sent: Sunday, September 09, 2012 10:07 AM To: amsat-bb@amsat.org Subject: [amsat-bb] e: Satellite technical question e: Satellite technical question Assume a cubesat with a monopole ¼ wave antenna at 400 mhz. The satellite is in full sun with a 500km orbit. What is the antenna temperature in full sun and in eclipse? TNX in advance Nick CAPE Team ___ Sent via AMSAT-BB@amsat.org. 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
[amsat-bb] Re: e: Satellite technical question
I am sorry I did not mean the physical temperature What I wanted is the equivalent noise temperature. Thanks for those who replied nick -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Nick Pugh Sent: Sunday, September 09, 2012 10:07 AM To: amsat-bb@amsat.org Subject: [amsat-bb] e: Satellite technical question e: Satellite technical question Assume a cubesat with a monopole ¼ wave antenna at 400 mhz. The satellite is in full sun with a 500km orbit. What is the antenna temperature in full sun and in eclipse? TNX in advance Nick CAPE Team ___ Sent via AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
[amsat-bb] Re: e: Satellite technical question
> Assume a cubesat with a monopole ¼ wave antenna at 400 mhz. >The satellite is in full sun with a 500km orbit. What is the antenna > temperature in full sun and in eclipse? It depends entirely on its color (surface properties). If it black it will get to about 55 farenheight in the sun and to about very cold in the dark. If it is white, it will get to about -60 F in the sun (Notice that is MINUS 60) and very cold in the dark. If it is clean shiny aluminum, it could get to +250 F in the sun and very cold in the dark all assuming they have no other way to conduct away heat. Those are steady state hot temps for the surfaces given. I dont remember the cold temps, though they will all reach the same very cold temps if they never see the sun. Notice that these are steady state. A metal sphere with these colors going in and out of eclipse will never reach these extremes because of their thermal mass that cannot get that hot in 60 minutes and cool down that much in 35 minutes of dark. Our basically black PCsat (solar panels mounted to the aluminum body with good conductivity only got to about room temperature in the sun and no colder than about freezing (32 F) in the dark every 90 minutes. But it was a shock to us when we designed a flip-out solar panel for a cubesat that is exposed on both sides to space. It gets to almost boiling on the sun side and down to about -70F in the dark... EVERY orbit. SO, I assumed that a thin tiny whip antenna could not conduct very much heat to the spacecraft, so its extremes will be high. But a piece of wire can easily handle these temps. But any solder joint that cannot communicate heat to/from the rest of the spacecraft might have problems. This is an off-the-cuff answer. Doing thermal in space is a real ART! Good luck. Bob, Wb4aPR > > > > TNX in advance > > > > Nick CAPE Team > > > > ___ > Sent via AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
