April 2010 - AMSAT-BB - mailman.amsat.org

X-37B NORAD 36514
by JC-Aveni 23 Apr '10

23 Apr '10

US Space track X-37B OTV1 Id NORAD : 36514 ; UN Id : 2010 015A 73 Jean-Claude TK5GH

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QubeSat structure question
by William Leijenaar 23 Apr '10

23 Apr '10

Dear AMSATs, I have a question concerning CubeSats structures. I am looking for a way to have a total space of a 1U (10cm x 10cm x 10cm) CubeSat, of which 0.5U (10cm x 10cm x 5cm) is used for electronics and battery and the other 0.5U will be used for light weight deployable solar panels. Has this been done before ? Any ideas ? 73 de William Leijenaar PE1RAH

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Re: Arecibo on 432 MHz Moon Bounce (some calculations)
by Idle-Tyme 23 Apr '10

23 Apr '10

Wow that's all messed up? I'm 52 and this is the very first time i have ever seen anything like this and i have been dealing with science worldwide all my life. wow. Joe The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com On 4/22/2010 1:14 PM, Sil - ZL2CIA wrote: > Idle-Tyme wrote: >> On 4/21/2010 8:25 PM, i8cvs wrote: >>>> Comma or no comma, shouldn't matter >>>> 1000 mega watts or 1,000 Mega watts is still one thousand million >>>> watts! NOT one thousands watts. true? >>>> >>>> The Original Rolling Ball Clock >>>> Idle Tyme >>>> Idle-Tyme.com >>>> http://www.idle-tyme.com >>>> >>> Hi Idle-Tyme >>> >>> I don't agree with your statement: >>> >>> 1000 mega watt are one thousand million watt >>> 1,000 mega watt or 1.000 mega watt is only one million watt because >>> zero after the comma means nothing like 1,0000000000000 is still >>> one million watt or 1 MW >> NO! it's a comma, not a decimal point! it's one thousand, one >> thousand written 1000 or 1,000 is still one thousand they are exactly >> the same. > That's only true in the English speaking world, and this is the cause > of the confusion in this debate. > > In the Netherlands (and most of Europe), you would write one thousand > million watts as 1.000 megawatts. > > The decimal indicator in Europe is a comma. > For example, > 1,5 means one and a half > 1.000.000 means one million. > > Sil > (ex PA3HIL) > >

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Re: Arecibo on 432 MHz Moon Bounce (some calculations)
by Stephen Melachrinos 23 Apr '10

23 Apr '10

Ah, but this focuses on my question: Why is ERP referenced to a dipole? Why did someone assume that Arecibo's stated gain of 60 dB was dBd and not dBi? I've never seen the gain of a dish antenna used in satellite work quoted in dBd. All of the references for calculating gain are based on the isotropic reference. And all of the usages I have seen (in professional satellite work) use ERP and EiRP interchangeably, and the i in EiRP is used to explicitly state "referenced to isotropic." In fact, the amateur community is the only place where there is a fascination with the dipole reference. The dBd specs are useless for any real calculation purposes. Satcom engineering is much simpler if everyone quotes isotropic, and all commercial/government/military satellite link budgets are based on isotropic references. Steve Melachrinos W3HF (Professional) Satcom Engineer since 1979 > "ERP is about 243 MW" and > that comes from the conversion from dBi to dBd.

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Double da Donation!
by Clint BRADFORD 23 Apr '10

23 Apr '10

A reminder - You can make contributions online in the AMSAT Store - and the Dayton Amateur Radio Association (DARA) will match one-for-one any donations made to AMSAT between now and June 30, 2010 up to a maximum of $5,000. No, only your half is tax-deductible for you ... (grin) What a great way to show your support of amateur satellites! Please tell your ham friends and club members! Clint Bradford, K6LCS 909-241-7666

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Re: Arecibo on 432 MHz Moon Bounce (some calculations)
by Edward Cole 23 Apr '10

23 Apr '10

At 02:20 AM 4/22/2010, Stephen Melachrinos wrote: >Ah, but this focuses on my question: Why is ERP referenced to a >dipole? Why did someone assume that Arecibo's stated gain of 60 dB >was dBd and not dBi? I've never seen the gain of a dish antenna used >in satellite work quoted in dBd. All of the references for >calculating gain are based on the isotropic reference. And all of >the usages I have seen (in professional satellite work) use ERP and >EiRP interchangeably, and the i in EiRP is used to explicitly state >"referenced to isotropic." > >In fact, the amateur community is the only place where there is a >fascination with the dipole reference. > >The dBd specs are useless for any real calculation purposes. Satcom >engineering is much simpler if everyone quotes isotropic, and all >commercial/government/military satellite link budgets are based on >isotropic references. > >Steve Melachrinos >W3HF >(Professional) Satcom Engineer since 1979 > > > > "ERP is about 243 MW" and > > that comes from the conversion from dBi to dBd. >_______________________________________________ >Sent via AMSAT-BB(a)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 In fact the first gain number published over a month ago was 58 dBi. Then I suppose a bunch of hams complained that they didn't understand isotropic gain so the Arecibo folks kindly converted the number to 60 dBd. (i.e. unity isotropic gain, dBi=0, is what a true omni-directional antenna produces in free space) Does anyone on this reflector know the formula for calculating gain of a parabolic dish (Yes, I know-I'm asking if you know)? Did you know that Arecibo dish is spherical and not parabolic? So we can only use the gain number they provide (BTW the UHF line-feed corrects for spherical aberration of the dish surface at Arecibo). Arecibo can track a small amount of angle "because" the dish is spherical. It is my understanding (might be wrong on this) the line-feed can adjust for the amount of surface irradiated (which will change the gain). The formula normally used in radio astronomy and mw engineering is in terms of dBi. Most (not all) eme hams use dBi vs dBd. I am really amazed at this thread on amsat-bb. I thought the satellite community was more globally oriented (International). The different convention in expressing decimal numbers (aka using comma or period) is pretty well known (I thought). US/UK use period and most EU use comma. Most antenna analysis sw express gain in dBi 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010 DUBUS Magazine USA Rep dubususa(a)hotmail.com ======================================

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Re: Arecibo on 432 MHz Moon Bounce (some calculations)
by Stephen Melachrinos 23 Apr '10

23 Apr '10

Nigel - There are lots of lots of reasons ... 1. All link budgets use a path loss calculation that's also referenced to an isotropic radiator. If you use antenna gain referenced to a dipole, you'll have to add back the gain of the dipole (referenced to the isotropic radiator). 2. It's the standard way of calculating gain for virtually all professionals in the satellite, radar, deep space, avionics, microwave and many other fields. 3. Arguably, dBi is less ambiguous that dBd. By definition, an isotropic reference has the same gain (0 dB) in all directions. A dipole has a directional pattern, so dBd only makes sense if you also define the direction. I believe the assumption is gain broadside to the antenna, but that is still an assumption. 4. If you don't want to actually do link budgets, so you say reason #1 above is irrelevant, then your only real purpose is to compare two different antennas. And then the difference is always going to be dB, whether the two antennas are specified in dBi or dBd. So I still say to use the universal, unambiguous standard. 5. Finally, and most significantly, your statement "Why would I believe, or want to use, something I can neither have, use or measure? An isotropic antenna doesn't exist." is just as applicable to the ideal dipole that is your reference for dBd as it is to an isotropic radiator. You can't build a dipole that has zero resistance along its physical length, you can't build a dipole that has zero interaction with its feedline, and you certainly can't achieve any placement that perfectly represents the "dipole in free space" assumption upon which the dBd reference is based. In summary, there are plenty of reasons whay virtually anyone who builds or uses antennas for a living, does it in dBi Steve W3HF > Apr 22, 2010 09:15:04 AM, nigel(a)ngunn.net wrote: > I guess because it's impossible to build an isotropic radiator and therefore just as impossible to measure it. > Why would I believe, or want to use, something I can neither have, use or measure? > > An isotropic antenna doesn't exist. > > > In fact, the amateur community is the only place where there is a fascination with the dipole reference.

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Tickets from Space
by Clint Bradford 23 Apr '10

23 Apr '10

PIPS Technology has developed a license plate recognition system that uses two cameras on the ground and one mounted on a satellite to catch speeders. Blog entry at ... http://tinyurl.com/39c9hlp Clint, K6LCS

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Michigan Grid Activation; EN74
by Doug Papay 23 Apr '10

23 Apr '10

All, I will be active this Thursday-Saturday from the northern lower peninsula of Michigan--primarily grid square EN74. Despite the fact that Traverse City is located within EN74, this is a rarely activated grid on satellite. I plan to operate as many passes as my schedule & time permits to give the opportunity for those who don't have this grid to put it in their logbook. Since I will only have the capability to operate FM voice satellite, my operations will be limited to AO-27 and SO-50, as AO-51 is in mode V/S until Sunday evening & HO-68 is not scheduled for FM operation this weekend. My tentative schedule is as follows: Thursday 22-Apr-2010 AO-27 18:48z - 19:03z (from wherever I am at the time, most likely EN63; possibly EN64) Friday 23-Apr-2010 SO-50 04:04z - 04:18z (upon request) SO-50 12:35z - 12:48z AO-27 18:21z - 18:34z* AO-27 20:00z - 20:13z* Saturday 24-Apr-2010 SO-50 04:34z - 04:47z (upon request) SO-50 11:24z - 11:37z AO-27 17:53z - 18:05z* AO-27 19:31z - 19:45z (maybe; EN63) *If there is significant interest, I will consider activating EN64 on Friday and/or Saturday afternoon. Send me an email off-list if you need EN64, if I have significant interest I will make an effort to activate this grid as well during my trip. I will QSL upon request, just send me an email and I will send you a card. No SASE needed, but always appreciated. 73, Doug KD8CAO

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Re: Arecibo on 432 MHz Moon Bounce (some calculations)
by i8cvs 23 Apr '10

23 Apr '10

----- Original Message ----- From: "Sil - ZL2CIA" <zl2cia(a)amsat.org> To: "Idle-Tyme" <nss(a)mwt.net> Cc: "i8cvs" <domenico.i8cvs(a)tin.it>; "AMSAT-BB" <amsat-bb(a)amsat.org> Sent: Thursday, April 22, 2010 8:14 PM Subject: Re: [amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations) > In the Netherlands (and most of Europe), you would write one thousand > million watts as 1.000 megawatts. > > The decimal indicator in Europe is a comma. > For example, > 1,5 means one and a half > 1.000.000 means one million. > > Sil > (ex PA3HIL) Hi Sil, ZL2CIA In Italy you would write one thousand million watt as 1000 megawatt or alternatively 1000 MW In addition the units in Italy are written without plural and to write megawatts is wrong in Italy but the plural is used in England and USA In any calculator 1.5 means one and half because the calculators are not using comma. In any calculator 1000000. means one million I thing that the best for everybody should be to write numbars as any calculator shows. 73" de i8CVS Domenico

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