Re: Arecibo on 432 MHz Moon Bounce (some calculations)
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@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@hotmail.com ======================================
At 07:46 AM 4/22/2010, Edward Cole wrote:
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@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
hmm dBi = dBd +2.15. Gain of dipole = 1.64 10Log(1.64) = 2.15 dB so what gives here? is it 58 dBd and 60 dBi? Sorry if I wrote that backwards. Or we just playing around with significant numbers and gain is approx 58 to 60 dB (somethings).
Pat, Joe? can you please clear up this mess and state for everyone what the gain is for Arecibo on 432-MHz?
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@hotmail.com ======================================
----- Original Message ----- From: "Edward Cole" kl7uw@acsalaska.net To: w3hf@arrl.net; amsat-bb@amsat.org Sent: Thursday, April 22, 2010 5:46 PM Subject: [amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations)
Hi Ed, KL7UW
You writes:
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)
73, Ed - KL7UW, WD2XSH/45
Ed , you have reversed dBi with dBd
58 dBi cannot be converted to 60 dBd because the gain of a dipole over the isotropic antenna is 2.14 dB then 60 dBd is corresponding to 60 + 2.14 = 62.14 dBi
By the way 58 dBd is corresponding to 60.14 dBi rounded to 60 dBi wich is the official gain given for Arecibo at 432 MHz
73" de
i8CVS Domenico
dBi is used in range calculations because a isotropic antenna has an even radiating field leaving only distance as a variable when calculating path loss. After determining the path loss for a given distance, the antenna gain, transmit power, receiver sensitivity, receiver noise, cable loss, and connector losses are factored into the equation to give a link budget. With the excess allocated to fade margin. ERP calculations are used by regulatory agency's to determine possible interference.
Art, KC6UQH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Edward Cole Sent: Thursday, April 22, 2010 8:47 AM To: w3hf@arrl.net; amsat-bb@amsat.org Subject: [amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations)
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@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@hotmail.com ======================================
_______________________________________________ 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
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participants (3)
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Art McBride -
Edward Cole -
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