Reading the AO51 book by Gould where he discuses the L band requirements. For occasional contact 150 W EIRP is needed. For superior performance 1 Kw EIRP needed. Assuming I start out with 10W to a 16 turn helix 40 feet away. Guesstimating 58 W at the antenna, helix gain 812db. Guestimated EIRP about 40W (worst case). Am I figuring this correct? If so then AO51 is performing better than what the book says. I am trying to "fine tune" what I have.
Thanks 73 Bob W7LRD
Seattle
Hi Bob,
As noted in the book, Mike Seguin, N1JEZ did those measurements during the first few months after launch. They proved to be pretty close as I remember. Mike noted that he was able to hold the L band uplink with 50W EIRPc, after he had fine tuned his antenna and carefully adjusted his Doppler to the center of the capture window. Once people found the uplink frequency sweet spot for their TX and used auto Doppler, things also improved. We also tweaked the audio level into the trasmitter over time to improve the transmit audio from the satellite.
But in year six, it is probably a good time to get some new measurements.
73, Gould, WA4SXM
 Original Message  From: "Bob W7LRD" w7lrd@comcast.net To: amsatbb@amsat.org Sent: Tuesday, April 27, 2010 2:40 PM Subject: [amsatbb] AO51 L band requirements
Reading the AO51 book by Gould where he discuses the L band requirements. For occasional contact 150 W EIRP is needed. For superior performance 1 Kw EIRP needed. Assuming I start out with 10W to a 16 turn helix 40 feet away. Guesstimating 58 W at the antenna, helix gain 812db. Guestimated EIRP about 40W (worst case). Am I figuring this correct? If so then AO51 is performing better than what the book says. I am trying to "fine tune" what I have.
Thanks 73 Bob W7LRD
Seattle _______________________________________________ Sent via AMSATBB@amsat.org. Opinions expressed are those of the author. Not an AMSATNA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsatbb
 Original Message  From: "Bob W7LRD" w7lrd@comcast.net To: amsatbb@amsat.org Sent: Tuesday, April 27, 2010 8:40 PM Subject: [amsatbb] AO51 L band requirements
Reading the AO51 book by Gould where he discuses the L band requirements. For occasional contact 150 W EIRP is needed. For superior performance 1 Kw EIRP needed. Assuming I start out with 10W to a 16 turn helix 40 feet away.Guesstimating 58 W at the antenna, helix gain 812db. Guestimated EIRP about 40W (worst case). Am I figuring this correct? If so then AO51 is performing better than what the book says. I am trying to "fine tune" what I have.
Thanks 73 Bob W7LRD
Seattle
Hi Bob ,W7LRD
The gain of a 16 turn helix is much more than 8  10 dBi .Supposing that the circunference of a turn = Lambda or one wavelenght = 23 cm and the pich angle between turns is Alpha = 12.5 ° then the halfpower beamwidth can be calculated using the following formula from Kraus book "ANTENNAS" Halfpower beamwidth = 52° / SQR ( n x tan alpha ) where n= numbar of turns and so for 16 turns helix we have:
Half power beamwidth = 52° / SQR ( 16 x tan 12.5° ) = 27.6°
An antenna having a lobe large as 27.6° at the 3dB points in 1268 MHz is corresponding to a parabolic dish with 70 cm in diameter and has a gain of 16 dBi corresponding to 40 time in power ratio.
If the power reaching your 16 turns helix antenna is only 5 watt then your EIRP=5 x 40=200 watt and if the power is 8 watt your EIRP= 8x40=320 watt
It seems that the book by Gould is correct.
73" de
i8CVS Domenico
participants (3)

Bob W7LRD

Gould Smith

i8cvs