----- Original Message ----- From: "Bob- W7LRD" <[email protected]> To: <[email protected]> Sent: Tuesday, April 27, 2010 8:40 PM Subject: [amsat-bb] AO-51 L band requirements > > > Reading the AO-51 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- 5-8 W at the antenna, helix gain 8-12db. Guestimated > EIRP about 40W (worst case). Am I figuring this correct? If so then AO-51 > 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 half-power beamwidth can be calculated using the following formula from Kraus book "ANTENNAS" Half-power 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 _______________________________________________ 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
