Hi Bob, WB4APR I suggest you to take a look at the succesful 20 MHz and 40 MHz HF antennas used by SPUTNIK-1
http://www.antenna-theory.com/phpbb2/viewtopic.php?p=451&sid=e909b07b8e95c79 ac9a04a6adec04932 The 58 cm sphere had four antennas, two were 2.4 meters long and two were 2.9 meters long. They were V shaped turnstile angled at 35 degrees from the longitudinal axis, and two transmitters alternately emitted 20 or 40 MHz. Following your proposal a deployed 1000m tether have a very poor radiation efficiency and will have so much drag and the Cubesat will de-orbit in only a few days On the other side the V shaped turnstile are very short and your Cubesat experiment will not be limited by the drag factor and will last a very long time . Also take a look at the HF antennas of OSCAR-6, OSCAR-7, RS-10/11, RS-12/13, RS-15 and RS-16 73" de i8CVS Domenico ----- Original Message ----- From: "Bob Bruninga" <[email protected]> To: "'James Duffey'" <[email protected]> Cc: "'amsat-bb BB'" <[email protected]> Sent: Wednesday, April 20, 2011 8:41 PM Subject: [amsat-bb] Re: HF Satellite Experiment? (hi Z) > Subject: Re: [amsat-bb] HF Satellite Experiment? > > > Bob - Calculate the resistance of 1000M of whatever > > wire you are using at the frequencies you are operating on. > > It will be low. The resistive component of the impedance > > will dominate the reactive component, so a simple > > transformer will do. > > Turns out I just learned today that the tether is going to be about 2k ohms. > That's 2 ohms per meter or Huge! For the first half wavelength at 7 MHz, > this is 40 ohms or a nice dummy load... > > Putting that into EZNEC changes the antenna from the expected long-wire cone > with 14 dBi gain straight down to a nearly perfect Dipole pattern (off the > sides) with a gain of - 64 dBi and a feed point impedance of 50000 +j36000. > In other words, only the first 1/2 wave is really doing anything as far as > pattern. > > Again, these are only 1st cut assessments(we haven't really modeled the > actual cubesat structure yet), but this high resistance of the tether is > really going to need some looking at... > > Bob, WB4APR > > > Cubesat HF experiment: > > > > > > > > We have revised our HF satellite experiment proposal to be a CW telemetry > > beacon on 40, 20, 15 and 10 meter bands. The experiment will last only a > > few days, since the deployed 1000m tether will have so much drag, we will > > de-orbit in only a few days. > > > > > > > > The idea is a keyed CW oscillator on 7.010 MHz with harmonics on 14.020, > > 21.030 and 28.040 MHz. These bands are all in the IARU Satelilte > > allocation. We will filter all harmonics above 28 MHz. > > > > > > > > The challenge will be how to feed a 1000m long wire from only a 4"x4"x7" > > counterpoise (on all bands). transformer coupling? > > > > > > > > The tether will be vertical and can act as a long wire antenna with a very > > narrow cone angle pointed straight down. Antenna gain will be more than > 10 > > dB on all bands. This moving donut gain pattern sweeping across the earth > > should pose some interesting reception reports (If any of it gets through > > the ionosphere). > > > > > > > > Launch Opportunity no earlier than March 2012. Putting us closer and > closer > > to the Solar Max which would be the worst time for this experiment. > > > > > > > > Other than a nice AMSAT experiment, if anyone can use this for valid > > ionosphereic science, come join us. > > > > > > > > Bob, WB4APR > > > > > > > > > > > > > > > > _______________________________________________ > > 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 > > -- > KK6MC > James Duffey > Cedar Crest NM > > > > > > > _______________________________________________ > 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 _______________________________________________ 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
