[amsat-bb] Re: HF Satellite Experiment? (hi Z)
domenico.i8cvs at tin.it
Wed Apr 20 17:26:08 PDT 2011
Hi Bob, WB4APR
I suggest you to take a look at the succesful 20 MHz and 40 MHz
HF antennas used by SPUTNIK-1
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
Also take a look at the HF antennas of OSCAR-6, OSCAR-7, RS-10/11,
RS-12/13, RS-15 and RS-16
----- Original Message -----
From: "Bob Bruninga" <bruninga at usna.edu>
To: "'James Duffey'" <jamesduffey at comcast.net>
Cc: "'amsat-bb BB'" <amsat-bb at amsat.org>
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
> 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
> 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
> In other words, only the first 1/2 wave is really doing anything as far as
> 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
> > beacon on 40, 20, 15 and 10 meter bands. The experiment will last only
> > few days, since the deployed 1000m tether will have so much drag, we
> > 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
> > narrow cone angle pointed straight down. Antenna gain will be more than
> > dB on all bands. This moving donut gain pattern sweeping across the
> > should pose some interesting reception reports (If any of it gets
> > the ionosphere).
> > Launch Opportunity no earlier than March 2012. Putting us closer and
> > 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
> > _______________________________________________
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> James Duffey
> Cedar Crest NM
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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