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Re: Help for Humber College Students with ISS Contact



Nice explanation...Thank you!

Roger
WA1KAT

----- Original Message -----
From: <AJ9N@aol.com>
To: <gordonjcp@gjcp.net>; <amsat-bb@amsat.org>; <paul_je@hotmail.com>
Sent: Wednesday, November 26, 2008 11:04 AM
Subject: [amsat-bb] Re: Help for Humber College Students with ISS Contact


> Hi all,
>
> Let me clear up a little bit of what ARISS wants for a school ground
> station.  What you do for your own home contact is your business but here
is what we
> want for an ARISS school contact:
>
> 1.  We require two complete radio stations, each one 75 watt  class or
better
> (we actually prefer over 100).  RF amps are OK.  The  radios should have
the
> ability to go in frequency steps smaller than 5kHz so  that the Doppler
shift
> can be corrected (at 2 meters it goes about +/-3.5  kHz).
> 2.  The primary radio is to have a circular polarized beam with  azimuth
and
> elevation control rotors.  We prefer computer control of the  rotors.
> 3.  The backup radio is to have a vertical and/or eggbeater style
antennas.
>
> Now for a short explanation of why for each:
>
> 1.  The need for two complete radios is so that if one radio fails for
any
> reason, the school contact can carry on (it is recommended each radio be
on
> its own 120VAC circuit and UPS if possible).  The reason for the 75  watt
class
> is that we want to have as much signal to reach the ISS as  possible.  The
ISS
> is actually pretty noisy and the radio footprint is very  big and it picks
up
> all sorts of interference.  So it helps to have as much  signal get to the
> astronaut.  Throw in the fact that the ISS superstructure  is so big now
that we
> have had schools have the signal dropout to almost nothing  and you can
see
> that every little bit helps.
>
> 2.  The circular polarized beam helps because the signal to and from  the
ISS
> can be bouncing off of the superstructure itself and in some cases the
> surrounding ground terrain.  As I mentioned above, we have had some
schools  where
> the signal dropped out almost to zero.  Luckily the signal (sometimes
about a
> minute later) came back up as the ISS changed its orbital position
relative
> to the ground station and thus some of the blockage was reduced.   I have
done
> 4 school contacts as control op and I use 5x2  LHCP and 10x2 RHCP circular
> polarized beams with an antenna  switch.  Most of the ARISS telebridge
stations
> are using something  similar.  The ISS antennas are basically vertical
> antennas but the signal  can be deflected all over the place because of
the
> superstructure.   I tend to run my contact on the RHCP beam (but  I am
ready to
> switch) but we at ARISS have had some reports where the signal did  come
up a bit
> when using LHCP. Those who are really into satellite work know  that the
RF
> pattern does change during a contact so it makes sense to be able to
switch
> polarity.  And don't forget the ISS radio is running maybe 25 watts  (or
maybe 5
> depending on the radio used) and can not do any Doppler  correction.
>
> 3.  The backup radio is to have a non-directional antenna so that in  case
of
> rotor or computer failure, the contact can carry on although it will be
with
> a shortened contact time and the quality may suffer.  I have an  antenna
> switch to switch between the 2 antennas during a pass as the RF pattern
between
> the 2 antennas is completely different.
>
> The biggest reason for doing what some may think is overkill is this.
The
> hams involved with a school contact are just the messengers.  The  school
kids,
> teachers, and parents are the ones we have to satisfy and they  don't
> understand this ham radio business.  They do understand good audio  and no
screw ups
> on the part of the ham crew.  I always tell the schools  that I mentor to
plan
> on 600 to 800 people-hours for 10 minutes of contact  time.  They usually
> think I am nuts until they do the contact and they  often tell me that my
> estimate was too low.  Think of a school contact as  your worst case Field
Day; not
> so much because of the equipment issues but  because of the 600 or so kids
> watching.
>
> Hope this helps a little.
>
> 73,
> Charlie Sufana AJ9N
> One of the ARISS mentors
>
>
>
> In a message dated 11/26/2008 4:15:52 A.M. Central Standard Time,
> gordonjcp@gjcp.net writes:
>
> Ken Owen  wrote:
> <snip>
> > From: Paul Je [mailto:paul_je@hotmail.com]
> > Sent: Monday, November 24, 2008 1:17 PM
> > To: Ken Owen
> >  Subject: RE: ISS contact
> >
> > Say Ken, we've set up our primary  station just fine, but I was
wondering if
> > I could ask for your  advice.  Well, you see, we've tested the
transceiver
> > that we have  (the ICOM IC-V8000), and we can transmit and receive just
fine
> > with it  on our circular-polarized HyGain 2m antenna.  Also, we did a
VSWR
>
> What kind of antenna?  Anything more than a 3-element Yagi  will be more
> trouble than it's worth.  Bear in mind that I've  successfully sent and
> received APRS with the ISS using a homebrew  vertical.  The higher the
> gain of your Yagi, the more directional it  is, and the more accurately
> it needs to be pointed.  I find that a  3-element beam is okay for
> handheld use when working portable, and has  more than enough gain to hit
> the amateur satellites with 5W from an  HT.
>
> > test and our loss is minimal with the 75W transceiver that the  ICOM
>
> 75W sounds a bit much, especially into a very directional antenna.
> You're trying to talk to the ISS, not etch your name on the  side.
>
> > produces.  Ok, so here's the problem.  Even with  all the proper testing
> > done, we still can't seem to pick up or hear  the 166MHz beacon that the
ISS
> > produces.
>
> Are you using a 166MHz  aerial for this?  Are you sure the beacon is even
> transmitting when  you think it is?  Your high gain Yagi might well be
> very very deaf  outside its intended band.  Try making a simple dipole or
> even a  two-element beam for 166MHz.  With two elements, it will have a
> more-or-less cardioid pattern, so you shouldn't really even need to
> steer it much ;-)
>
> > My classmates and I are a bit  worried/stressed out.  I mean, just on
last
> > Friday, we did a test  and someone drove at least 5km away from out
college
> > and heard us fine  with the handheld radio he had.  We had a signal
strength
> > of 3+  out of 5.  He could've drove out even further, but we felt that
we
> did
> > enough testing to know that any attenuation losses were very  minimal.
>
> The ISS is pretty much the classic case of  line-of-sight.  There's
> nothing in the way, and it's only 200 miles  away.  There's nothing to
> stop the signal anywhere.
>
> > Well,  do you know what the problem could be?  Have you heard the
beacon?
> > What does it sound like?  Maybe we should delay or  advance the rotor by
a
> > few seconds?   We're using NOVA  software, and it allows us to send our
> > transmission a few seconds  ahead or behind.
>
> Use a wider beamwidth.
>
> > Ok, so we  have a circular polarized HyGain antenna hooked up to our
Yaesu
> >  G5500.  Uhm, this might sound dumb but do you know whether we should
be
> > right hand circular polarized or left hand circular  polarized?  Is the
ISS
> > right hand or left hand on  144.490MHz?
>
> This I'm not sure about.  I thought about  building a circular polarised
> antenna for ISS and amateur satellite work,  but it seemed more trouble
> than it was worth.  If you've got the  polarisation wrong, it will be
> incredibly deaf!
>
> > I'm trying to  research this, but I'm having the hardest time to find
this
> >  information out.  Oh, also, since our antenna is circular-polarized,
does
> > the way we set our antenna have an effect on our  transmission?  I know
this
> > sounds confusing, but let me  explain:
> >
> > If you looked at our antenna from the front so  that you could see all
the
> > dipoles/elements both vertically and  horizontally to your view, well,
> should
> > they be perfectly aligned with  one set horizontal and one vertical?
Both
> > the vertical and the  horizontal are perfectly 90degrees to each other,
> > however, instead of  being a perfect cross to your view, the elements
are
> > more like an "X"  to your point of view (even though both are perfectly
> > 90degrees to  each other).
>
> That shouldn't make much of a difference.  Imagine  the signal arriving
> like a big corkscrew - the key to the circular  polarisation is that the
> signal arrives at one set of elements and then a  quarter wavelength
> later arrives at the second.  Now, let's imagine  we've made our
> circular-polarised aerial by putting two dipoles on a boom,  1/4
> wavelength apart, and connected them by two equal-length lines.   The
> vertical one is at the "front" of the boom and the horizontal one is  to
> the "back", and the up and left elements of the dipoles are  "hot".
>
> Let's pause reality just as a "vertical" peak hits the vertical  dipole.
> That dipole now has some signal.  Using the  single-Planck-time advance
> button on our Worldivo (it's like a Tivo for  the fundamental nature of
> the Universe), we'll step through - tick, tick,  tick, tick - until a
> quarter wavelength has passed.  Now the vertical  peak is somewhere above
> the centre of the horizontal dipole - it's picking  up no signal - and
> there's a horizontal peak about the centre of the  vertical dipole - no
> signal there either.
>
> Step forwards another  quarter wave, and there's a vertical dip at the
> cold end of the vertical  antenna, and the horizontal peak we just saw
> came in is at the hot end on  the horizontal antenna.  We now have a
> negative signal on the cold  side of the antenna connection (remember,
> both dipoles are effectively in  parallel) and a positive signal on the
> hot side of the antenna connection  - loads of signal!
>
> If we reversed the direction of the corkscrew, or  reversed the phase of
> *one* of the dipoles, then the two signals would  cancel out almost
> completely.  You can have two signals transmitted  in left and right
> circular polarisation on the same frequency, and have  *phenomenal*
> rejection between the two.
>
> I should point out that  there's quite a lot in that explanation that's
> not entirely true, or at  least terribly inaccurate.  It's still a useful
> model for getting  your head around what seems at first to be a very
> confusing polarisation  mode.
>
> HTH,
> Gordon
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