[amsat-bb] Re: Help for Humber College Students with ISS Contact
Alan
ve4yz at mts.net
Wed Nov 26 18:16:27 PST 2008
With all due respect to describing LHCP and RHCP which gives me a brain
crap... Here is a visualization of polarization.
http://sv1bsx.50webs.com/antenna-pol/polarization.html
... Alan
-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Roger Kolakowski
Sent: November 26, 2008 5:38 PM
To: AJ9N at aol.com; gordonjcp at gjcp.net; amsat-bb at amsat.org;
paul_je at hotmail.com
Subject: [amsat-bb] Re: Help for Humber College Students with ISS Contact
Nice explanation...Thank you!
Roger
WA1KAT
----- Original Message -----
From: <AJ9N at aol.com>
To: <gordonjcp at gjcp.net>; <amsat-bb at amsat.org>; <paul_je at 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 at gjcp.net writes:
>
> Ken Owen wrote:
> <snip>
> > From: Paul Je [mailto:paul_je at 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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