Drew Draws A Crowd
Speaking to a captivated audience, Drew presented the the history and theory behind satellite communication. Later the group retired to the outdoors where he put theory into practice. In the space of a few minutes he made a contact with a ham in Texas.Then, wishing to share the fun Drew got Liam KM4STS to participate.
Liam KM4STS makes the call while Drew aims the antenna.
Liam takes his turn holding the antenna while
Tyler takes the mic,
and Liam's mom, dad and grandpa, all hams, look on.
They make it look so simple. Like child's play. :-)
In his presentation
Drew discussed the history, theory, and practice of ham radio
satellite communication. It was made clear that it doesn’t take
much to get started in satellite radio. An antenna and a dual band HT
will do. Two dual bands are better.
For those
interested, the Internet is a great place to start learning about
this phase of ham radio. Besides the radio you will need a
directional antenna and some idea of where the satellite you are
trying to reach is at any moment. Antennas can be purchased, or if
you prefer, you can build your own. The two popular brands are the
Elk and the Arrow. Both are priced in the $145 dollar range. This is
a lot of money if you just want to experiment to see if you might be
interested in this phase of the hobby. For the cost conscious, the
tape measure beam optimized for direction finding might be just the
ticket.
So assuming you have
the radio/s and a suitable antenna, how do you determine the
direction to point the antenna and the frequency to set your radio?
The pointing
solution comes from software programs which use unclassified
information collected by NORAD and passed onto NASA. From this data,
these programs predict the position of the satellites at any one
time. Using software like this lets you know when the satellite is in
range.
Most of us are
familiar with repeaters and how they rebroadcast an incoming signal
either above or below the received frequency. However, with
satellites, the operation is somewhat different. Most satellite
transponders, repeat what they hear, the up-link signal, on a another
band, the down-link signal. There is another wrinkle. Because the
satellite is moving it will exhibit a Doppler shift. This means that
as the satellite rises its frequency will appear to be higher than
published, and then once it has reached its peak, will become
progressively lower than published. This shift is more pronounced on
the higher frequencies.
Mode describes the
up-link and down-link bands used. For example Mode V/U means the
up-link is on VHF, and the down-link on UHF. Mode U/V would be the
reverse.
Schedule is another
important piece of information to have. Satellites are not always on.
However, schedules are published for each. It is a good idea to
check ahead of time.
This link will get
you started:
Click on the above link. This will take you to the AMSAT site.
Start by clicking on
the drop down menu Satellite Info
Scroll down to
Communications Satellites
Pick one, ie AO-85
Read about its
history and discover the frequencies it operates on.
Go back to the drop
down menu Satellite Info
This time select
Pass Predictions
Select the Satellite
of interest AO-85
Enter your location
grid square or latitude and longitude
Click on Predict and
a table similar to the following will appear.
To interpret this
chart you need to know the following:
AOS (UTC) stands for
Acquisition Of Signal in Greenwich Mean Time – the time the
satellite just pops over your horizon
AOS Azimuth – the
location of the satellite in relation to true north as it just pops
over your horizon.
Maximum Elevation is
the maximum height of the satellite above the horizon in degrees.
Max EL Azimuth is
the direction relative to true North when the satellite is at its
highest point on the horizon relative to your position.
LOS Azimuth stands
for the direction relative to true north when the signal will be
lost.
LOS(UTC) is the
Greenwich Mean time the signal will be lost.
So on May 6, at
14:54:36 AO-85 just popped over the horizon for someone living in
Lakeland. The direction was 226 degrees from North. After about 5
minutes the satellite reached a height of 32 degrees above the
horizon at a direction of 311 degrees from North. Finally, the
satellite disappeared over the horizon about five minutes later at a
direction 15 degrees from North.
Finally, by clicking
on View the current location of AO-85 you can get a plot of where it
is and where it is expected to be in the near future.
If this information
gets you interested in satellite communications, it has done its job.
Several of our club members are heavily involved with this mode of
operation. Two in particular are Matthew KK4FEM and Rich N4ESS. I am
sure they would be happy to share their experiences with you.
Note: after reading this post Matthew made some valuable suggestions.They follow:
Hi bill,
I read your blog post. If I may offer a few suggestions...
You don't have to pay $145 for an arrow. The least expensive one they offer
will work fine with 2 radios (it doesn't include a duplexer) for $90. Also, if
you purchase any of these things through the amsat store, they get a percentage
of the sales to support operating and building more satellites.
We also highly recommend AGAINST using tape measure Yagis for sats. These
may have worked fine in the past for birds with stronger down links, but with
the current fleet of sats people will just be frustrated trying to use them.
They don't have enough gain, especially on 70cm to allow people to copy the
downlink effectively.
A much better alternative if folks don't want to shell out the cash for an
Arrow or Elk is the WA5VJB "cheap yagi" that drew mentioned during his
presentation. This can be built using scrap wood and common house wire for
almost no money. Here is the info.
