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> SAMI 2.6 m Tri-Star C/Ku Band Antenna
SAMI 2.6 Meter Tri-Star Dual C/Ku Band Antenna
This is the primary antenna I use for general
reception. Considering that I live in West Virginia, and there used to
be a joke about the C-band dish being West Virginia's state flower,
these things are pretty plentiful. I got this one for free after I put
an ad in the paper. Of the three large alumium mesh dishes I own, this
is the best.
This dish was
manufactured in 1994. When I first got it,
it was actually in pretty good shape, requiring only minimal attention.
The mesh panels are totally free of dents and holes, and are made of
the fine screen that allows good reception of both C and Ku band. Some
older antennas have a coarser screen that doesn't work as well at short
wavelengths. Another desirable feature is the tripod feed support,
which is more stable and easier to adjust than the monopole type.
It originally came with a Venture actuator motor with
36" of travel, but I swapped it out for a VonWeise motor with one meter of
travel, a higher count sensor, and quieter operation. You could
actually hear the Venture actuator and it sounded like a can opener,
whereas the VonWeise is totally silent. The swivel bearing on the end
of the actuator arm was frozen up with rust and would not move at all,
but a combination of soaking it overnight in WD-40 and exercising it
back and forth it with a metal bar broke it loose. There's no grease
fitting, but I packed as much grease as I could into that bearing. It's
probably a good idea to re-lube it a couple of times a year.
There were only a few small parts in need of repainting.
To make everything look new I went ahead and stripped the steel parts
like the polar mount and the feed support legs and repainted them with
some black satin Rustoleum. I didn't really need to, but I replaced
most of the hardware as well.
Finding a good site for a motorized dish is harder than
finding a site for a fixed dish, since you need a clear line of sight
to all of the orbital locations, or at least as many as possible. I
used an inclinometer to double check, but since I live on a high ridge
without any tall trees close by I have a perfectly clear LOS from
horizon to horizon pretty much anywhere in my yard. I eventually
settled on a nice spot in my side yard, about 20 feet from the house.
The closer you can get it to the receiver the better.
Assembly and Mounting
So, the most common way to install one of these things
is on a post/pedestal set into the ground. The best type of pipe would
be a 3" OD galvanized steel electrical conduit. For a dish this size
the hole should be at least two feet deep, about 18 inches around, and
should get bigger towards the bottom. The post should have at least a
couple of lag screws or bolts driven into it near the bottom of the
hole, to keep it from turning. Next step is to fill the hole with
concrete. I think I used about 400 pounds, keeping in mind that it's
better to use too much than not enough. I also built a little concrete
pedestal around the base of the post to give it some extra support,
using a 5 gallon bucket as a form, and filled the pole with concrete
for good measure. After pouring the concrete and leveling everything up
I left it for a few days, by the time everything hardened up it was
completely rock solid - no give whatsoever no matter how hard you
pulled on it.
I set the polar
mount on first. The actuator went on
next, just to keep everything from flopping around
while I was working on it. The part that attches to the polar mount has
a clamp that goes around the barrel of the actuator, so that you can
adjust it. I set this so that with the actuator fully retracted the
dish would be pointed West of AMC 10, the most Westward satellite
visible from my earth station. Now would be a good time to check the
elevation settings. This was a used dish that I got locally, so I knew
it wouldn't be too far off. To do this, swing the polar mount to it's
highest position, then check the elevation with a protractor. The angle
you get should be the same as a satellite located at your longitude.
For example, my longitude is 80°W, a satellite located at 80°W
would have an elevation of 45°, so I set my polar mount's elevation
at 45°. According to my protractor it was only about a degree or so
Now I assembled the reflector which comes in three wedge
shaped sections that fasten together with a few dozen bolts. Matching
it up with the polar mount was not easy. It doesn't weigh very much,
but its large and unwieldy, so it's kind of hard to orient it right and
steer it so that the support ribs rest in the three little holders.
This is one of those things where it helps to have two or three people.
Now, the polar mount needs to be aligned as close to true North-South as possible. I
used a compass, but there's a few things you need to know about
compasses before you do this yourself. A compass points to magnetic North, which is a few
thousand miles away from true North.
The difference, called declination, depends on where you are, but it
can be between 0 and 20°. The US Naval Observatory and NOAA has a
resources to help with this. At my site, declination is 8°W,
which means that a compass bearing of 188° is true South. You'll also want to
keep the compass at least a couple of meters away from anything metal,
so don't like hold it right up to the side of the polar mount.
Now for the most
important part: the feed assembly. When
I got this dish it came with a Channel Master servo motor type
feedhorn, with an Eagle Aspen LNB. This type of feed uses a servo motor
to physically rotate a dipole antenna inside the feedhorn to select
either H or V. Since most modern digital receivers don't support servo
motor feeds, I subbed in a dual band C/Ku LNBF from Eagle Aspen. This
feed can receive both polarities for both C and Ku with a single
device. There are two separate outputs, which can be combined into a
single cable with a DiSEqC switch, polarity control is via line
voltage, like any other dual polarity LNBF.
I thought about making a device that controls the
polarity of a servo motor feedhorn based on line voltage. It's a pretty
simple concept. With a servo motor feed, there are three wires going to
the motor, +5V, ground, and pulse. The receiver sends a square wave of
one frequency down the pulse line for H and a different frequency for
V, so all we'd really need is two oscillators and a voltage controlled
switch. A Chaparral servo motor I tested was comfortable with 57.26 Hz
for one polarity and 58.38 for 90° of rotation. I was pretty
surprised to learn that someone beat me to it, and such a device can be
purchased from Rick's Satellite.
The cool thing about a device like this is that it lets
you use a high performance feedhorn assembly, rather than the really
cheap C band LNBFs so common today.
I went out and got the best dual band feedhorn ever, the
Corotor II Plus, which can be purchased online from the factory. I
can't remember where I put the Eagle Aspen LNB that originally came
with this dish, so I used a very nice CalAmp (from back when they still
went by California Amplifier) MAG-90 LNB, circa 1993, with a 40°
noise temperature. I had a lot of Ku band LNBs laying around, mostly
Dish Pro LNBs off of Super Dishes. I eventually settled on one of those
NJR LNBs that look like a soda can, which came off of an old Primestar
dish. I would eventually swap it out with the very old Norsat 9000A LNB
that came with my mysterious Ku band
dish of unknown origin.
On this type of
dish, the scalar ring is what holds
everything together. The easiest way I've found to do this is to tilt
the dish as low as it will go, then attach the feed support legs to the
dish, then bolt on the scalar
ring. Now's a good time to check that the "bore sight" of the scalar
ring is pointing directly at the center of the dish. You can eyeball
it, but the best way is to use a laser pointer.
The Corotor II+ comes with a template that fits on to
the Ku band waveguide with an arrow that should be aligned to the polar
axis of the dish. With the dish at its highest elevation, this would be
straight up and down. For an LNBF there will be an arrow engraved into
the feed that should be aligned to the dish's polar axis. You can fine
tune it later with a signal meter.
There are markings, usually from 0.20 to 0.50 engraved
on the side of the feedhorn. This is where you set the F/D ratio that
determines how the dish is illuminated. Lower F/D ratios are used for
antennas with deep reflectors, and higher ratios for shallow
reflectors. If you can find the manual for your antenna, it should give
the F/D ratio. If not, you'll have to calculate it yourself.
I have an Applied Instruments Super Sat Buddy signal
meter, which comes preprogrammed with all of the satellites and
transponders in both bands, and can supply power to the LNB an operate
a wide variety of switches, but costs around $600. A cheaper model in
the under $200 price range like the Sat Buddy or one of the First
Strike meters would be a good choice also. The little analog signal
meters work surprisingly well and are widely available for under $25.
If you don't want to spend the money on a signal meter, a satellite
receiver will work, but not as well as the cheap little $20 analog
This might not be the best way, but this is how I did
it. The lowest satellite I can receive is AMC 10 at 135°W, I used
the motor to move the dish West until the elevation, as measured by a
protractor in the center of the dish, matched the elevation of AMC 10:
18°. Now I sweep the dish back and forth on its post looking for
the strongest signal, then tighten up the bolts. Now I moved it to the
elevation of the satellite closest to the zenith, in my case this is
SES 2 at 87°W with an elevation of 43°. I marked the position
on the pole, then repeated the East-West sweep. If the strongest signal
at the highest satellite is the same position as the lowest satellite,
then everything is lined up properly, tighten all of the bolts firmly;
I used a wheel wrench for this.
The cabling for a motorized dish like this is special.
It uses a ribbon
cable with two coaxial lines, one four conductor cable for the motor,
and one three conductor cable for the polarity motor. Commscope is the
only company I know of that still makes this, but it's expensive, and
the only place I know of that sells it is Rick's
In a pinch, you can use regular coaxial cable, along
with the low
voltage cable usually used for landscape lighting for the motor power,
and phone or network cable for the motor sensor and polarity motor. I
lucked out and found about 30 feet of it rolled up inside the ceiling
of a golf course where I was installing a satellite system. The owner
let me have for free, but it smells like hot dogs since it was right
above the kitchen.
All of the coaxial
cables for this dish have PCT
one piece nickel plated brass compression connectors, which I prefer over other brands
for two reasons, one: no plastic parts to disintegrate with exposure to
sunlight, and two: a nitrile sealing washer to help keep moisture out.
For good measure I always squirt in a little silicone grease before I
torque them to 22 in-lbs.
The other wires need sealing treatment too, I used those
silicone filled Scotch
Lock connectors commonly used on telephone
for the motor sensor and servo control, and silicone filled wire nuts
for the motor power. All of the junctions are housed inside a
weatherproof plastic box, which has a grounding block connected to the
main grounding rod via a heavy, 10 gauge wire.
The new Chaparral Corotor II+ with its MAG-90 and Primestar LNBs
A view inside of a servo motor type feedhorn.
The CalAmp MAG-90 C band LNB I'm currently using. It's over 20 years
old, but seems to work quite well, even with 8PSK HD broadcasts.
The original feed and LNB that came with this dish.
The original location of this dish.