A 2 Meter (145.990 MHz) Patch for Suitsat
I store surfing one day at the local Home Depot and I noticed something that had definite antenna possibilites - 2" thick 4' x 8' sheets of styrofoam with aluminum foil on both sides. Now I live in a solar heated house, and it has this on the sides for more insulation beneath the siding, so it was nothing entirely new to me, but here was a new antenna source I had not thought of before! I have been making patches for several years on 435 MHz through 2.4 GHz, but they always used aluminum or brass (or soup can lids) sheets for the reflector and patches. So I bought several sheets for 23 each and brought them home. I figured that the price was right and I could cut them out with a kitchen knife if the XYL wsn't looking. Unless I got fancy, one sheet should handle two 2 Meter patches.
The 1st version was simple a scale up (in size) from the 435 MHz patch that I used to feed my dishes (found in the triband patch feed secton of this webage.) It was made from 1/2" foil faced foam with about 3 iinches between the circles. It did no resonate well and the circularity was non-existent.
"No tune 2M patch for Receiving Suitsat
( makes a great 2M antenna)
Material: 4' x 8' x 2" thick double aluminum
foil faced styrofoam (makes two antennae) $23 @ Home Depot
Six 4" x 4" wide squares osf 1/8" (not critical) aluminum
Two with 3/8" hole in center for mounting
patch
Two with ~ 1/2" holes in center for mounting
SO-239 in each
.
Two with 3/16" holes in center for attaching
bolt center conductor extension
Two SO-239 (or Type N) connectors with a 2 1/2" long 10-24 brass bolt with the
head cut off soldered to the center conductors. (and two 10-24 nuts).
Eight 1/2" long 4-40 bolts for mounting the SO-239s to the centers
of two plates.
12" long 3/8" nylon bolt for attaching patch system to mount w/o shorting center
conductor to patch. Steel threaded rod OK too but shorts
the reflector and patch together..
Cutting the Foam:
Cut the foam into two 4' by 4' pieces.
Drill a 3/8" hole in the center. mount the 3/8" bolt
Make a 48" circle. A serated utility knife is marginal (blade too short),
a hunting knife is better I usually use a Stanley "Fat Max" knife, but
it sure makes a mess
Best way: I cut the 48" circle is to mount the center bolt in a table, and 24"
from a bandsaw and spin the foam as the bandsaw makes a perfect circle.
But this circle is not particularly critical so any method will do fine.
One side of the foam usually has more foil damage than the other, so make the
better side the patch.
Cut the patch side by removing the outer foil to achieve a 42 7/8" circle
at the center. I make a circle cutter out of a 24" piece of some stiff
material with a 3/8" hole in one end and a new #11 XACTO blade exactly 21 7/16"
out from center protruding downwards 1/4" and backwards ( to cut, not tear)
Mount it on the center bolt; spin it around and you have a near perfect cirecle..
The toughest job is removing the outer unused aluminum foil that is glued quite
well to the surface. I can pick it off but this can take hours.
A better way is to sparingly and quickly using a heat gun to losen the glue
ahead as you pull it off. Put some metal, or cardboard or something with
part of a 42 7/8" circle cutout, as a heat shield, over the patch to avoid losening
its glue/or forming airbubbles. in the patch. But if you do have some
whopsies, they really won't hurt anything, they just look ugly. Practice on
some of the foam already cut off in the 48" circle making operation.
With an indelible felt pen, draw a straight line from the center of the patch
side to an edge. Label this line "Vertical"
Now, 90 degrees off from this "Vertical" line, draw another line and label this
line "Horizontal". These lines define the feed axes.
Cut two oblong 1/2" wide holes through the foam ; center on the vertical line
and then the horizontal line. Start the holes at 5" from the center
and end at 7" from the center.
Just on the reflector side of the oblong holes trim back the foil 1/4" to avoid
accidentally shorting the center conductor to the reflector foil.
Attaching fittings to the foam
Cut two 4" x 4" x 1/8" aluminum squares to reinforce to foam at the center or
the first wind will tear your 2M patch to shreads. Drill a 3/8" hole in the
center of each square and mount on either side of the foam
center with the bulk of the bolt on the reflector side
Cut four more 4" x 4" x 1/8" aluminum squares for the coaxial connectors
Drill a ~ 1/2" hole in the center of two of these plates and mount the conectors
with 4-40 bolts and nuts.. Solder the center terminal extending
bolts to each connector. Drill a 3/16" hole in the center of the last
two plates .
Draw four indelible 6" long lines perpendicular to and across each oblong hole
on both the patch side and the reflector side. One set of lines is 6"
out from the center hole and the other set is 6 1/2" out from the center hole.
The line set 6" out is labeled "50 ohm feed point, and the 6 1/2" out line set
is labeled 100 ohm feed point, which is used if running circular polarization.
I recommend starting with the linear V or H feedpoints. Mount the two SO-239
plates from the reflector side lining up each at the intersection
of the 50 ohm feedpoint and the Vertical or Horizontal line, and put the
bolt hole plates on the patch side over the bolts extending through from the
reflector side and tighten securely without too much pressure that will break
the solder joint on the connector's center pin.
If you wish to try circular polarization, then mount the connectors at the 100
ohm feed point (since they will be two feeds in parallel equalling 50 ohms.)
Using the dual feed 2M patch
I have used a lot of foam coming up with this design, and it should be
very close to a 1:1 match. The slotted holes permit perfection in the
case your foam has, say, a different velocity factor or your circles (or
mine) are not perfect. With a litlle jiggling of the feedpoint I have seen a
perfect 1:1, and then mounted it on the mount outside, only to see it go away
due to no ceiling reflection from inside my garage. I use both an AEA VHF-UHF
graphic SWR analyzer and the MFJ unit. Both tell me when it is perfect.
My first contact with a 2M patch was the International Space Statiion on 145.8
packet. I copied the signal very strongly from horizon to below
the horizon! I was visualy watching the ISS just after sunset, and I could still
pick up the signal very strong when the antenna was turned 90 degrees away from
the ISS.
Align the antenna with the horizon so that horizontal is horizontal, of course.
But if circular, orientation is meaningless. I use a signal source slowly revolving
at about 10 RPM to test polarization and circularity. My signal source
is in a diecast box and consists of an 8 MHz TTL oscillator heat sunk to the
diecast box directly feeding a 1/4 wave whip. Also inside is a 5 cell
NICAD batttery feeding a 5 volt regulator.
Circular polarization
Move both feedpoints to the 100 ohm feedpoint positions. Put a Tee connector
on each SO-239. Then connect a 1/4 wave of 100 ohm coax between the two
tees. RG-62 is close at 90 ohms but I could not find any in my junque
box. So I used 75 ohm RG-11 foam coax. Figuring in the velocity factor
it comes to about 17 1/2" long for a 1/4 wave at 145.99 MHz. I attached
a PL-259 to each end, formed the coax into a semicircle and attached each PL-259
to one of the tee ends.
Attach the coax leading to your rig to either the free horizontal tee end or
the free vertical tee end you wil get either right circular or left circular
polarization. With Suitsat, which uses a whip, either circularity should
work, but 3 db down. But no 3 S unit dropouts will be the big advatage if you
can withstand the 3 db constant penalty. When Suitsat was deployed, it was launched
with a lot of roll, about a turn every 6 seconds. If using a linear polarized
antenna, either horizontally or vertically polarized, to receive a 36 second
picture you can count on an image with 6.dropouts
Especially if you are new to SSTV, I would recommend that you do not try to copy satellite video real time. Instead, digitally record it with your computer in Stereo. Set one channel to the output of a transceiver or HT looking at the vertically polarized signal from the 2M patch and record the other channel from a second transceiver hooked to the horizontally polarized connector on the 2M patch. This is tricky so if in doubt, have a high school student help you! I am planning to use "Sound Forge" to record a *.wav file for each pass, making a CDROM of it and I hope to use some multichannel sound software to output a perfect file. Sort of like the old diversity reception with a twist. The signal will be at least 10 db down from that of the ISS. A preamp between the patch and Transceiver or HT might be a good idea.