Tuesday, September 14, 2010
How to build a $5,000 dollar UHF SATCOM antenna for under $20 Part 4-1
DIY: Military UHF SATCOM antenna
By Steve Douglass
Authors note: The construction part (since it is complicated ) of this ongoing series of articles will be spread out over several postings.
Be patient! Following parts will be posted shortly.
First a disclaimer:
You may or may not be able to build your DIY SATCOM antenna for under twenty bucks.
Yeah- I know that’s the title of this series of articles - but how expensive your antenna will be is conditional on the tools you have on hand and the antenna materials you may or may not have access to. Still, if this rig costs you fifty bucks, you’re already way ahead of the $5K cost for a new SATCOM antenna.
Some of the parts I already had were aluminum antenna elements (rods) salvaged from on old two-meter Ham antenna, coax and various RF connectors, not to mention a sturdy tripod (used and bought originally for $10 on Ebay) also some hollow antenna tubes from a broken Radio Shack Discone antenna.
One could easily use aluminum metal (welding) rods also available at Home Depot. Buy them along with the various sizes of PVC pipe used for the main antenna structure and most everything else.
Nylon cable ties (various sizes)
Two aluminum yardsticks (Home Depot $3.00 each)
Two (TV type) panel-mount F- connectors. (Radio Shack #278-212) $2.19 (2)
12 feet of RG-6 coax, plus four more F-connectors (Note: The Home Depot (crimp) ones are better than the Radio Shack.
1 Radio Shack F connector coupler (#278-304)
8 short (half-inch long) wingnuts & corresponding bolts (doesn’t matter what size) these will be used to hold the main antenna elements together.
Assorted screws and nuts and five feet of solid copper (insulated) wire.
Black electrical tape
Black spray paint (optional)
I used black spray truck bed-liner paint to give it a cool heavy-duty military-textured look.
Six feet of ½ inch PVC pipe (Note: all PVC is Schedule 40 for rigidity and weather ability)
Six ½ pipe PVC connectors
1 ½ inch PVC end cap
Six feet of 3 inch PVC pipe
Two 3-inch PVC end caps
One 3-inch PVC T- connector
One 3 inch to ½ inch PVC (fitting/coupler)
6 feet 3/16th heat-shrink tubing (available at Harbor Freight or Radio Shack)
Tools: Soldering Iron
Handsaw for cutting PVC pipe.
Propane torch to shrink, shrink-tubing (or you can use a lighter or even a hair drier)
F-connector crimping tool
We will start with the “element director boom” since it’s the easiest part to build.
This boom will hold eight x-crossed (parallel) metal elements – each 15 inches long and spaced five inches apart with the last element spaced 4 inches from the flat receiving elements.
CLICK TO ENLARGE:
First cut a length of ½ inch PVC pipe to 32 inches. Decide which end will point toward the satellites and measure & cut (from the end every 4 1/4 inches) until you have seven pieces of pipe.
Next re-connect the sections with six 1/2inch pipe connectors. Don’t glue these if you want your antenna to be portable. On the sky-end you’ll mount a ½ inch PVC cap and on the far end you’ll mount a 1/2inch to 1 inch PVC adaptor pipe.
From the end (with PVC connectors installed) measure in five inches increments and mark the spot- most likely in the middle of the connector. Element spacing isn’t very critical at this point so don’t sweat the details.
At each increment you will drill a hole through the connector and ¼ inch behind it for the corresponding cross element. The size hole you drill will be dependent on what you are using for metal antenna elements. Just make sure they fit snugly. I learned it is better to be to small then too big. You can always make the drill hole bigger, if you need to. See the photo if you are confused.
END CAP and ELEMENTS (painted) showing X element CLICK TO ENLARGE
NOTE: A drill press will insure your holes are perpendicular to each other in a perfect cross shape.
FINISHED BOOM SHOWING ELEMENT ALIGNMENT:
Each metal element (rod) should be cut to 15 inches and inserted into each hole with ¼ inch space between the two crossed elements.
Once all the rods are inserted – and made parallel you can drill and add small self-tapping set-screws to hold them in place – or glue them with PVC cement if you don’t plan on making your antenna come apart for portability. Each (crossed) element can be secured to each other (Inside the PVC pipe) with a nylon cable tie. Cut off the long (loose) end of the cable tie.
SEE ALL RELATED POSTS HERE
Posted by Steve Douglass at 7:40 AM