Coaxial Cable
Radio-Ware, http://www.radio-ware.com/products/rg174.htm RG-174 50 Ohm, micro-coax
Bought at Walmart is this Astak wireless video system. It even includes audio! And the price is great, just under eighty bucks. You simply can't go wring here. Below I chronicle how to convert the camera-transmitter in such a way as to make it suitable for operation in a submerged model submarine. Make sure that you pick up model number WL811TR.
Walmart tends to move on to different product types and manufactures, or to even drop a product type, quickly, so if you want one of these Astak units (I would recommend getting more than one), make that purchase now!
The only real challenge involved in readying the wireless video camera-transmitter for operation aboard the r/c submarine is moving its very short transmitter antenna off the back of the camera-transmitter case and sticking it within the plastic periscope head. This to get the antenna in line-of-site with the shore-side receiver. You only get an image and sound if the periscope head is above the water; this low power 2.4 GHz system must transmit and receive in air, not water.
To determine the amount of coaxial cable needed for the job I ran some down the periscope tube, into the sail and pushed the end into he mounted WTC's packing gland till it almost touched the forward lens of the WTC. Then, one inch over the top of the periscope tube (equating to the length of the original camera-transmitter's antenna) I cut the Coaxial cable free from the roll. Later, with its shield cut away, this one inch of cable conductor would serve as the systems transmitting antenna.
Guided by my discussions with Lee Smith, I worked out a drawing to direct me as I made the modification to the camera-transmitter body: basically, chopping off the case mounted antenna and substituting a length of small gauge coaxial cable (a shield inner conductor with a waterproof outer insulation jacket). Lee was an indispensable element of this project, he directed me on how to hook up the coaxial cable weave shield in such a way as to ground it so that only the exposed tip of the cables conductor would act as the above water transmitter antenna.
Here you see some of the tools used to prepare the wires and make the soldered connections needed.
The other major modification needed was to remove the big, bulky power jack, expose the wires and to solder each to a washer, the washers making up to a terminal lug on the inboard side of the WTC access cap. Note that the black (circuit negative) wire has a parallel leg that connects to the coaxial cable shield, effectively grounding it. Note that this shield ground wire is oriented a bit differently than what I illustrated in the drawing, just makes life a bit easier not having to bare wire and make a solder connection so close to the camera-transmitters case. Live and learn.
To act as a strain-relief I glued the coaxial cable to the back of the camera-transmitter case. This was accomplished by first removing the little self-adhesive sticker, roughing up the case with some #100 sandpaper, rubbing in some baking soda (to produce a high pH substrate that would readily accelerate the Cyanoacrylate glue to quick cure), laid down the coaxial cable, dabbed on the CA, and it was there for keeps.
This project involved some 'small stuff' soldering -- I was aided in those tasks by the use of this alligator-clip holding tool. Here I'm soldering the camera-transmitter power wires to their respective washers. Make sure that you use 'acid free' rosin/flux when working electrical circuits.
. The four wires between the camera-transmitter case and the access lid of the WTC are just stiff enough to insure that when the camera-transmitter is pushed into the cylinder that its lens will be pushed up against and in alignment with the WTC's lens.
To the outboard side (the wet side) of the access lid the projecting terminal lugs make up to the two wires of the lead the makes up to the nine-Volt battery within the models WTC -- this is how I turn the camera system on and off, just making or breaking the leads connectors (Futaba 'J' type connectors liberated from an old battery-switch harness).
A two-piece brass harness secures to the WTC. A singe stud, protruding from the top bracket of the harness passes through a hole in the bridge well where a capture nut hold it, and the attached WTC in place within the KAIRYU's sail. Things were arranged in there so that the porthole in the sails leading edge would sit right on the WTC's longitudinal centerline; right in line with the camera's lens.
I leak checked the completed WTC by removing the equalization valve's core-valve, slipping a flexible tube over the valve body and, while holding the unit underwater, blowing into the tube, over pressurizing the WTC, and producing bubbles from any leak points. In this case, no leaks occurred. Of course, as I did this I clamped the WTC between by fingers so the access lid would not blow off.
Note that I've put heat-shrink tubing over the antenna end of the coaxial cable. Had I not done this water would work its way between the shield and outer insulation wrapping and enter the WTC, flooding it out.
Once the camera WTC is secured within the sail the coaxial cable is run up through the vertical tube that forms the periscope foundation and up through the top of the sail. I then run the periscope tube over it, followed by the plastic periscope head -- the periscope head is bored out to receive the one-inch long antenna atop the coaxial cable. And that's all there is to it.
I put in two pieces of plastic sheet within the sail to form strain-relief brackets for the power leads that run into the hull.
Rose at the kiddi-pool checking the image from the sail mounted camera on the portable monitor sitting on the chair. For this test I made a portable battery-harness, what she's holding in her left hand. This permits us to test the installed system without needed to mount it to the hull proper.
Rose holding the sail underwater as she watches the monitor, using it as a 'viewfinder' to aim the sail to interesting objects she sees underwater.
Don't worry about the battery and leads sitting in the water -- fresh water has little effect, and it takes some time for what little galvanic action there is arc across the poles to significantly erode away the positive terminal. However, you would never get away with this in salt water. I simply don't understand how Mike Dory and the other 'Fresco' model boater's get away with that! Gobs of RTV sealant, I guess. Yuck!
And here's the proper hookup between upper and lower hull: the power lead from the main WTC's foreword bulkhead to the sail mounted video camera WTC.
The Astak unit is claimed to give a solid three-hundred-and-twenty-somenting foot range and I affirmed that one night. But the distance between camera-transmitter antenna and receiver antenna has to be unobstructed. These little transmitters only poop out ten (I hear even less) milli Watt's of power -- I assume this limitation is to keep them within the 'no code' user category, enforced by the Federal Communications Commission.