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Remote Transducers for Anabats
( This page may take a minute or two to load ... there are a lot of images !! ) The concept behind the shrouded extensions is simple ... move the transducer away from the gear, so the gear can be protected and the transducer can be best positioned to get bat calls. To minimize environmental exposure to the transducer over long periods of time I've been employing a technique that involves using a PVC housing to shroud the transducer, pointing the transducer down, and then using a reflector to angle in bat calls. A bat monitoring station using this concept had been in service for over a year, and proved very workable. These instructions were updated in March, 2004, to show the use of a cable gland on the back of the connecting cell going into the shroud. The changes were made to better provide an essential weather tight fitting on the back of the shroud for the cable that could more reliably be replicated and serviced. Special Note:
Tracy Allen,
( www.owlogic.com
) has also been working on Anabat transducer
extensions and reflector mounts for the field. His field
tested configuration employs a formed aluminum bracket,
and a fully potted connector cell. Tracy accepts orders
to fabricate these extensions for others. For more info,
contact Tracy at: tracy@emesystems.com |
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The system at the left is a solar powered, bat activity monitoring station deployed by Bill Rainey. Note the use of the shrouded transducer extension and reflector. The monitoring array below is my original design prototype and concept model. |
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| To construct these remote
transducer assemblies, there are essentially two steps:
Make the actual extension cable; and then fabricate the
shroud housing, and reflector assembly. Below is an
overview of the process. |
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Construction
Cable: The cable I use is CANARE brand type 4E6S star quad 4 conductor audio cable. It is extremely flexible and durable, and has a high density shield. As it is the only cable I have thoroughly tested, it is the only type I can recommend. This type of cable is available from www.markertek.com. NOTE: If you are extending the STANDARD Anabat transducers, you should keep the length of your extension cable under 2 meters. If you need a longer extension, you should use an Anabat HI-MIC transducer. An Anabat LO-MIC can be safely used with extensions up to 5 meters in length. Connectors: For each extension cable, you will need two 8 pin Deltron metal DIN connectors, which are available from Mouser Electronics - www.mouser.com. The part numbers are P/N 17HR618 - male cable connector, and P/N 16HR658 female chassis connector. PVC Parts: You will need a quarter inch wide "ring" of .5" schedule 40 PVC to mount one of the DIN connectors with, and a .5" PVC slip coupling that is sized to nest into a .75" coupling. You also need a .5" end plug which is tapped for a .25" pipe fitting ( available from www.PlumbingStore.com as #438-072 PVC Bushing ). Cable Glands: Cable glands provide a weathertight means of conducting a cable into a sealed enclosure. Two cable glands are used for my extensions. One is for the cable exit on the connector cell. The other to facilitate weather proof connection to a NEMA enclosure for the Anabat gear. These items are selected for best integration
into the final shroud configuration and will be discussed
again during their assembly. |
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Building the Extension Cable Assembly |
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| Slide the shell from the male DIN connector onto one end of the cable, and prepare the end of the cable as shown. Note that the coax is heavily tinned with solder. This allows the connector to be soldered to the shield on assembly - important for good shielding from electrical interference !! |  |
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| It may also be easier to make up the connector by clipping away the contacts that are not used. Here you see the connections that are left for use on the insulated insert for the male connector. A pair of small wire cutters work well at this point. |  |
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| Next make the connections ... note the Blue - White - Blue - White soldering pattern. If you use follow the alternate color order of the cable when wiring, it is fairly easy to match up the other end with an ohm meter when that end is wired. |  |
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| The metal strain relief is now
crimped into place on the shield, and solder is flowed
around the joint. Be careful to use just enough heat to
flow solder through the joint - and not so much as to
melt the cable !! Check the connections visually and be sure there are no solder splashes or loose wires that can short. |
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| Finally, pull the metal shell up the cable and over the wired assembly. A single screw fixes the entire assembly together. Sometimes it is advantageous to reloosen the screw a bit, and then insert the connector into a socket and retighten the screw. This works out any alignment problems that can creep into the assembly. This end of the cable is finished. |  |
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| This is also a good time to consider how the cable will be routed to the Anabat detector. If it will need to pass through the wall of a weatherproof box or other container, you may want to slide a watertight cable grip over the cable at this point. Note that the end with the white nut is inserted into the housing. |  |
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| When ordering a cable grip, you need to consider the size of the hole into the box, in relation to the cable connector size. You also need to be concerned about the thickness of the enclosure wall that the cable grip is mounted through. The grip pictured here will work in any enclosure with a wall thickness up to about 1/8". The part number I use is 288-1167-ND, from Digi-Key Corporation. | |||||
| The left image shows the exterior
view, where the cable enters the enclosure. The cap nut
tightens to compress a rubber gasket around the wire,
sealing the connection. Hand tightening is usually
sufficient. The right image shows the interior, where the cable has entered the box. The size of the hole drilled in the enclosure wall for this cable grip was 3/4". |
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| We now turn our attention to the
other end of the extension cable. The female chassis DIN
connector will be mounted into a .25" ring of
schedule 40 half-inch PVC pipe, and the connector will be
wired and assembled into a cell composed of a half-inch
PVC nested slip coupler, plugged with a tapped PVC plug.
The nested coupler has an inside diameter that
accomodates half-inch PVC pipe, and an outside diameter
that matches three-quarter-inch PVC pipe. A PG7 sized cable gland, part number 288-1164-ND, from Digi-Key Corporation , is used to provide a weathertight passage of the extension cable into the connector cell. ( If you have a source for NPT-1/4" cable glands, these will also work. The PG7 and NPT-1/4" are somewhat interchangeable.) |
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| Pre-assemble the back connector cell by cementing the threaded plug into the nesting connector. Then thread a PG7 cable gland into the plug, useing a little silicone glue/caulk on the threads. This assembly needs to be sealed solid !!! |
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| Slip the preassembled cell onto the end of the cable, cable gland first ... as shown. Strip a small amount of insulation from each wire and tin with solder. The shield is not connected at this end, so should be cut back so that none of the braiding is exposed. |  |
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| Here are two of the 8 pin DIN chassis connectors. The one to the left is as you receive it. The one to the right has been mounted in the PVC pipe ring, and has the extra lugs clipped off. I use a few drops of super glue around the back of the ring and nut to help minimize the chance of it ever loosening. |  |
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| Now comes the "trade secret" to wiring the extension cable correctly. Mate the DIN connector you are working on to the DIN connector on the cable end you previously finished. Then clamp the connectors in a vise as shown. Use a meter to find which wire matches the first connector tab and solder it in place. This assures that the wire is being connected to exactly the correct connection at the other end. Clever ... yes ??? |  |
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| The next wire in the rotation should be the connected to the next connector tab ( Again, check with a meter ). Note that it will be the opposite color of the first. Once that wire is soldered in place, the last two connections should be obvious -- following the white-blue-white-blue pattern. But it doesn't hurt to check each one before connecting. That way you are assured that the final cable is a true extension, and that you didn't cut any of the wrong pins :-/ |  |
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| In this picture, the final
connection is completed. Use your meter to assure
yourself that none of the wires are shorted to any of the
other wires. Also be sure to check that none of the wires
are shorted to the shield ( as measured at the metal
shell of the first connector you did ). Note that the shield is not connected at this end. That is not a mistake. Be sure that there aren't any shield wires exposed that might touch any of the pins in the connector. |
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| It is very important to protect the DIN connector pins from moisture. Coat the back of the connector and pins with silicone compound ( I use GE Silicone II ). After the silicone cures, which takes about 24 hours, the cell can be sealed up. Once the connector cell is completed, you should never have to go back in again. If the end of the cable fails in service, it should be cut off and remanufactured from scratch. |  |
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| When the DIN chassis connector is
wired and encapsulated, the assembly is press fit and
glued flush into the coupling to make a closed cell. Use
PVC type 705 glue for setting the DIN assembly, and
glueing the back plug into place. After the glue has dried, plug a transducer onto the cell connector, and plug the other end of the cable into the transducer plug on the end of an Anabat. If everything has gone according to plan, you will have a working extended transducer. |
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Assembling the Transducer Shroud |
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| This is where it becomes apparent why the nested coupler is needed. The connector cell that the transducer mounts to must fit into the back of the PVC transducer shroud, which is formed from a .75" to 1.5" adapter. If the slip coupler used to make the connector cell wasn't a nesting coupler, it would not fit into the adapter !! But there is still an obstacle to be overcome. |
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| We need for the connector cell to fit all the way through the back of the adapter. But there is a stop ridge molded into the adapter specifically to prevent such a thing from happening. This is where a bit of crafting is required. Using a file, dremel tool, or whatever destructive force you have mastery of, grind out the ridge so that the connector cell will be able to be forced past the inside edge of the adapter. |  |
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| Here is a ground out adapter that
has been fitted into the PVC fitting that forms the body
of the shroud ... a 1.5" x 1.5" x .5" Tee
fitting. You can see that the ridge has been fully
obliterated by malicious use of a dremel tool with a
router bit fitted. Be sure to take all safety precautions when doing this bit of work, as bits of PVC flying into your eyes can be very annoying in the least. |
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| Now the cell can be inserted into
the shroud assembly. First, press fit the cell into the
back of the shroud. Then, dab a bit of 705 PVC glue
around the crevice in the back of the shroud to seal
things up. If there is any failure of the seam around the cable, water can collect and be drawn inside of the connector cell and shroud with temperature fluctuations. It's not a bad idea to seal all of the joints around the cable, and the cable gland, with silicone compound... and fill any depressions so that water cannot collect on the back of the shroud. |
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| Here we take a little peek into the business end of the shroud. To the left, the transducer has been fitted into place to show the relative position that it will inhabit when the system is deployed. In the right image, note how the connector has been aligned to place the notch in the DIN plug in line with the bottom of the TEE fitting. This makes life easier when you go to assemble the unit later, as you will be able to keep track of how the transducer needs to be aligned when it is inserted into the shroud. |  |
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| If you are deploying the transducer as part of a long term system, I would also suggest using a good exterior caulk to fill the gap between the inside of the PVC shroud and the outside edge of the Anabat transducer. | |||||
Constructing the Reflector and Bracket |
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The reflector bracket for the
shroud is comprised of the following schedule 40, 1/2"
PVC components:
NOTE: These dimensions are for Lasco and Dura brand PVC components. You may need to adjust the lengths of A and C for other brands. |
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| Here is a fully assembled bracket, with the official Nevada Bat camo style paint job. I prefer to paint all PVC parts for two purposes ... to protect the PVC from the affects of our intense Nevada UV light, and to make the assembly a little less obvious out in the environment. If you decide to paint your transducer assemblies, be sure to mask off the areas that need to fit into other parts. Also, paint the shroud parts before inserting the connector cell - makes it easier to keep paint out of the connector !!!! |  |
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| The reflector is comprised of two
parts, a 4.25" x 4.25" of 1/4" thick
polycarbonate plastic, and a 1/2" PVC plug. I
originally used ceramic tiles, but the clear
polycarbonate squares allow you to see up into the shroud
to examine the transducer while deployed. The polycarbonate can usually be bought in small quantities at commercial plastic shops. I prefer to have a number of squares cut up for me by the shop. |
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| I use an alignment board to
assemble the reflectors. This is basically a piece of
cardboard that has the outline of the polycarbonate
squares marked off, with a pair of crossed center lines. Simply remove the protective covering from the square, daub a bit of PVC cement on the plug, and press firmly into place in the middle of the square, using the alignment board as a guide. Keep the piece flat for at least 10 to 20 minutes while the glue sets. |
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Putting It All Together |
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| All of the steps above give a
basic overview of how each of the elements of the remote
Anabat transducer assembly are made. These elements are
assembled to achieve the type of transducer
configurations shown at the top of the page. This basic
construction technique can be applied to other ends as
well. I have used the PVC extension idea to fabricate
remote cables for use with remote hand-held transducers,
tripod based portable passive systems, parabolic
reflector mounts, and even a 12 foot extension pole that
allows me to extend a transducer out over the opening of
a vertical shaft from a safe distance. I'll close this page with some illustrations ... and some acknowledgements... This type of work doesn't move forward without support and feedback from researchers who actually apply the technologies in the field and attempt to glean results from its use. I wish to acknowledge and thank my collaborators, who have helped fine-tune the remote transducer technique over the last year or so ( and are still doing so ). My heartfelt thanks to: Mike O'Farrell, Bill Rainey, and Chris Corben. |
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Tony Messina, Las Vegas, NV - page last updated 09/30/2004
