Due to higher and higher construction costs and the dire need for PIT tag detection at critical points such as the adult ladders at The Dalles and John Day Dams, the PTAGIS Kennewick group embarked on an effort to build a pass-through thin body antenna. The goal of the thin body antenna is to be only two inches thick and still detect at the same high level of efficiency that is expected at all other PTAGIS main-stem detection sites.
In the past, at all other adult ladder detection points, it has been necessary to excavate large areas of concrete to house the standard thick bodied antennas and keep them from field-coupling to ferrous rebar. The new thin bodied antennas are possible due to the use of ferrite tiles embedded into the antenna housing.
As of September 25, 2012, these goals have been met. A prototype antenna was built at PTAGIS Kennewick and tested at the NMFS Pasco facility. The prototype was built with the goal of later building four of these antennas for the counting window slots at The Dalles North and East ladders. The PTAGIS staff is currently working with the USACE to install these antennas at The Dalles during the winter work period. Due to the tight schedule it is unknown whether this will take place.
If scheduling works out, this temporary system will be installed at a relatively low cost since no concrete cutting will be required. The system is projected to read at near 100% detection efficiency and be maintained at near 100% uptime. The antennas should last 10 years or more. Below are conceptual drawings for installing these antennas at The Dalles North. The Dalles East will be similar.
The PTAGIS crew is currently working on a smaller footprint antenna that will reduce the “speed bump” length by four inches and should reduce the cost and weight of the antennas.
It should also be noted that these antennas can also be embedded in the concrete by excavating a slot the same size as the antenna. They can also be mounted on a metal surface. A full technical report is available at: ftp://ftp.ptagis.org/Documents/Newsletters/Volume_10/Thin_Bodied_Eval_0_1r2.pdf.