Northwest Fisheries Science Center

Installation

Installation

Attachment Methods

Antenna housings constructed from PVC pipe do float; consequently, they must be firmly secured to the stream channel.  Stream characteristics will be the primary factor in choosing the antenna design and attachment method. 

Antenna housings can be anchored to a stream channel in several ways.  One method is to tie the antenna to eye bolts attached to wedge anchors that are secured in large buried rocks.  Wedge anchors should be at least 12.7 mm in diameter. 

Photo of anchors used to secure antenna housing to the stream bed.Pivot anchors used to secure the antenna housing to a stream bed.

A second method is to attach the antenna housing to a structural member, such as a length of steel or fiberglass angle bar.  This structural member is then attached to the substrate with wedge anchors, rebar, or pivot anchors. 

A third method is to drive construction stakes or rebar into the substrate on either side of the antenna housing and secure the housing to the stakes with rope or webbing.  Regardless of the attachment method, it is important to attach a safety line to the antenna in case it breaks away during adverse stream conditions.

Cabling

Antenna cable is a critical component of the system.  Cable length does effect PIT–tag reading range and is specified by the manufacturer for some transceiver models.  For example, systems using the FS1001M transceiver perform best if all antenna cables are of similar lengths (either shorter or longer than 15.2 m). 

We typically use a 1.5–m pigtail cable fitted with a male connector at the antenna end and a detachable, wet–pluggable female connector at the transceiver end (specific brands and models are available from the authors).  This configuration has several advantages:

  • •  Connector pins will not short out if the transceiver is accidentally left operating while someone is handling the cable.
  • •  The a pigtail length of 1.5 m allows most connections to be made out of water.
  • •  Antennas can be installed or removed without handling a long length of cable. 
  • •  Antennas dislodged by debris or high flows will break free from the cable, reducing the chance of cable damage.

Antenna Configuration

Antenna configuration will strongly influence both data collection and security.  To maximize data collection, antennas should span the entire stream.  Thus, a transceiver that can operate multiple antennas offers flexibility and is often the best option for achieving optimal configuration. 

Individual antennas can be used together to span the entire stream in a single array or to span part of the stream in two separate arrays.  Because two arrays are need to determine which direction tagged fish are swimming, some researchers prefer this configuration, even if neither antenna spans the stream completely. 

To maximize data collection, they place antennas in the thalweg, where most fish swim.  Placement in the thalweg does increase susceptibility to damage from debris and high flows, but this is often necessary if sufficient information is to be obtained.

For streams with no distinct thalweg, separate antenna arrays may be installed near the shoreline. 

Antenna security and site safety also need to be considered:  many streams and surrounding areas will be used for fishing, hunting, and boating. 

As a precaution, signs may be placed upstream and downstream of each antenna array to warn of potential navigation hazards and explain the purpose of equipment.  Such signs may discourage vandalism or theft.