The transmitter attaches to the bird as a backpack using various harness materials such as Teflon ribbon, bungee cord, PVC tubing or other elastic material. The harness is looped under the wings and then around the base of the neck or around the abdomen (commonly known as a "belly cinch"). Backpacks are used on a wide range of species from songbirds to bald eagles.

Historically backpack transmitters were some of the first designs used to attach transmitters to research animals. One attribute of the backpack design is that the transmitter weight is carried in the center line of the bird's body mass. By doing so, a maximum allowable weight of up to 3% of the species weight can be used prolonging the life of the transmitter. The backpack also allows for a longer and stouter antenna than other designs further increasing field range and reducing antenna breakage.

Anterior and posterior holes for harness material are predrilled. Harness material is supplied by user.

Transmitter Series	Weight (grams)	Life (days)	Description
A1005	0.55-1.30	20-122	Smallest sizes, reduced power output for longer life, minimum potting for lowest weight., silver oxide battery. Limited frequency availability.
A1000	0.9-3.9	7-190	Small size, standard power output for normal life, normal potting for durability, silver oxide battery.
A1100	2.5-155.0	10-1095	Medium size, cylindrical shape, lithium battery.
A1200	4.9-15.0	13-510	Small size, coin shape, lithium battery.
A1300	11.0-25.0	60-550	Medium size, flat shape, lithium battery.
A1400	20.0-47.0	36-1100	Larger size, rectangular shape, vertically stacked lithium batteries (2).
A1500	40.0-62.0	130-1095	Larger size, rectangular shape, side-by-side lithium batteries (2).

The Dwyer backpack has been used exclusively on ducks. From its inception in the late 1960's to the late 1980's, it was the most frequently used transmitter attachment method for ducks. The transmitter package rides on the center of the duck's back with PVC and wire looping around the duck's body. The loop sizes are adjusted to fit the duck's body and fixed in place using PVC solvent cement.

In the past ten years, the Dwyer backpack has fallen out of favor. Reasons for using attachments other than the Dwyer backpack are reportedly higher success rates in nesting studies and reduced behavioral changes. Studies lasting 100 days or less often use other attachment methods (glue-on, prong and suture, subcutaneous, etc).

The Dwyer design is still the most widely used duck harness when long term studies are conducted. This harness can be used successfully for a year or more while other external designs begin to fall off at 70 days and few have lasted more than 6 months. By using a duty cycle option, duck transmitters can be made to last two and sometimes as long as three breeding seasons. The Dwyer backpack has the highest likelihood of success when an external harness is needed.

Includes harness material.

Transmitter Series	Weight (grams)	Life (days)	Description
A1700	15.0-36.0	24-590	Medium size, reduced footprint, higher profile
A1800	20.0-34.0	60-550	Medium size, lower profile, flat shape.