VR4-UWM : Underwater Modem Receiver

How long will my VR4-UWM battery last?

VEMCO offers two battery options for the VR4-UWM, lithium or alkaline. While lithium batteries have a much longer life (see table below), their transportation is governed by dangerous good regulations. Alkaline battery packs do not have any transportation restrictions but have a much shorter life.

The battery management display in VUE give an accurate indication of the remaining capacity of your receiver’s battery, making it easy to plan and schedule replacements. For information on replacing your receiver’s battery, please refer to Section 5 of the VR4-UWM User Manual (see Downloads section). Receivers may also be sent to VEMCO for battery replacements which would also include the pressure testing of your receiver to ensure proper sealing. Please contact our support team for the required shipping information.

I am having trouble establishing a connection with my receiver using the acoustic modem. What should I do?

Acoustic communication can be challenging due to different environmental conditions which may affect the acoustic properties of your deployment area. It is very important to be patient as it does take time for the VR4-UWM to receive the command and make any changes.

• Try to limit adding any additional acoustic noise to the area (boat engines, depth sounders, etc.)
•  If available, use a VR100 to confirm communication between the VR4-UWM and the Benthos Transducer – channel set to 20 kHz with a low manual gain setting (<12 dB).
• Power Scale: 0 dB is the highest power (signal strength) and -21 dB is the lowest power level. If you are drifting towards or further away from the receiver, you may need to adjust the power up/power down settings accordingly. It is best to make these adjustments in small increments in an effort to limit any echo effects. It is also important that you adjust your power settings for your deployment environment. For example, if you are working in a reflective (e.g. hard bottom) or shallow environment, avoid using high power settings as this can saturate the area with acoustic energy and increase communication errors.
• Use the “status” and “range” messages to establish “good” or “very good” communication status, as these shorter messages are more likely to get through in acoustically challenging conditions.

For more information on acoustic modem communication, please refer to Section 3.4 of the VR4-UWM User Manual (see Downloads section) or contact our support team.

What is the maximum distance from a receiver that I can still communicate via the acoustic modem?

Depending on local conditions (geomorphology, wave action, depth, etc.), the maximum distance for acoustic communication will most likely be different for every receiver deployed. It can range from a hundreds of meters to over a kilometer. We always recommend that for every receiver, you keep a record of the power and bit rate settings as well as any relevant physical characteristics which may impact your communication success for future visits to the receiver.

Can I use this type of receiver in a VPS study?

Yes, the VR4-UWM receiver has the capability or recording detections with millisecond resolution, which is required for VPS positioning. For more information on our VPS systems, please contact our sales team.

Can I detect 69 kHz and 180 kHz tags simultaneously?

Yes, the VR4-UWM is a dual channel acoustic monitoring receiver that can operate at 69 kHz, 180 kHz or both at the same time.

Communication cut out in the middle of my download. Do I have to start the download from the beginning?

No, if communication to your VR4-UWM is interrupted during the download process, the receiver will continue to download from the last fully downloaded page of data when your connection is re-established. In your offloaded file directory, you will see 2 or more .vrl files for the receiver in question, depending on how many sessions are required to fully offload all data.

What is my modem address?

Every VR4-UWM is assigned a modem address between the numbers 1-249 so that it can be distinguished between different VR4-UWM receivers deployed within acoustic range of each other. Due to the limited number of available unique modem addresses, it is very important that researchers plan their deployment placement accordingly. Units with the same modem address should be deployed at least 5 km apart.

We recommend that researchers keep an up to date record of their receiver serial number, associated modem address and deployment coordinates.

Can I moor my VR4-UWM facing downwards for better coverage?

No, the VR4-UWM must be deployed in a vertical position with the acoustic modem pointing towards the surface to allow for acoustic communication with the surface modem unit.

Can I cover my receiver in anti-fouling paint?

While it is not VEMCO’s recommendation to cover your receivers, we do understand that certain environments do pose significant issues in terms of bio-fouling. If you decide to cover your receiver(s), it is extremely important that you DO NOT cover the three pressure relief valves or hydrophones. The pressure relief valves are located on the main body of the receiver as well as near the base of the hydrophone towers.

Can I deploy my VR4-UWM in Suspend Mode?

No, if the unit is deployed while in Suspend Mode it will not detect tags and you will be unable to communicate via the acoustic modem. The unit would need to be brought to the surface and taken out of Suspend Mode using Bluetooth communication.