Coach Thrasher

Waterproof Cox Box Recording and Radio Comm

Palo Alto Rowing Club has purchased two NK "Cox-Box Radio/Audio Recording Adapters" for use by our crews. I wanted to improve the setup by allowing the use of both a radio, and a digital recorder, in a waterproof box.

The adapters that we've been using are found on the NK website here: NK Radio Adapter

I've started creating a prototype, but I need to know what the RC values are in the filter embedded in the NK recording adapter. I specifically like to know what kind of RC filter to build into my waterproof box per the details below. I assume it would have the same values as found in the NK Recording Adapter.

I may be wrong in that NK is not using an RC filter, but the website indicates that the device prevents DC current with a capacitor, and reduces the volume of the radio with a resistor - so in technical terms, it sounds like they're using a high-pass RC filter.

One of the problems I have with the NK Recording Adapter is that the recording/playback electronics are not water resistant, and I'm very concerned that they will get splashed by the salt water that we row in, thereby ruining the electronics. That's why I'm using the Pelican (waterproof) box, and why I can't use the NK Recording Adapter's circuit - as there is no BNC connector in the box.

I'm including a few pictures of what I've built so far for clarification. Note that I have tested the whole configuration using the digital recorder and the radio simultaneously, and it works great. The caveat with that setup is that the radio is exposed to water damage. I'm trying to prevent that by using the pelican box. Please let me know what you think about this idea!

Figure 1: This is how we started using the NK Recording Adapter. The problem with this setup is that our radio is not protected from splashing water. If we row in the rain, or have rough water, it will ruin the radio. (Note: that the cable in this image has been cut for my modifications, but it was not cut when used as designed.)

Figure 2: The digital recorder has been mounted inside a Pelican waterproof box. This allows me to record the coxswain's verbal commands through a practice, and to use the audio as training material for other coxswains later. A BNC panel-mount connector has been mounted in the lid, and an audio plug (3.5mm) has been soldered inside the box to allow connection to the "mic" side of the recorder. I used digital-tv coaxial cable and "F" connectors with BNC adapters to create a custom extension cord from the Cox Box to the Pelican box.

Figure 3: This is a view of the inside of the Pelican box, with the panel-mount BNC clearly visible.

Figure 4: Here's a view of the outside of the Pelican box. The coax cable's F connector, and BNC adapter are clearly visible here. The other end of the coax cable has the same connectors. (Note: I don't have a crimp tool for BNC, but I do have a crimp tool for F connectors. I like the BNC design, so that's why I'm using so many connectors.)

Figure 5: This view gives the desired configuration. Both the radio, and the digital recorder, will be wired inside the Pelican box to waterproof them. You can see that the radio has a 2.5mm jack and a cut wire attached - this is the cut end of the NK Recording Adapter. The BNC end of the NK Recording Adapter is not used because there is no BNC connection inside the Pelican box. The wires need to be soldered to the inside of the Pelican box's BNC connection, with the RC filter circuit, such that the radio does not feed too much power into the circuit. This illustrates why I need the RC values of the NK Recording Adapter's filter.

Figure 6: This is a view of the radio, and digital recorder inside the Pelican box. This will allow recording, and radio communication, with the crew at the same time.

Posted at 01:47PM Feb 01, 2006 by jason in Hardware  |  Comments[2]