Comparisons of the STANDARD HORIZON HX851 With the NAUTILUS Lifeline DIVER

I was one of the early pre-orders of the NAUTILUS LIFELINE DIVER VHF Radio (with GPS and DSC capability). By profession, I’m an electrical engineer and have worked on several industry-leading radio designs in my last 12 years with Qualcomm Inc. So the first thing I wanted to know about the NAUTILUS LIFELINE radio was its design specifications and performance benchmarks.

When I first unpacked my LIFELINE and looked at it and held it in my hands, a couple of things quickly stuck out to me.

The first thing I noticed was that the weight of the LIFELINE was concentrated within a small form factor. It felt to me like it was too dense of an object to be positively buoyant. Since the only time, the LIFELINE could be used is when the diver is floating on the surface, the diver’s preference should be for the radio to be Positively Buoyant, so that if the radio became untethered or slipped away from the diver, it would float and the diver could hopefully retrieve it.

But when you open the top cap of the LIFELINE to operate the radio, it is negatively buoyant and will immediately sink if the diver loses its grip on it. On the surface I want all of my Emergency equipment to Float.

The second thing I noticed was that, unlike most handheld VHF radios, there was no external Antenna SMA connector because the LIFELINE’s antenna was integrated with the transceiver circuitry inside its housing. This meant that the LIFELINE’s antenna could not be disconnected, and extended away from the handset itself. Why is this important?

VHF signals are line-of-sight signals, meaning that the VHF signals can be blocked and distorted by any obstructions between your radio and any other VHF radio. So it is important to locate the radio’s Antenna as high above the water surface as possible, to get above waves that will block your signal, and to help avoid signal distortion from multipath signal reflections coming off of the water surface that can interfere with your primary signal.

The obvious way to do this is to add a low-signal-loss extension cable between the radio handset and the Antenna and to use your SMB as an Antenna Mast and thereby gain some height above waves and also extend your radio’s transmit and receive range. But without an external SMA Antenna connection, there is no way to elevate the NAUTILUS LIFELINE’s antenna independently of the radio handset itself.

The NAUTILUS folks are aware that their product’s design inherently limits the radio’s signal range (see specifications below) because, in their Usage Documentation for transmitting the Distress Alert Messages, they state “For maximum range hold Lifeline as high above the waterline as possible”.

What they do not tell you though is that when the Coast Guard receives your emergency DSC Distress Alert Messages, your MMSI identifies your radio, and the Coast Guard immediately sends a command back to your radio that will cause it to retune to VHF Channel 16 so that they can “talk” with you. VHF Channel 16 is also continuously monitored by all VHF radios, so everyone within your signal range (i.e. potential rescuers) is a listener to the emergency conversation.

So you are going to have to lower the LIFELINE from your outstretched arm’s length to your mouth, to talk into the radio’s microphone, and doing so will limit your signal range and possibly make your emergency voice communications with the Coast Guard impossible. Being able to communicate by voice over the widest area possible, is crucial to your successful rescue.

The following is a comparison of the NAUTILUS LIFELINE DIVER with another handheld VHF radio, the STANDARD HORIZON HX851, also with GPS and DSC capabilities.

My side-by-side comparison of the two manufacturers’ design specifications, performance benchmarks, and some field test results is shown in the table below. I’m not claiming that this is a rigorous comparison but it is more than sufficient to distinguish between the performance of the two radios.

Maximum Transmit Power Out
LIFELINE: 1.85 Watts

Receive Sensitivity
LIFELINE: Not stated in their user documentation.
STANDARD HORIZON HX851: 0.25uV for 12 dB SINAD (Benchmark for best handheld VHF radios)
(Note: Many hours of side-by-side field testing, have shown that the STANDARD HORIZON HX851 can clearly receive VHF transmissions which my NAUTILUS LIFELINE cannot.)

Height of Antenna above Water
LIFELINE: Your arm’s length
STANDARD HORIZON HX851: 5 ft. using a low loss antenna extension cable and an SMB as your antenna mast

Range of Signal for Voice
LIFELINE 4 – 5 miles. (Field testing results in the following independent review, have lowered this range to 2.5 – 3 miles. See Scuba Gear Reports Field)

Range of Signal for DSC messages
LIFELINE: 8 miles

Speaker Audio Power
LIFELINE 400 mW into 8 ohms @ 10% THD
STANDARD HORIZON HX851: 700 mW into 16 ohms @ 10% THD

Does it Float?

Some conclusions on the performance capabilities of these two marine VHF radios:

• Per the manufacturers’ stated Max Transmit Power specifications, the STANDARD HORIZON HX851 far surpasses the NAUTILUS LIFELINE DIVER.

• NAUTILUS Lifeline does not state their Receive Sensitivity specification in their user documentation, but many hours of side-by-side field testing have shown that the STANDARD HORIZON HX851 can clearly receive VHF transmissions which the NAUTILUS LIFELINE DIVER cannot.

• Per the manufacturers’ stated specifications, the STANDARD HORIZON HX851 has a significant additional Voice range over the LIFELINE.

• Per the manufacturers’ stated specifications, the STANDARD HORIZON HX851 has a significant additional DSC message transmission range over the LIFELINE.

• The Antenna of the STANDARD HORIZON HX851 can be elevated 5 ft. above the water. The LIFELINE’s Antenna cannot be elevated higher than arm’s length and the radio cannot be used for Voice communications when held in the floating diver’s outstretched arm.

• The audio speaker in the STANDARD HORIZON HX851 has a much louder audio output than the LIFELINEs, which is very helpful in windy conditions.


The STANDARD HORIZON Marine Division has over 50 years of experience as a leader in VHF Radio design, GPS Receiver design, and marine communication electronics production. They are widely recognized as an established industry leader who consistently produces best-in-class products.

There are several other features and functions of the STANDARD HORIZON HX851 that distinguish it further, as being the best VHF handheld radio for a diver in an emergency. But I will leave it to the diver to compare these two radios further.



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