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Wi-Fi on board, part II

Jul 17, 2012

In my last article we talked about the frequency and data rate of Wi-Fi. With that covered, now is an opportune time to bring up some important correlations between these two signal parameters. There is a relationship between a signal’s bandwidth and its data transmission rate. In fact, this rate is proportional to bandwidth.

What this means in simple terms is that the higher the frequency, the higher the data rate. Wi-Fi frequency is quite high and at 2.4 Ghz is in the ultra high frequency (UHF) band and that is why it supports up to 11-Mbps data rates, but what is good for high data rate is bad for long-range radio frequency transmission due to atmospheric attenuation and other factors. Thus, the further out to sea we find ourselves the more we will need to use medium and high frequencies (MF/HF). Although these are a lot lower frequency than UHF, under the right conditions they can make it to shore. MF/HF signals have an effective range from 30 nm up to thousands of miles. While MF/HF transmissions will reach, we will pay a high performance price for drastically reduced data rate of MF/HF signals.

If we limit our voyaging range to within 30 nm of shore we can still use our cell phones for surfing the Internet by incorporating a signal booster, repeater, or amplifier along with an outside antenna. You can read more about cell phone boosters in a previous e-newsletter by clicking here. When we go beyond this range then we can still send and receive e-mail by switching to HF SSB radio, but will not be able to surf the web due to insufficient data speeds (1 to 5 KB per minute).

There are several options for e-mail over HF radio, but I will only talk about two of them: commercial SailMail and amateur radio WinLink 2000. Of course, the common elements to both systems include the HF radio, antenna, HF modem and laptop computer.

SailMail is a non-profit association of yacht owners that operates and maintains a world-wide network of SSB-Pactor radio stations thus providing an e-mail communications system for use of its members. Their custom e-mail protocol implements compression, virus filtering, spam filtering, and attachment filtering to substantially reduce the number of link-turn-arounds and improve communications efficiency. It is reported that members are able to send and receive e-mail at a rate varying from 10 to 500 characters per second using Pactor-III modems. Membership assessment is $250 per vessel, per year and is subject to change in the future. This represents, however, a highly cost-effective high seas e-mail service that allows one to stay in touch with the folks back home for up to 90 minutes per week. Once you purchase your Pactor modem you need to hook it up to your HF radio and laptop, download the AirMail software, set it up, and learn how to operate the system. For more information go to www.sailmail.com.

If you are an amateur radio hobbyist with a general license then WinLink 2000 is a viable option for you to take advantage of global Internet message forwarding. WL2K is a worldwide system of volunteer resources supporting e-mail by radio, with non-commercial links to e-mail. Usage and software are free for all those who qualify. This is another all-volunteer, non-profit service that functions only through the unselfish efforts of hundreds of amateur radio operators around the world. WinLink 2000 provides radio users and Internet users with seamless, transparent e-mail with attachments of reasonable size without the need for additional training. This allows any mobile or portable operation to interface into the e-mail system from anywhere on the globe that a radio connection can be made. With the WINMOR protocol the use of a computer soundcard is used instead of a hardware modem, which is a rapidly growing option that many choose. For more information go to www.winlink.org.

Just when you thought your Internet surfing was a luxury of the past...stand by for part III in which we will talk about a third option: satellite communications. With satcom you can have your cake and eat it too...but it will cost you! See you next time for part III, but in the meantime wishing you all: Fair winds and following seas.

 
About the author:
Fredrick Gary Hareland holds an AAS degree in rescue and survival operations and in avionic systems technology and is a certified marine electronics technician and NARTE certified telecommunications technician. He has served in the U.S. Navy, Coast Guard, the Military Sealift Command-Pacific and has worked for Maersk Line Limited and Norwegian Cruise Line. Hareland currently works at China Lake Naval Air Warfare Station as a microwave-communications technician. He lives in Ridgecrest, Calif.
 

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