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Author Topic:   Crafty Marine Antenna Design
jimh posted 01-01-2013 12:28 PM ET (US)   Profile for jimh   Send Email to jimh  
I recently came across the Shakespeare marine antenna model HS 2774-1. The design of this antenna is protected by a U.S. patent, No. 5,982,332, making the details of the antenna design available to interested readers. The patent information is easily retrieved from f=false

The patent describes in precise detail the method of the invention. Much of the description is quite technical, and will confound readers except those extremely familiar with antennas, transmission lines, matching techniques, and the other advanced elements of the art of antenna design.

Of more general interest to me (and perhaps other readers) is the configuration of the antenna having a quarter-wavelength choke section at the base of the radiating elements, which is intended to suppress flow of antenna currents onto the transmission line feeding the antenna. Many simpler, less well designed (and much less expensive) marine radio antennas omit such devices. The benefit of the choke section as mentioned in the patent is to produce very good antenna VSWR matching. However, I also believe the sophisticated choke design helps in the radiation pattern. Indeed, the data supplied in the patent shows that the antenna's radiation pattern is very clean and concentrates the main lobe of the pattern precisely at the horizon. (See figures 16 though 18 in the patent.)

The patent reveals the technical ingenuity which was employed in this design. I admire good design which provides benefits from the use of careful configuration, and this antenna certainly satisfies that criterion. Therefore, I admire this antenna, and the skill of its designer, John R. Lewis.

While the antenna is a bit expensive for recreational boat use, and its very wide band VSWR response not particularly necessary for use confined to the VHF Marine Band, its nice design and military grade construction might make it attractive for someone looking for "the best" antenna. The lowest price I could find was $235.

jimh posted 01-01-2013 02:03 PM ET (US)     Profile for jimh  Send Email to jimh     
One application for a wide-band antenna on a small boat might be use of a Amateur Radio and a Marine Band VHF radio sharing the same antenna. The Amateur Radio Service 2-meter band is 146 to 148-MHz, and a wide band antenna such as the Shakespeare HS 2774-1 would be useful for a transmitter in that band, as well as the VHF Marine Band at 156 to 162-MHz.
Jefecinco posted 01-01-2013 07:58 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Is there an expectation this 6 foot six inch antenna will perform better than an eight foot antenna? Will it have greater range or improved reception quality or signal quality?


David Pendleton posted 01-01-2013 11:59 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Since there is no 8' version of an antenna for the frequencies this antenna covers, I'd say no. There is no such expectation.
jimh posted 01-02-2013 09:11 AM ET (US)     Profile for jimh  Send Email to jimh     
I would never prejudge performance comparisons on the basis of the length of the antenna. The antenna under discussion is a very well designed and apparently well made antenna. I would expect it to work better than many poorly designed and poorly made antennas that might be longer in length.

In a marine VHF communication path, the general expectation is the antenna should provide maximum signal at 0-degrees elevation or right toward the horizon. There is no guarantee that every antenna will be able to accomplish this.

Jefecinco posted 01-02-2013 01:56 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     

Oops. I don't know why I assumed the antenna was designed to be used with marine band VHF radios.

Thanks for the gentle correction.


David Pendleton posted 01-02-2013 03:23 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
This antenna absolutely could be used for Marine VHF communications. The antenna is resonant from 136-174 MHz. As Jim indicated earlier, the Marine VHF Band is 156 to 162-MHz.

I wouldn't purchase an antenna like this unless I had a use for the other frequencies it covers, like the Ham 2-meter band.

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