Have tried a number of the "rabbit ear" type tv antennas for viewing at the dock with less than favorable results...was just wondering how the Seawatch brand of antennas by Shakespeare perform and if they are worth the money...any feedback greatly appreciated.
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Coast Guard advisory
Don't know abou the effectiveness of these antennas. But the Coast Guard Local 7th Distric Local Notice to Mariners (LNM) has been warning that these models (among other brands) have been found to interfere with other vessels' GPS, as far away as 2000 feet. I have seen this safety warning repeated in multiple LNM editions. The one I've just looked up is the Sept. 2003 monthly edition, which you can find at http://www.navcen.uscg.gov/lnm/d7/lnm0735.pdf
Don't know abou the effectiveness of these antennas. But the Coast Guard Local 7th Distric Local Notice to Mariners (LNM) has been warning that these models (among other brands) have been found to interfere with other vessels' GPS, as far away as 2000 feet. I have seen this safety warning repeated in multiple LNM editions. The one I've just looked up is the Sept. 2003 monthly edition, which you can find at http://www.navcen.uscg.gov/lnm/d7/lnm0735.pdf
Work well for TV reception
Interesting reading the Coast Guard report. I guess that I would think twice about watching TV while sailing in unknown waters. I have used a Shakespeare TV antenna for a couple years (dockside) and have had great results. I didn't want to mount it permanently on my mast, so instead rigged a ring-bolt in the center-top of the dish. I then passed a rope through the ring and loosely around the back-stay. I clipped the main halyard to the ring and hoisted away. The rope ring to the back-stay keeps the antenna away from the mast, so I hoist it just high enough to hang free between the mast and back-stay. Results were very good on Lake Ontario, receiving TV signals from across the lake. I give it a thumbs-up.
Interesting reading the Coast Guard report. I guess that I would think twice about watching TV while sailing in unknown waters. I have used a Shakespeare TV antenna for a couple years (dockside) and have had great results. I didn't want to mount it permanently on my mast, so instead rigged a ring-bolt in the center-top of the dish. I then passed a rope through the ring and loosely around the back-stay. I clipped the main halyard to the ring and hoisted away. The rope ring to the back-stay keeps the antenna away from the mast, so I hoist it just high enough to hang free between the mast and back-stay. Results were very good on Lake Ontario, receiving TV signals from across the lake. I give it a thumbs-up.
Any experts on RFI on this site?
Thanks to Bill for the great link, I wasn't aware of this problem. Very interesting. I'm about half-inclined to get one of the antennas listed and run my handheld GPS around it just to see if I can duplicate the problem. I'm wondering if there's anyone who's an expert on RFI (Radio Frequency Interference)in the group who can explain to me how this is occurring? While I understand that an active antenna could cause interference (in that it is essentially a broadband, low-power transmitter), wouldn't the antenna have been checked for that during FCC type acceptance? Does type acceptance even apply to an active antenna? And, due the large difference in frequencies for broadcast TV and GPS, one would have to figure this would be the result of at least third to fifth order harmonics, how could those be of sufficient energy to interfere with a digtal signal from a GPS satellite, especially at a range of two thousand feet? Wouldn't there be a low-pass filter on the output of the amp? Or, is it possible this is the result of some type of circuit failure in the antenna pre-amp itself? I know this question probably earns me a techno-geek badge, but I've been a ham for a long time and once in a while we get the joy of dealing with similiar problems, so I really hope somebody else into this stuff at a higher level than me can provide an explanation. At least I have a great discussion topic at next months Ham Club meeting! Jeff
Thanks to Bill for the great link, I wasn't aware of this problem. Very interesting. I'm about half-inclined to get one of the antennas listed and run my handheld GPS around it just to see if I can duplicate the problem. I'm wondering if there's anyone who's an expert on RFI (Radio Frequency Interference)in the group who can explain to me how this is occurring? While I understand that an active antenna could cause interference (in that it is essentially a broadband, low-power transmitter), wouldn't the antenna have been checked for that during FCC type acceptance? Does type acceptance even apply to an active antenna? And, due the large difference in frequencies for broadcast TV and GPS, one would have to figure this would be the result of at least third to fifth order harmonics, how could those be of sufficient energy to interfere with a digtal signal from a GPS satellite, especially at a range of two thousand feet? Wouldn't there be a low-pass filter on the output of the amp? Or, is it possible this is the result of some type of circuit failure in the antenna pre-amp itself? I know this question probably earns me a techno-geek badge, but I've been a ham for a long time and once in a while we get the joy of dealing with similiar problems, so I really hope somebody else into this stuff at a higher level than me can provide an explanation. At least I have a great discussion topic at next months Ham Club meeting! Jeff
Location! Location! Location!
The previous owner installed a Seawatch on the masthead. Reception is fairly good, but lower channels were less than perfect and ghosting was a problem. I moved the boat to another location in the marina and reception went down the tubes. I installed a better amplifier and reception improved a bit but the ghosting increased exponentially! If your slip is lower than the surrounding structures, forget it. As for the GPS interference problem, do you use your antenna when you navigate? Most of us don't! Just route the antenna power through a simple switch and turn it off! Works for me!
The previous owner installed a Seawatch on the masthead. Reception is fairly good, but lower channels were less than perfect and ghosting was a problem. I moved the boat to another location in the marina and reception went down the tubes. I installed a better amplifier and reception improved a bit but the ghosting increased exponentially! If your slip is lower than the surrounding structures, forget it. As for the GPS interference problem, do you use your antenna when you navigate? Most of us don't! Just route the antenna power through a simple switch and turn it off! Works for me!
Check out Terk
Here is a product that I have found to be interesting. Easy to mount/store and it is suppose to work well. I have not personally used one either. Specifically the TERK55 http://www.terk.com/
Here is a product that I have found to be interesting. Easy to mount/store and it is suppose to work well. I have not personally used one either. Specifically the TERK55 http://www.terk.com/
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