I have a Beneteau 423 with split backstays that run from the deck to the mast head. Does anyone have any experience in fitting isolators to one backstay and using that as a randon wire antenna for an automatic tuner? Any concerns about the uninsulated backstay resonating and absorbing power?
SSB ANTENNA ON SPLIT BACKSTAY
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Split backstay or twin backstay?
Sta-loc makes insulators which have the option of screw in forks or eyes to suit your rigging situation. If you have twin backstays, it might be convnient to see if you can use one insulator at the top and load them both up. If your boats rigging is bonded, you will need to insulate the lower ends too or break the bonding somehow. Like Gord says, you will need to isolate any section or inside parts which might be touched by the crew with plastic tubing or similar. You might find some feedback problems using only one side. My friend in Mexico has always had a problem with this on his ketch rig. He has a feed wire connected to his insulated triatic stay which runs up the inside of his wooden mast. I suspect the stays are a feedback path back to his computer and packet controller. I do not think that you really need 32 feet of wire but generally the more the better. The tuner should load up much shorter antennas but that depends on a lot of factors which I do not know from here. I would look for someone having the same or a similar boat who has done this already and ask them if you can. Walking the docks and taking pictures is good research too.
Sta-loc makes insulators which have the option of screw in forks or eyes to suit your rigging situation. If you have twin backstays, it might be convnient to see if you can use one insulator at the top and load them both up. If your boats rigging is bonded, you will need to insulate the lower ends too or break the bonding somehow. Like Gord says, you will need to isolate any section or inside parts which might be touched by the crew with plastic tubing or similar. You might find some feedback problems using only one side. My friend in Mexico has always had a problem with this on his ketch rig. He has a feed wire connected to his insulated triatic stay which runs up the inside of his wooden mast. I suspect the stays are a feedback path back to his computer and packet controller. I do not think that you really need 32 feet of wire but generally the more the better. The tuner should load up much shorter antennas but that depends on a lot of factors which I do not know from here. I would look for someone having the same or a similar boat who has done this already and ask them if you can. Walking the docks and taking pictures is good research too.
J
Joe
423 Owners Group
There is a great 423 owners group located at Yahoo Groups Beneteau423. Try it out. There's a wealth on information on the site. Good Luck
There is a great 423 owners group located at Yahoo Groups Beneteau423. Try it out. There's a wealth on information on the site. Good Luck
SSB Antennas
The traditional guidelines for a Backstay Antenna are to have the bottom insulator 7' off the deck, and 3' down from the masthead. Insulated sections of backstays longer than 35' are not necessary, however a longer antenna may perform better. The RF output from the tuner can be as high as 5000 volts at very low current, and grabbing the uninsulated part of an antenna while the radio is transmitting, can cause a serious RF burn - or could even be lethal! Therefore the bottom insulator is usually put 7' off the deck for safety reasons. If the bottom insulator is to be mounted at deck level, the backstay must be insulated from possible contact with crew, by putting an insulating material over the backstay, turnbuckle, etc. The best material is teflon tubing which has very good insulating properties, however the tubing must be installed on the backstay when the backstay is being fabricated by your rigger. A distant second best material is white nylon "snap on" shroud cover products available in chandleries. Attention must be paid to items such as bonding system wires, that may be attached to the backstay chainplate(s). Also note that a bottom insulator will have to be installed above a hydraulic adjuster (if fitted). Wavelength (in Feet) = 936 / frequency in MHz or wavelength (in meters) = 300 / frequency in MHz Although Automatic Tuners do a great job of adjusting fixed antenna lengths to varying frequencies, most antennas are designed for 1/4 or 1/2 wavelength, at some preferred frequency. Insulating a backstay can be expensive depending on what type of rigging you have, wire rope, rod or as on some race boats spectra, kevlar or technora. The cost of installing insulators sometimes leads people to use a standing whip antenna instead. The whip is tried and true and will do the job you require There are whip antennas specifically made for SSB use (23' or longer). Marine SSB Single Sideband Simplified ~ by Gordon West Goto: http://www.icomamerica.com/marine/ssb_book.asp Chapter 9 - Antennas: “... On a split backstay, where the split is below the masthead, use three (3) insulators. The to & bottom insulators are installed on the side of the backstay to be used as an antenna. The other insulator should be paced near the top of the split leg, as close to the Y as possible. This effectively takes the split out of the antenna system. Run the GTO15 up the stay, to a point above the lower insulator (about eye level) ...” SGC HF User's Guide: http://www.sgcworld.com/ftp/Books/hfguide.pdf
The traditional guidelines for a Backstay Antenna are to have the bottom insulator 7' off the deck, and 3' down from the masthead. Insulated sections of backstays longer than 35' are not necessary, however a longer antenna may perform better. The RF output from the tuner can be as high as 5000 volts at very low current, and grabbing the uninsulated part of an antenna while the radio is transmitting, can cause a serious RF burn - or could even be lethal! Therefore the bottom insulator is usually put 7' off the deck for safety reasons. If the bottom insulator is to be mounted at deck level, the backstay must be insulated from possible contact with crew, by putting an insulating material over the backstay, turnbuckle, etc. The best material is teflon tubing which has very good insulating properties, however the tubing must be installed on the backstay when the backstay is being fabricated by your rigger. A distant second best material is white nylon "snap on" shroud cover products available in chandleries. Attention must be paid to items such as bonding system wires, that may be attached to the backstay chainplate(s). Also note that a bottom insulator will have to be installed above a hydraulic adjuster (if fitted). Wavelength (in Feet) = 936 / frequency in MHz or wavelength (in meters) = 300 / frequency in MHz Although Automatic Tuners do a great job of adjusting fixed antenna lengths to varying frequencies, most antennas are designed for 1/4 or 1/2 wavelength, at some preferred frequency. Insulating a backstay can be expensive depending on what type of rigging you have, wire rope, rod or as on some race boats spectra, kevlar or technora. The cost of installing insulators sometimes leads people to use a standing whip antenna instead. The whip is tried and true and will do the job you require There are whip antennas specifically made for SSB use (23' or longer). Marine SSB Single Sideband Simplified ~ by Gordon West Goto: http://www.icomamerica.com/marine/ssb_book.asp Chapter 9 - Antennas: “... On a split backstay, where the split is below the masthead, use three (3) insulators. The to & bottom insulators are installed on the side of the backstay to be used as an antenna. The other insulator should be paced near the top of the split leg, as close to the Y as possible. This effectively takes the split out of the antenna system. Run the GTO15 up the stay, to a point above the lower insulator (about eye level) ...” SGC HF User's Guide: http://www.sgcworld.com/ftp/Books/hfguide.pdf
I have seen backstays w/o a lower insulator
No direct personal experience with such an installation but the guy was an experienced professional RF engineer. His radio works quite well. He has an APRS (automatic position reporting system) installed on his two meter radio. I was able to go on line, enter his call sign, pull up a chart, and zoom in to his position. Then I went to another link and pulled up a satellite picture and zoomed in to see his boat at anchor just a few miles away. We discussed his installation at length and I would trust his judgement. You should obviously insulate the stay from direct crew contact. I did once have a small RF burn which took years to finally resolve itself but that happened when working on the innards of a final amplifier not on an antenna which I would not expect to be so bad. Also, it was more than 40 years ago and was a vacuum tube amplifier. 5000 volts is a bit misleading in that while it is theoretically possible, it is also unlikely that you will encounter those conditions. In theory, a cell phone will do that too but they are not lethal except in some popular internet folklore. I have never heard of a lethal incident from a 200 watt transimtter. Have you Gord? My concern would be more from the secondary consequences such as someone getting a small shock and falling overboard. Clearly that is not good either but not quite so dramatic a story. A bigger issue than that might be if you were transmitting when a wave comes over the transom and the salt water effectively shorts the antenna when it contacts the water. That seems like an unlikely set of conditions too.
No direct personal experience with such an installation but the guy was an experienced professional RF engineer. His radio works quite well. He has an APRS (automatic position reporting system) installed on his two meter radio. I was able to go on line, enter his call sign, pull up a chart, and zoom in to his position. Then I went to another link and pulled up a satellite picture and zoomed in to see his boat at anchor just a few miles away. We discussed his installation at length and I would trust his judgement. You should obviously insulate the stay from direct crew contact. I did once have a small RF burn which took years to finally resolve itself but that happened when working on the innards of a final amplifier not on an antenna which I would not expect to be so bad. Also, it was more than 40 years ago and was a vacuum tube amplifier. 5000 volts is a bit misleading in that while it is theoretically possible, it is also unlikely that you will encounter those conditions. In theory, a cell phone will do that too but they are not lethal except in some popular internet folklore. I have never heard of a lethal incident from a 200 watt transimtter. Have you Gord? My concern would be more from the secondary consequences such as someone getting a small shock and falling overboard. Clearly that is not good either but not quite so dramatic a story. A bigger issue than that might be if you were transmitting when a wave comes over the transom and the salt water effectively shorts the antenna when it contacts the water. That seems like an unlikely set of conditions too.
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