SSB antenna question

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jim5099

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I’m considering installing an SSB transceiver, using the back stay as an antenna. Is it feasible to only fit an insulator at the top of the back stay ? This would simplify the connection of the cable from the transceiver as it could be connected to the chainplate inside the hull. I am aware that the backstay would be ‘hot’ when transmitting but feel that this risk can be controlled as there are only 2 of us on board.
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Rig some sleeving eg UPVC waste tube to stop the rare chance of someone holding on to the backstay whilst transmitting. I'm not enough of a radio buff to know if there might be other problems. Does the signal arc across to other bits of metal, like the pushpit?
 
as the signal feed will be at the chain plate moisture will effect the SWR so you will probably loose loads of power. Why not look at putting a wire on short insulated stand offs up the back stay.
 
michael_w said:
Rig some sleeving eg UPVC waste tube to stop the rare chance of someone holding on to the backstay whilst transmitting. I'm not enough of a radio buff to know if there might be other problems. Does the signal arc across to other bits of metal, like the pushpit?
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Yes it will arc across, treat it as you would a high voltage conductor. I'm not sure wet grp will stand the rf currents.

Ideally the bottom insulator should be above head height, don't forget you need to think about a ground plane, copper strip & a sintered bronze plate.
 
It is a profound question ie will you still be able to hear and be heard with the chain late as part of the antenna. If the antenna is not the best the transmitter will back off power to avert damage. If the tuning is affected by moisture the auto tuner will hopefully retune it. However antennae have always had decent insulators with long path over the surface to avert leakage. The concept of the GP hull being the insulator is a bit of a concern considering it moist likely to be wet and salty. Certainly no ideal.
I think I would go for an insulator at the bottom and a wire attached going to a feed through insulator into the hull. (just because that is always the way it is done.
Note however that ocean racing safety requirements call for a stand alone antenna (A whip antenna) which will remain useable with mast down. Perhaps you should also go for a whip ol'will
 
i just use a "ropetena" which is 35 feet of 10 awg tinned cable fed inside a bit of 10mm double braid with the center core taken out secured to an eye at the bottom and pulled up on a flag line to the top of the mast.
wire goes direct to the RF output through a deck gland and can be coiled up on the pushpit when not in use
the wire is a calculated length for wavelength so the tuner works at optimum,and is matched to the ground counterpoise
useful link here on antennas
http://www.cruiseemail.com/articles/HF Radio Installation Procedure for Marine Applications 16 Feb 2015.pdf

Rope Antenna With any antenna, the installation of a good counterpoise provides the greatest efficiency and maximum output from the transmitter and the Antenna tuner (whether a manual or auto tuner). The transmission line to the antenna should not be running parallel to any rigging and should be spaced at least 2-3 feet away. This practice prevents the effects allowed by vessels that have poor filters in the power supply of refrigerators and inverters. The power supply of these devices oscillates into the grounding system which ties to the ground side of the battery. This pulsing oscillates at such a high level that it is coupled into the antenna system of the vessel. When listening to the HF radio, this noise sounds like someone sending Morse code. (If you turn off these appliances the equipment the noise will stop. At the antenna tuner all that is needed is a flat copper ground strap 1 - 1.5 inches wide and no more than 0.130 thicknesses, going from the tuner to the Ground Plate. A DC Block should be inserted in the line from the antenna tuner to the ground plate. This stops the induced noise current from looping back through the antenna tuner to the radio, and reduces the noise caused by the loop. Summary For efficient and reliable H.F. communications it is extre
 
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It was possible to buy long stainless shackles, maybe 6mm, with a plastic sheave, it was about 12mm diameter, on the clevis pin. These were sold to be inserted in life lines to insulate the life lines. I never understood why you should need insulated life lines.

I inserted these devices at the top and bottom of our backstay (so the back stay was secured onto the little sheaves top and bottom and I used silicone to stop the sheaves moving from dead centre) and used an ICOM M800 without issue (crew were instructed not to touch the backstay during transmission). We used the keel as the ground plate. The SSB was accepted for China Sea racing from HK to the Philippines and the M800 continues to provide stalwart service in Oz.

Now we have fancy insulators top and bottom of a stay (or shroud), an equally fancy ground plate ( we no longer have a steel keel) and the M800 seems no better, or worse - for the investment. We do carry a spare aerial - just in case. The main and insulated aerial is carried from the deck in a fibre glass tube, sold as a batten by Blue Streak, which is clipped to the shroud with have duty cable ties - in case anyone grabs the shroud moving along the side deck.

I only used the M800 on RORC races and removed it for local HK racing. It came to Oz with us and I installed it myself, each time. Just follow the instructions - and then test it.

Jonathan
 
thanks for all the responses and references. Seems sensible to do it the standard way with 2 insulators rather than cutting the corner.
i hope that there will be others to talk to when I eventually get around to this ?
Thanks again to all.
 
jim5099 said:
thanks for all the responses and references. Seems sensible to do it the standard way with 2 insulators rather than cutting the corner.
i hope that there will be others to talk to when I eventually get around to this ?
Thanks again to all.
Click to expand...
check with your local riggers they often have serviceable second hand stay lok insulators,and make sure you do the calculation for the correct wire length of the section to be used as the antenna
 
"I never understood why you should need insulated life lines"
From the days of using RDF (radio direction finding) a loop of wire round the boat could lead to inaccuracies
 
atol said:
check with your local riggers they often have serviceable second hand stay lok insulators,and make sure you do the calculation for the correct wire length of the section to be used as the antenna
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I don't know why you would want a specific lenght of wire for antenna. Given that you will be using frequencies from 3 mhz up to 15 or more mhz. The antenna tuner (manual or auto) should be able to tune accurately. Indeed from my (large) experience of HF on small aircraft with manually set up then switched antenna tuner an antenna length near resonance for one channel was most difiicult to tune. We settled on 28ft as being ideal for frequencies 3.4mhz 6 mhz and 9 mhz. Long time ago using double sideband (AM) before SSB was made mandatory. ol'will
 
William_H said:
I don't know why you would want a specific lenght of wire for antenna. Given that you will be using frequencies from 3 mhz up to 15 or more mhz. The antenna tuner (manual or auto) should be able to tune accurately. Indeed from my (large) experience of HF on small aircraft with manually set up then switched antenna tuner an antenna length near resonance for one channel was most difiicult to tune. We settled on 28ft as being ideal for frequencies 3.4mhz 6 mhz and 9 mhz. Long time ago using double sideband (AM) before SSB was made mandatory. ol'will
Click to expand...
you are correct,the tuner will correct for most lengths except that there are a few lengths that you should avoid so worth doing a bit of research before cutting a random length
 
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