Backstay Antenna (RopeAntenna)

HF SSB, Halyard Rope Antenna

 

Background:

 

The JG-1 Antenna has been developed over the past 5 years by Dr. John Gregory, a RF designer, with a specialty in marine RF communications. The antenna has been tested successfully on many different sizes and models of vessels.

 

Concept:

 

The original idea was developed when the Swedish Whitbread team required an SSB/HF antenna that could be used during a race, with both minimal effort and high gain for reliable communications. The design immediately became very attractive to catamaran cruisers, as they have no backstay capabilities. The convenience and compactness of the JG-1 Rope Antenna has now become so popular that monohull vessels use it as either a backup antenna or as a replacement /alternative to a very costly insulated backstay.

 

Problems with Conventional Backstays:

 

Conventional backstays are installed by rigging companies that have little or no knowledge as to the necessary electrical RF design length for the backstay.

 

Almost all backstays are

 

 1. Cut entirely too short

 

 2. Omit the necessary second insulator at the top end on the backstay, to prevent skin RF effects when covered with salt from the air and ocean mist.

 

 3. Stainless stays are a poor conductor of RF energy.

 

 4. Cheap / poorly installed insulator can break loose under extreme torque, (during a rough passage). The backstay carries more weight and “g” forces then any of the other stays, so why risk altering it?

 

 The Alternative

 

The JG-1 Rope Antenna uses a strong Staystat halyard line manufactured by New England Ropes.

 

A precisely measured length of copper wire, with a tinned coat of silver nickel and an outside insulator is carefully inserted into the core of the halyard.

 

One of the key successes of the JG-1 Rope Antenna is that this precise length of wire floats inside the halyard, and thus is never being stretched, under any conditions. Even when the mast sways, only the halyard stretches, leaving the copper antenna line always the same precise and correct length. This means any antenna tuner will not be hunting for new RF resistance at the given frequency throughout the day due to the continual stretching of a stay or other antenna.

 

Design Criteria

 

There are 3 major variables that are necessary to the design of any antenna to work with all-major automatic antenna tuners on today’s market.

 

These variables for antenna matching are RF resistance, reactance, and good RF grounding for the antenna counterpoise.

 

Each model of the JG-1 Rope Antenna is precisely designed for the correct resistance and reactance for the length that will fit your boat, but the grounding you require inside your boat is equally important no matter what antenna you install.

 

Grounding:

 

The importance of taking the time and effort in the constructing of a good ground, and most importantly, in adding counterpoise radials to your antenna system cannot be overemphasised. .

 

After years of extensive testing, here is how we recommend addressing the grounding and counterpoise system for your vessel.

 

Normally, the antenna tuner is located in the stern lazarett or locker. It should be mounted in an area that is dry and easily accesible for maintenance. Maintenance to an tuner is making sure that the radiating terminal is always clean, the wires are not pinched, bent, and are free from other electrical, and control circuits cables that are near equipment, such as the auto-pilot control lines. 

 

The main ground lug on the tuner should be connected via a 1-2 inch copper strap, and within 5-7 feet of a ground shoe. This ground shoe should be a copper/ bronze plate mounted outboard. There should be NO other electrical lines connected to this plate from the inside, other than RF (radio) related electronics. This ground is the electrical ground return from earth ground, except that your earth ground is now the salt or brackish water.

 

From the same grounding terminal on the auto tuner you now layout the counterpoise lines for your antenna.

 

We recommend that 2 lines be constructed on both port and starboard under the floorboards, in the bilge area, below the water line.

 

These counterpoises become the reciprocal to the antenna that is above the deck and connected to the top of the mast or mizon.

 

The counterpoise lines for the antenna are connected to the grounding wing nut on the antenna tuner (the copper strip from your grounding plate / shoe also attaches here)

 

In the past 2 years, we have experimented using 450-ohm twin lead antenna line, which performed with outstanding results. The following is what we recommend:

 

Counterpoise:

 

The counterpoise lines for the tuner and antenna is twin ladder 450 ohm ladder line (a premanufactured counterpoise system is available from here at radios.net.au)

 

On one side of the vessel either port or starboard, we cut the ladder line at approximately 42-47 feet. This counterpoise has good RF resistance for frequencies in the low marine bands, which also support the amateur bands.

 

The opposite side of the vessel, again below the water line, the same 450 ohm ladder line material, is cut to 32 feet from the start of the autotuner. This line gives a good RF resistance and reactance to the auto tuner for the bands below 12 MHz.

 

It is best to have the lines on the port and starboard side separated by at least 4-6 feet.

 

This 450 ladder line should be any length from 32 to 27 feet for the one side of the ladder line and the second side of the ladder line is cut to 17 feet. This side supports the higher frequencies, from above 12 MHz.

 

Now the auto tuner feels comfortable as to tuning the JG-1 or a basic well-cut backstay.

 

A simple way to check the effectiveness of your installation (and that your antenna tuning is doing its job)  instrument to check the output of the antenna tuner is using a simple SWR meter. Simple does not have to be expensive and covers the entire HF bands.

 

You will find by adding the counterpoise and a good grounding system that not only will you lower the noise level of the radio, but also you will get better reception, more power output, and improved signal reports.

 

The JG-1 Halyard antenna works exceptionally well with the following tuners,

 

ICOM AT 120,130,140, Icom AH 2,3,4.  LDG, all tuners, SCG 230.

     2 Coils of ladder line, ready to install