Parasitic Possibilities

[dehler25]

I have a Shakespeare SSB fiberglass antenna mounted on the starboard stern quadrant and want to build an outboard lifting crane. The crane really needs a pole and it would be attached to the stern rail seat tubing. I have the room and it would be next to the outboard rail mount. What distance would I need to not create a parasitic element as the pole would be parallel to the antenna? It is difficult to separate them much in that configuration.

 

[Gunni]

Take the opportunity to get the antennae up higher by putting it on the stern pole you use to mount your motor lift. It sets you up with a location for other antenna, lights and radar.

 

[Don S/V ILLusion]

HF SSB antennas (not antennae) are substantially larger (longer) than practically mounted above a mast. Unfortunately, it's likely that any conductive material in the same plane will parasitically interact regardless of distance (boat length). At HF, antennas are designed with parasitic interactive elements as far away as 20 ft or more in some cases to optimize directivity (the antithesis of what you want to do).

Without rather complex antenna modeling, it's a 'crap shoot' how such interaction may affect the radiation pattern in strange ways or characterisitc impedence. It may be unnoticeable or it may be such that the load impedance of the antenna is so affected as to limit transmit power output and effective radiated power.

In other words, get as far away as practicable.

 

[Bill Roosa]

You certainly DO NOT want to mount the antenna higher up as it requires a ground plane (the water). Most boats have real problems with this in the first place and moving it further away from the water will not increase your range.
As for interactions with the rest of the metal lying around the stern, there is so much interaction now you probably will not be able to tell the difference.

 

[dehler25]

I certainly would not relocate the SSB antenna as it would be significantly easier to get more creative with the hoist location. There is no shortage of stainless tubing in the surrounding area, but most is horizontal which should present a minimum of parasitic distortion. I was mostly concerned due to a vertical pole close to a vertical antenna!

 

[dehler25]

I have davits and in the process of modifying them to support a solar array and anything else that seems that would be a good location, but mounting a 23' antenna would be ill advised, now if it were 23" that would work well.