Aerial Installation

I’m a newcomer to r/c / Footy sailor with only 2hrs sailing time using a typical main + jenny rig in fairly light wind conditions.While no great problems have been encountered so far I’m well aware that things will change when stronger winds are encountered, It’s for this reason that I’m keen to try out a MacRig. One of my initial thoughts was how do I install an aerial - a fixed mast provides a near ideal mounting for an aerial whereas the moving stainless steel / carbon tube combination of a MacRig appears to pose problems. What advice can you experts offer in respect of an aerial attachment on a MacRig?

Philvin, there are a couple of considerations that come into play first.

Starting with the “fixed mast”, if it is a carbon fiber tube then you don’t want to run your arial along it. Carbon is conductive and will obstruct the signal.

I run my arial in a lightweight plastic tube attached to the inside surface of the deck. If your hull is carbon fiber then this is not an option for you for the same reasons mentioned above. However, if your hull is made from fiberglass, running the arial inside is doable as long as it is as high as possible in the boat. Water will also block the signal to some extent so you want the arial above the waterline.

If you want to have the arial outside of the hull I would have it exit the hull through a central location in the transom. I would then run it along the deck to the bow. Exiting through the transom would be the place least likely to take on water since the deck on a Footy is frequently awash.

The primary consideration in designing your r/c layout is to make sure that you have access to the gear and that it can be removed and replaced easily. In the US you will have five minutes between races to do any repairs. If you plan to race your boat, having a backup tray of r/c gear that you can quickly drop in will get you up and running efficiently. You can figure out what quit on you at the end of the day or event. Often the hardest part to swapping in new r/c gear is threading the arial, so some thought should go into how you arrange your system.

My primary R/C hobby is discus-launch gliders. While it is true that SOME carbon-fiber laminates hinder the transmission of RF signals, their use is actually not as common as a lot of people would lead you to believe. It takes a quite dense matrix of carbon to create a significant problem and most of the laminates available to us are not of that type. While I wouldn’t run my antenna INSIDE a pulltruded CF tube, typical of what we use, securing it to the mast shouldn’t cause a significant problem. I regularly run my antennas for my gliders INSIDE a wrapped CF boom (less dense than pulltruded) and have had no range problems even with gliders at over 1500 feet of altitude (measured with an altimeter).

The recommended plastic tube is of course a very good suggestion as well, and removes all possibility that your carbon will cause you troubles.

Here’s a question I have regarding this subject: For 2.4 Ghz receivers, I assume most are keeping the short antennas inside the hull - what effect does heel-over have on this arrangement when the receiver ends up close to, or below the waterline?

Simple, simple, simple.

Tape it under the deck. If you can’t feed it forward too well, put it in a straw, and move that forward. Then tape the straw to the deck. I’ve done this on most of my boats with no issues.

Many thanks to Niel, Allan Wright and Modelyacht for their comments which give me confidence in the belief that in the model boat world it is possible (and often necessary) to depart somewhat from the technical demands of radio transmission in a wider context e.g. transmit & receive aerials identically polarised (vertical / horizontal) ,mounted well above ground and matched in respect of directional properties etc. If I can safely install the aerial within the confines of a dry hull and operate at 200ft plus I’ll be happy - at that distance it becomes difficult to see a Footy let alone control it !

I note Niel’s warning against running alongside a Carbon Fibre tube, I think that this would be particularly relevant if the tube is likely to be ‘earthed’ (‘grounded’ in the US) by way of a wet deck or hull. I have in fact experimented with a Rx Aerial totally encased within a CF tube (not grounded) and the results were satisfactory but in practice such an arrangement might not match up to Niel’s wise advise re ’easy removal and replacement‘.

As has been pointed out Carbon Fibre is conductive, as such it should be possible to use this directly as the aerial component- has anyone tried this ?

I have measured the resistance of a typical carbon fiber mast, and it is not nearly low enough to use directly as an antenna. As someone else has said, there is too much plastic encasing the carbon, so it is a pretty good insulator. However, I have also wrapped the antenna around a steel guy wire on a Victoria, which would appear to be a terrible idea, and found that it worked perfectly well. But it may be related to the length of the guy wire, which just happened to be very close to 1/4 wavelength at the 72 mhz radio frequency.

My current Footies use the Mac rig, so it is convenient to just drag the wire in the water, or lay it inside the boat, but our pond is only 150 yards long.

Conclusion - Do whatever is convenient, but test it