mast as antenna

[kickingbug1]

    can a mast be used as a radio antenna?

[DaveE]

Great question, especially if the "yes" or the "no" each come with an explanation.

[Joseph]

The short answer is "yes", but this needs explanation... I have used the entire aluminum mast as antenna and succeeded in completing QSO's (communications) /MM (marine mobile) with stations 500 - 2000 miles away using Ham (Radio Amateur) HF bands (30 and 40 meters). It was by no means an optimal antenna, but it did work! The mast was "tuned" to the desired frequency using an automatic coupler placed right at the base of the mast. The HF radio operated at 50 W max and RF grounding was to the water. The whole setup was powered by a 12 V battery. I was not only firing the mast but the entire rigging, as the mast was not insulated from the stays and shrouds. However, the stem and chainplates were not reaching the water line. My assumption is that the spreaders and shrouds were probably reducing the antenna efficiency while adding quite a bit of capacitance. On that experience I'd say that, with a similar setup and if not other antenna was available, it might be worth a try for SSB, but I would not bother for VHF.

PS.- If none of this makes any sense to you, let me know and I'll try to explain better.

J.

[Potcake boy]

Not having personal experience with this I can't provide much detail, but I do know that backstays are used as antennae with appropriate isolators.  Don't forget about galvanic corrosion issues if using your mast - could undermine some components that hold the whole darn thing up.  I had some cotter pins (supposedly stainless) from a reputable boat store that corroded to uselessness within months.  Luckily the boot held the clevis pin from falling out.

Ron

[Craig Weis]

Some of this antenna design is so parsmittity that even a non-straight 'snip' at the very end of the whip can affect the output. I think the power [wattage] needs to be at the very tip of the whip and adjusted with an SWR meter? At least in the old am CB days that was a concern. I really can't add much to this but I know its 'line-of-site so 25 foot is good for about 12 miles? About. Sorry no help. skip.

[Joseph]

The rigging-as-antenna experiment described above was not conducted in a CP-16 but in an Alberg 22. The boom was horizontal to the mast and not insulated at the goose neck and I was the first surprised to see that a rigging of aluminum and steel with boom, spreaders, two stays and four shrouds in place could not only offer any reception but had even some (albeit reduced) capacity to transmit!  Using a coupler of the kind of a Smartuner (I was using an SG-237) one can attempt connectivity in HF bands using pretty much any large and more or less linear piece of metal, provided it is insulated from the ground (Radio amateurs have even experimented with roof gutters). However, as has been said, best results for an HF (i.e., SSB) antenna in a sailboat have been obtained with a backstay insulated at both ends and loaded as an inclined vertical, from below, and using a coupler of the kind indicated. The problem is for a sailor to have the guts of having the backstay of his boat cut in order to install the insulators... I for one want my backstays intact! The other major problem and perhaps most important issue is to achieve a good RF grounding (different that the electric grounding).  In FG hulls this type of grounding is usually achieved via copper strips laid on the inside of the hull under the water line. These strips then couple as a capacitor with the surrounding water outside the hull. This is a must for any disbalanced (i.e., vertical) antenna but no required if using a balanced dipole antenna. RF grounding in a boat depends on the conductivity of the surrounding water and hence is much better if the hull is floating in salt water. In fresh water some of my best radio HF results from small sailboats were obtained without RF grounding using balanced antennas: a commercial "Buddipole" or a "Delta Loop".

J.

[kickingbug1]

   my main concern is to use a car radio in my boat---has anyone done this using the mast as an antenna?

[Joseph]

As long as you don't use it to transmit no harm can be made, so try it and let us know how it works!

J.

[Potcake boy]

   my main concern is to use a car radio in my boat---has anyone done this using the mast as an antenna?

If you already have a VHF antenna in use, you can get a splitter/filter from the boat store that allows use of your VHF antenna as an excellent antenna for AM/FM radio. Have used it myself with success.

Ron

[Citroen/Dave]

I ran my AM/FM/Weather Radio - antenna wire - from the bulkhead mount to an interior chain plate of a side stay.  Reception is great! Receiver only.

[Craig]

Re: Lightning protection. Not a good idea to have ungrounded mast/rigging. Hence the use of the backstay as an antenna. As mentioned a Smartuner(I have one) will TUNE just about any piece of metal. Radiation EFFICIENCY is another issue altogether! In a non-resonant antenna most of the power is dissipated in one form or another before being radiated by the antenna. A tuner just makes the transmitter see a resonant load. You might show 50W output but only a watt or two is actually getting radiated! An antenna cut to  a harmonically related length (1/2, 1/4, 1/8 wavelength, etc.) will radiate more efficiently than a random length in MOST cases.

[skip1930]

Waterline to Top-O-Mast is 25 foot on a CP-19.
The Shakespeare Antenna is 30 inches atop of that and isolated from grounding through the aluminum mast.

Shakespeare sells a box and lets the UHF ALSO becomes a am/fm antenna.

skip.