K0GKJ – Just Another Ham
The New QTH – A Floating Shack

Boat QTH (radio location)

Well, kids, I’m finally getting my act together on the boat QTH. The antenna, feedline conduit and mast are now completely uninstalled at the condo, so until I get the boat equipment up and running, my only opportunity to get on the air is in the car and with my HT (handheld transceiver), meaning VHF (line-of-sight) only – no HF (long range) – unacceptable!

Turns out I’m only going to need one backstay insulator to ensure one of my two backstays (wire from the top of the mast to the deck at the stern, or back of the boat) is insulated from the rest of the rig. At the bottom end, it’s already isolated, so I got the best insulator I could find, made by Hayn Marine. It’s the only one that has a failsafe backup if the insulating material should ever fail. Since that backstay can be under significant stress, this is how you ensure a portion of the boat’s rigging is both an excellent antenna and strong structural member.

 Next, I needed to find some high voltage wire to connect the backstay (antenna) to my Icom AH-4 antenna coupler (tuner). I’ve had this tuner for years, and worked great in my station up north with a G5RV di-pole.

The advantage of this tuner is that I already have it, and it will tune 6M (50 Mhz).

The disdvantage (over the marine version, the AT-140) is that it only handles up to 120 Watts. This is fine for my ham radio as it only puts out 100 Watts, but most marine SSB (single side band) HF radios put out 150 Watts. Ideally, I’d like to use this tuner for both radios when I finally spring the cash for a marine SSB. We’ll see.

But back to the high voltage wire, this is needed since an end-fed wire, like a backstay antenna, can develop very high voltages at the people end (the cockpit of the boat). Two issues:

  1. gotta be able to handle up to 15,000 volts, and
  2. gotta protect folks that might be inclined to touch the backstay (antenna) while transmitting (ouch!)

You know how anything associated with the word, “marine” automatically commands a premium price? Well, instead of seeking to source this high voltage wire (designated GTO-15) from a marine radio supply house, I found some on ebay for cheap!

Turns out this is exactly the same wire used to connect high voltage sources to neon signs. Also called ‘tesla’ wire (tesla is actually a term used to define magnetic flux density or magnetic induction). An HF radio antenna inducing RF (radio frequency) fields in and about a people-occupied space (near-field effect with the capability of inducing RF burns, for you hams) needs heavily insulated wire capable of handling almost the same type of voltage and induced fields of a neon sign.

The best part? Tesla wire is a LOT cheaper than marine GTO-15, and it’s exactly the same thing!

Next, I needed copper “foil” (strapping) to connect the antenna tuner to the RF grounding shoe on the bottom of the boat.

Why copper foil? Well, copper is an excellent conductor, and flat 3″ wide foil is used since at RF frequencies, current tends to travel on the surface of a conductor, not inside (as you hams all know), and the more surface area, the lower the impedance of that conductor (a good thing). OK, so I have another cheapskate story about buying RF Ground copper foil… did I get it from a radio supply house? Nope. Got it from a roofing company.

And not just ‘cuz I’m a cheapskate, but I like to be nonconventional, and it makes for an interesting story, which is almost worth more than the cost savings.

As you may know, roofers use copper for various purposes, and they tend to use heavier stuff than the radio supply houses sell. Why is this important? Well, if you put copper strap into a corrosive salt water boat bilge, and its less than 10 to 15 mil thick, the stuff will actually tend to dissolve on you over time! Roofers use stuff called 16 ounce copper and up. The 16 oz stuff is 22 mil thick, and I can get the 22 mil stuff from a roofing supply house for the same or less than what I’d pay for 10 mil stuff ! Not a bad deal, considering how costly copper is.

So I got three 10 foot sections of 3″ wide strap, soldered together (by an expert) into a contiguous 30 foot strap, for less than $80 !  That’s a lot of copper, and maybe a bit overkill, but will last at least two lifetimes. Hopefully, I won’t need all thirty feet, but I’ll have it on hand.

Here is an interesting article if you’re interested in reading about the traditional installation of a marine SSB rig on a boat. It is a little different than a shoreside QTH, but in a salt water environment, you’ll never find a better counterpoise than good ole Mother Ocean!

73

Gene

K0GKJ

Advertisements

No Responses to “Boat QTH (radio location)”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: