Ham Radio HF antenna

[stormalong]

Originally Posted by Spot

Hi Matt, with something like an OCF up a mast on a boat, does one still need to rig a counterpoise? I am a new HAM and never 'played radio' on a boat before. My current boat is also quite small so I am not sure how an inverted OCF would play with the mast height only being 24' above deck and me needing to rig something to capture enough wire in the hypotenuse of each triangle.

PS Just saw Brian's comments above too

Operating HF on a boat your size, getting enough wire in the air will be a challenge. An inverted V will work for you but I think you will be limited to 14 Mhz and higher frequencies. Getting an inverted V and feedline up probably means not operating while sailing. One of the great things about ham radio is experimentation. Antennas are cheap and easy to experiment with. Dipole antennas do not need a separate counterpoise.

Some people that are space constrained get good results with magnetic loop antennas. MFJ makes one. Many people built their own. Loops develop high voltages and need appropriately rated variable capacitors to work properly.

[Sailmonkey]

Originally Posted by Spot

Hi Matt, with something like an OCF up a mast on a boat, does one still need to rig a counterpoise? I am a new HAM and never 'played radio' on a boat before. My current boat is also quite small so I am not sure how an inverted OCF would play with the mast height only being 24' above deck and me needing to rig something to capture enough wire in the hypotenuse of each triangle.

PS Just saw Brian's comments above too

Our ocd is 37’7” and 30’8”.

I’ve got the long leg from the main masthead down the triatic over the mizzen masthead and down the mizzen topping lift. The short leg just gets lead to the bow pulpit with a short length of line when in use.

[ArmyDaveNY]

Following

[Spot]

Here is what I am using at home right now, 40m OCF 'new Carolina Windom' style. Wires are 41' and 25', upper balun is 4:1 air core and after the 10' drop is a 1:1 'ugly' balun. Next experiment is to get rid of the drop and move the 1:1 up to the 4:1 as I don't have this thing hung very high. No SO-239's or store bought baluns were harmed for this project.

[Sailmonkey]

Originally Posted by Spot

Here is what I am using at home right now, 40m OCF 'new Carolina Windom' style. Wires are 41' and 25', upper balun is 4:1 air core and after the 10' drop is a 1:1 'ugly' balun. Next experiment is to get rid of the drop and move the 1:1 up to the 4:1 as I don't have this thing hung very high. No SO-239's or store bought baluns were harmed for this project.

Dumb question.... why the 1:1?

I’m also a ham newbie

[Spot]

"Why the 1:1?"

Here is a snippet from the article on Ham Universe:



New Carolina Windom by K4IWL - Len Carson - Carolina Windom Project - New Version!
...
This more recent, New Carolina Windom,version has some very interesting characteristics as seen in the drawing above.
For one, the 4:1 Balun has been moved to the antenna radiator and is built into the center insulator. The other interesting feature is that the 10 feet of coax from the Balun is terminated in a choke or line isolator. I have fitted the 10 foot stub with PL-259 UHF connectors on each end. This allows the coax vertical radiator to be easily removed if desired.It is designed to hang vertically which is one reason why this antenna is so effective. The radiation pattern when using the vertical radiator combines both horizontal and vertical radiation components and lowers the effective angle of radiation getting more of your signal near the horizon.

This antenna is in use the world over by DX'ers and DX'peditions. In one Navassa DX'pedition, of the 33,000 QSOs made, more than 27,000 were accomplished with this antenna. The DX'pedition team also had a beam and verticals, but the New Carolina Windom was the antenna they used. Its reputation for excellent performance is so good that it served as one of the antennas in setting two 40 meter "mile-per-watt" world records of nearly 4,000,000 miles-per watt.

The antenna can be used without the vertical radiator but the radiation pattern will lose the low angle component and may make the antenna less effective. If the vertical radiator is removed then you should move the line isolator to the bottom of the balun.
...

[j.g.evans]

I have use an unmodified back stay as the SSB antenna on 2 boats for many years with good success. I attached to the back stay under the aft deck to get out of the weather.

I have also used an antenna simulator with a very complex model to compare the back stay open at the top and connected. Both couple into all the rigging, lifelines, and anything else conductive. Both are nice antenna at some frequencies with max radiation low. Both have very ugly patterns at some frequencies. I decided they are equivalent overall and I did not want to cut my rod rigging.

Re ground: In one boat I ran wide CU foil between the antenna tuner ground and the keel bolts. In the second I edge tack soldered 1' wide CU sheets and pressed them against the hull under an aft queen mattress. This created capacitive coupling to the salt water and a good ground. I did not have to worry about galvanic currents. This will work only if the hull is solid glass.

[Jim Cate]

This will work only if the hull is solid glass.

Why is that?

Jim

[j.g.evans]

Re: Why solid fiberglass. To create a capacitor you need two plates separated by a thin dielectric insulator. One plate is the salt water. The second plate is the CU sheathing against the hull. You want a high capacitance which is achieved with a large area and a thin insulator with a high dielectric constant. Solid fiberglass with a dielectric constant of 2 or more is better than a balsa cored hull which would be thicker and the balsa would have a dielectric constant close to 1. The reactance (think resistance) of this capacitor is 1/2piFC, where F is frequency and pi=3.14.

[transmitterdan]

It’s not so much the capacitance of balsa but it is also lossy thus wasting power. But even plain hand laid or chopped strand fiberglass is also lossy but not as bad as balsa.

The worst is honeycomb material because it has a lot of air with dielectric constant of 1.

Reliance on the hull to connect the tuner return to the ocean isn’t optimal. A nearby thru hull or an external grounding plate is more likely to give lower impedance and better performance.

[nofacey]

Steel hull - single insulator on bottom of backstay I feed the antenna lead to, tuner connected to hull by rudder (it was close, easy & submerged). Boomer boat all frequencies.
Biggest trick is ensuring you have a great power supply - many offshore boats fade after even short conversations. I use a DC-DC converter that boosts voltage into radio.
Keep converter away from radio, they can be noisy.

Next time I’d try skipping the insulator.
Try it, can’t hurt anything!

[Brian.D]

You should read some of the post over at this forum: Marine Electronics - Cruisers & Sailing Forums

1. don't need an OCF unless you plan to work all bands, then you still need a tuner.
2. single band dipole works better than any other antenna because it is tuned to the frequency you are working. no counterpoise needed.
3. alternate backstay is best choice. no need to mutilate your backstay. use the sea as your counterpoise.

Some may agree, some may not. JMHO