Tilted SSB Antenna

[geoffschultz]

I was recently corresponding with an individual regarding reefing points and sent him a back-lit photo of the sails. While I was looking at it, I realized how much the whip SSB antenna is tilted backwards (about 10 degrees), and was wondering what effect that tilt would have.

I regularly use the SSB for e-mail via SailMail, with no problems. When I'm in the NW Caribbean, I'm a network controller and/or a weather guy for the NW Caribbean Net (which covers from Panama to the Gulf of Mexico), and people have always commented what a strong signal I have.

The tilt is due to the stand-off from the rail. I'm wondering if I'd have a better signal if I were to put a block at the base and make it vertical?

-- Geoff

 

[RanAweigh]

10 degrees isn't going to amount to a hill of beans. Remember the platform (your boat) is rolling and pitching more. The effect on either the transmitted or received signal is nil.

 

[geoffschultz]

10 degrees isn't going to amount to a hill of beans. Remember the platform (your boat) is rolling and pitching more. The effect on either the transmitted or received signal is nil.

In reality, we're at anchor the vast majority of the time that the SSB is in use. Hopefully we're not rocking or rolling that much!

 

[alexco38]

Tilted antenna

4-5000 Khz is not that critical as far as antenna orientation is concern. People use the backstay (with two insulators) as antenna to make it longer.

Unlike VHF-UHF or higher frequency, the radiation is not that much affected by the tilting. Although if you can size the length of the antenna to 1/4 or 1/2 of the wave length to reduce reflective wave called standing wave ration (SWR). You can buy a SWR meter to see forward and reflected wave.

 

[Bob Poff]

I wouldn't think it would matter at all.

With all the reflection from the mast and rigging, heaven knows what the actual perceived radiation pattern is as seen in the far field.

Antenna patterns don't act truely to theory until they're maybe a wavelength away from other objects (wavelength at 10 Mc = 30 meters, 7 Mc=40 meters)

 

[geoffschultz]

4-5000 Khz is not that critical as far as antenna orientation is concern. People use the backstay (with two insulators) as antenna to make it longer.

Very true! I had forgotten about the use of a backstay...The typical frequencies that I use are 6 Mhz for communication on the NW Caribbean net and 10-16 Mhz for SailMail during the day.

-- Geoff

 

[Snotter]

As a ham radio operator I have made many contacts using a horizonatally polarized antenna with people who were using a vertically polarized antenna. I suspect that 'skip' changes the polarization of an RF wave. Any hams out there who can verify or refute that statement?

 

[Ken Palmer]

A vertical antenna typically has a low angle of radiation. This means that HF will travel further before bouncing off the ionosphere, resulting in further communication distances. By tilting the vertical antenna, you are causing the radiation lobe to a higher (and lower) take-off angle. This results in better communication with other stations closer to you on the HF bands.

 

[geoffschultz]

A vertical antenna typically has a low angle of radiation. This means that HF will travel further before bouncing off the ionosphere, resulting in further communication distances. By tilting the vertical antenna, you are causing the radiation lobe to a higher (and lower) take-off angle. This results in better communication with other stations closer to you on the HF bands.

Of course that will depend upon which way the boat is pointing...

 

[windward54]

I use a Gam antenna. Goes up the backstay about 20 feet until it hits the split backstay, takes a funny twist to port and goes up another 15 feet, so talk about funny angles. But I seem to get a good signal out and never had a problem with communication, even when e-mailing.

 

[Don S/V ILLusion]

As a ham radio operator I have made many contacts using a horizonatally polarized antenna with people who were using a vertically polarized antenna. I suspect that 'skip' changes the polarization of an RF wave. Any hams out there who can verify or refute that statement?

This is one of those half-truths. The polarization doesn't really change but rather it loses some of it's vertical characteristic as it bounces off the various layers of the ionesphere effectively causing all waves to become predominantly horizontal over long skip distances.

Over the distances most of us use for marine HF communications, this isn't as significant as the loss you effectively obtain from cross-polarization losses.

Generalities are often not true so it can be misleading but more often than not, if I am using my vertical to communicate with another ham in europe as an example who is using a horizontally polarized antenna, the signals on both ends will be enhanced by either of us switching to obtain common polarization.

 

[Ken Palmer]

Further distance

Of course that will depend upon which way the boat is pointing...

That would be true; that is why I said "higher (and lower) take-off angle. You may have to swing your boat around to get further distance in the direction you want.