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Old 02-10-2009, 09:40   #1
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SSB Vertical Whip (or Not Vertical?)

Just started this thread to continue a discussion on whether a SSB whip needs to be vertical rather than hijack another thread.

S/V Jedi: SSB: lower support on hull and upper support on post; the whip must be perfectly vertical, not macho angled aft. The feed wire from tuner to whip very short, like 3'

Wotname: Sorry but I gotta ask, why perfectly vertical?

S/V Jedi: Because when you "slope" it, it becomes directional. On a boat, the primary antenna should be as omnidirectional as possible and this is where the long whip can gain an advantage over an insulated backstay.
This whip is called a "vertical antenna" which logically implies that it should be mounted vertical.

Wotname: I have to argue differently.
All whips are directional regardless of angle to the surface of the earth. There is very little emission from the end of a whip. Perhaps you are referring to polarization; if so, then as the principle method of HF propagation is the skywave, an angled polarization gives more opinions of the RF being reflected by the ionosphere. In fact after a couple of bounces, the polarization is all over the shop so it doesn't make much difference how it started.

You might notice many military vehicles with their long HF whips pulled right down into an arc. This gives a range of polarization angles for optimum skywave propagation.

Lastly, all vessels pitch and monos also roll so no whip stays very vertical when used at sea.
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Old 02-10-2009, 09:51   #2
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Most HF aerials on a warship are wire, and are at a slope of about 20-30 degrees.

Personally I would strat with an angle that looks aesthetically pleasing with the design of the vessel, and then see what works.
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Old 02-10-2009, 15:25   #3
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Quote:
Originally Posted by Talbot View Post
... Personally I would strat with an angle that looks aesthetically pleasing with the design of the vessel, and then see what works.
I know that Talbot would agree that it's often wise to start at the beginning - then move on to other (more advanced) strategegies, such as "strating", et al.
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Old 02-10-2009, 15:43   #4
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Originally Posted by Wotname View Post
All whips are directional regardless of angle to the surface of the earth. There is very little emission from the end of a whip.
You mean they are directional because they don't radiate directly up into space? That's not the definition of directional or omni-directional. Your masthead VHF antenna radiates in a donut-shaped pattern without radiating directly up to space but it sure is an omni-directional antenna!
See Omnidirectional antenna - Wikipedia, the free encyclopedia for reference.

A marine HF whip as sold by Shakespear is just a wire held inside a fiberglass rod. It is supposed to be mounted exactly vertical, not in any "aesthetically pleasing" orientation.

Quote:
Perhaps you are referring to polarization; if so, then as the principle method of HF propagation is the skywave, an angled polarization gives more opinions of the RF being reflected by the ionosphere. In fact after a couple of bounces, the polarization is all over the shop so it doesn't make much difference how it started.
Traffic amongst cruisers uses groundwave often because on higher frequencies they are in each others skip zone.

Quote:
You might notice many military vehicles with their long HF whips pulled right down into an arc. This gives a range of polarization angles for optimum skywave propagation.
Ah, but that is done for something completely different: NVIS (Near Vertical Incidence Skywave). This is done for short-range HF communications (30-400 miles) or when the car is in mountainous terrain. A vertical has a low radiation angle so it needs clearance around it. On a boat, this is not an issue so it should be vertical!!
You can read about this plus a nice photo here: Near Vertical Incidence Skywave - Wikipedia, the free encyclopedia

Here's a nice Dutch Willys jeep in mint condition showing the proper orientation: http://upload.wikimedia.org/wikipedi...illys_jeep.jpg

Quote:
Lastly, all vessels pitch and monos also roll so no whip stays very vertical when used at sea.
Nothing is perfect on a boat, the same thing happens with the other antenna's. But that doesn't mean one should make it even worse by not putting a vertical antenna vertical to start with.

So, a marine SSB whip antenna is an omni-directional antenna and should be installed vertical.

cheers,
Nick.
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Old 02-10-2009, 15:48   #5
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Quote:
Originally Posted by Talbot View Post
Most HF aerials on a warship are wire, and are at a slope of about 20-30 degrees.
Indeed, but those are long wire antenna's and not vertical whips. They are also highly directional. Pls. don't try to imitate those with your whip!! ;-)

Quote:
Personally I would strat with an angle that looks aesthetically pleasing with the design of the vessel, and then see what works.[/
Yep and you're not alone. It'll even work better in some directions, but it'll work worse in other directions. Why not angle your VHF whip too? both are end-fed mono-poles!

cheers,
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Old 02-10-2009, 18:08   #6
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HF aerials are a compromise by the very nature of metal rigging etc. Mounting on the stern with rack away from the rigging will give good results. Keeping the length of wire as short as you can from the tuner unit i.e mount as near as you can to the aerial (& if a metal hull spaced off ) will result in good results. The very nature of SSB has such a gain over the old AM transmitters allows for better over all coverage. The shortest earth length from the tuner is important as the aerial current is also flowing in this circuit & it will form a part of the radiating element. (i.e.the same current flow as the aerial on the external of the boat)

Regards Bill
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Old 02-10-2009, 20:33   #7
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As you can see in this photo…..I need to angle my antenna to allow for boom swing

Speaking with AsiaNet from the Philippines, people tell me I am transmitting very well, so I have had no reason to be concerned.

I agree with Bill, the distance between the tuner and antenna is the more critical installation issue.

On SG, my tuner is mounted inside the lazarette directly behind the antenna with about a 16 inch connection.
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Old 03-10-2009, 01:34   #8
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Quote:
Originally Posted by GordMay View Post
I know that Talbot would agree that it's often wise to start at the beginning - then move on to other (more advanced) strategegies, such as "strating", et al.
My keyboard has been soundly admonished for its tendency to arrange lettres in the wrong order.
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Old 03-10-2009, 09:39   #9
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Quote:
Originally Posted by s/v Jedi View Post
You mean they are directional because they don't radiate directly up into space? That's not the definition of directional or omni-directional. Your masthead VHF antenna radiates in a donut-shaped pattern without radiating directly up to space but it sure is an omni-directional antenna!
See Omnidirectional antenna - Wikipedia, the free encyclopedia for reference.
We might have to agree that we disagree . I take the 3D approach and you the 2D approach. Its different but no harm done.
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Originally Posted by s/v Jedi View Post
Traffic amongst cruisers uses groundwave often because on higher frequencies they are in each others skip zone.
Hmm... guess we operate in different parts of the world. Almost all HF marine coms in Oz will be skywave. Have a look at the locations of VMW & VMC see Marine Radio & Satellite Communications Services
If it isn't skywave, it isn't on!
As for groundwave, this travels along (or in) the ground / water as does not equate to a line of sight skywave so even with 2D, omnidirectionality is not so important. As you reference, short range HF can be obtained with NVIS.

I don't disagree that a vertical whip is good but I don't believe it is necessarily important to have to have it perfectly vertical. I would choose an angle that suits the installation and the boat; especially given that most times it will be pitching and rolling when used.
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Old 03-10-2009, 09:56   #10
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Quote:
Originally Posted by s/v Jedi View Post
Indeed, but those are long wire antenna's and not vertical whips. They are also highly directional. Pls. don't try to imitate those with your whip!! ;-)
Well yes, they different configurations but they are trying to achieve the same result i.e. HF communications. Unless you are referring to dipoles, end feed long wires and whips are similar (in the sense of polar diagrams) so if one works inclined, so will the other and vice versa.
Quote:
Originally Posted by s/v Jedi View Post
Why not angle your VHF whip too? both are end-fed mono-poles!....
Because the VHF is line of sight (without refraction by the ionosphere) and therefore directionally and polarization becomes important to establish a path. HF (skywave) is also line of sight until refracted (in varying amounts) by the ionosphere (and ducted by the earths surface) and thus the path is established by factors other than only directionally and polarization. HF (groundwave) travels along (or in) the surface of the earth (including water) and is not so effected by polarization (IIRC).

Opps... apologies to the non-engineering reader. If this bores you, go sailing and let my mate Nick and I slug it out together.
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Old 03-10-2009, 10:27   #11
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Sorry, guys, but I gotta agree with Nick on this one.

If the aim is to obtain omnidirectional performance (same signal strength in all azimuthul directions), then vertical antennas need to be vertical. This is true whether you're talking about HF, VHF or even UHF and higher (think cellphones).

Sloping antennas generally favor radiation in the direction of the slope. Often, one is constrained on a small sailboat, so the only practical multi-band antenna is an end-fed backstay. This "wire" slopes in a aft direction, so this tends to favor radiation off the back of the boat, to the detriment of radiation in other directions. Yes, of course, the mast and rigging on a sailboat affect omnidirectionality (as well as the sloping backstay), but this can't be helped.

"Ground waves" generally pertain to signals directly from the transmitter to the receiver, traveling near the surface of the earth. On HF frequencies, this is for short distances.

NVIS is a technique used for very short distance contacts, using low HF frequencies and skywave -- bouncing up and back. The NVA used it extensively in Vietnam to communicate from one mountain valley to another. NVIS takes advantage of the fact that the angles at which RF will be reflected back to earth from the ionosphere -- and not lost by passing thru it into space -- are greatly influenced by frequency. Low frequencies are bounced back at very acute angles, where higher frequencies hitting the ionosphere at the same angles would be lost.

BTW, most times whip antennas layed forward on military vehicles are not for NVIS communication, but for the very simple reason of securing the whip antenna so it doesn't whip about or hit low obstructions. It's generally released to a vertical position when actually in use.

The vertical angle of propagation -- not the same as "polarization" -- is very important. With very high angles (like NVIS), short-distance contacts can be made. For long-distance contacts, radiation near the horizon (very low "takeoff angle") is desirable. That's why, e.g., vertical dipoles rigged close to the ground (or the deck on a sailboat) are great DX antennas: most of their energy is transmitted at very low angles to the horizon. This is a case where positioning the antenna is counter-intuitive. Normally, one thinks that the higher the antenna the better. Not so in the case of vertical dipoles. The lower the better, because when you raise them their takeoff angle increases and other lobes develop.

Polarization is said to be important for VHF and higher propagation. Personally, I've never found that to be so, i.e., not really important. Most times, you can't tell the difference. Most all marine VHF communications are vertically polarized. However, there's no problem at all communicating with boats or shore stations using a horizontally-polarized antenna (like a yagi or horizontal dipole), and you'd need a field strength meter to really see some difference. (Ask any ham who regularly communicates over 2 meters VHF with mobile stations using vertical antennas, using a horizontally-polarized yagi or other antenna).

Finally, what gives sea water such a strong advantage (and which is often misunderstood) is not that it's such a great RF ground or conductor of HF radio signals (it's not, except on the surface; deeper down, RF at HF frequencies is greatly attenuated in just a few inches of seawater) -- rather, that it's such a great reflector of the electromagnetic waves eminating from an HF transmitter. Great to bounce waves back and forth between the earth and the ionosphere.

Now, the techniques used to generate those electromagnetic waves on a sailboat -- using an "antenna" and some sort of "RF ground" or "counterpoise" -- is the subject of much fun and disagreement and strongly held opinions. I have mine, and often they diverge from the mainstream "experts" and pundits. But, here's where I butt out :-)

Bill
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Old 03-10-2009, 10:34   #12
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Thanks for this info Bill.
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Old 03-10-2009, 11:20   #13
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Wotname,

So, how do you communicate with a fellow cruiser who is nearby but just out of VHF range? And how about 2182 kHz?

For any NVIS effect, both stations must radiate straight up and use low frequency. It is not realistic to expect this as workable, plus you would have to tilt the whip to horizontal on both boats. If the other boat uses a backstay, it wouldn't work at all.

Quote:
I take the 3D approach and you the 2D approach. Its different but no harm done.
The real definition is that tan omni directional antenna's radiation pattern is the same in every direction of a 2D plane. Now, you can tilt that plane but for all-round work you want it to be the earth surface so the antenna must be vertical.

Bill: I used vertical polarization with yagi antenna's without trouble but this was at higher frequencies. It wouldn't be a problem for 2 meter band, would it?

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Old 03-10-2009, 12:03   #14
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Nick,

No, no problem at all. In fact, my 4-element VHF yagi is oriented vertically to "favor" marine VHF which I listen to frequently. It seems to have no adverse effect on 2-meter operation....might even benefit, because the mobile stations themselves and most repeaters are vertically polarized.

If it matters at all (beyond the theory)!

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Old 04-10-2009, 08:44   #15
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Looks like the whip is better vertical and thanks for the conversation!
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