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View Poll Results: HAM, Marine SSB, Other?
HAM only 21 10.66%
Marine SSB only 57 28.93%
Both 88 44.67%
Other (sat phone, etc. please specify) 33 16.75%
No long range communication device 25 12.69%
Multiple Choice Poll. Voters: 197. You may not vote on this poll

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Old 11-12-2007, 08:39   #91
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Sarcasm isn't useful or called for regardless of whether or not you agree. You might want to read the link I posted.
It is easy to confuse gain with radiation angle (in the case of verticals, what you called "Take-off angle") or beamwidth (what you describe as "concentration of energy") in the case of horizontal antennas which is what you are describing.

It sounds to me we are disagreeing on what these terms mean. AGAIN, my only purpose was to clarify my original point and not argue with anyone. If you want to discuss further, I'd appreciate it if you could do so politely.
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Old 11-12-2007, 08:43   #92
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As Eric says, gain is a function of concentration of energy in a given direction. And, over DX paths, it's also a function of the takeoff angle or the vertical angle of radiation.
I agree, antennas can certainly have gain. However, when it comes to the angle of radiation and DX propagation, let's not call this antenna gain. A well-aimed antenna pattern can reduce path attenuation, but this is not the same thing as antenna gain. It does have the same effect though; the available power is better concentrated in a useful direction.

Bill, I realize that you know this well, but I figured that since we are discussing antenna gain and related misconceptions, we should be extra-careful with the terminology. And in case anyone asks, an antenna does have the same gain transmitting as well as receiving.
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Old 11-12-2007, 08:59   #93
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A well-aimed antenna pattern can reduce path attenuation, but this is not the same thing as antenna gain. It does have the same effect though; the available power is better concentrated in a useful direction.
Paul,

Yes, of course that's right. That's why I used "gain" (in quotes) at the end of my post...should have used it throughout when talking about the effect of vertical takeoff angle.

As you note, though, it does have the same effect as gain. That is, both the transmitted and received signals are stronger than they would be with a higher takeoff angle.

So, you have antenna gain itself -- traditional usage -- PLUS stronger transmitted and received signals which are derived from a lower vertical takeoff angle resulting in fewer hops. Can we talk of "net gain", maybe?? "Total gain"?? "Relative Overall performance"??

All these are frought with difficulties of definition. Can anyone suggest a better term?

Bill
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Old 11-12-2007, 09:40   #94
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maybe "enhanced directivity" or "apparent gain" might be more descriptive or less confusing.
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Old 11-12-2007, 10:58   #95
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How about directive gain which is different from "normal" antenna gain. And in the case of directive gain, reciprocity is only fully realized when the received signal polarization is the same as the transmitting antenna's polarization. HF skywave signals can and do change polarization during their travel. This is one of the causes of fading.

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Old 11-12-2007, 11:28   #96
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Now we're talkin'!

While the term, "directive gain" is recognized and useful, for me it doesn't precisely capture the "gain" derived from low angle takeoff over DX paths. Yagis, for example, exhibit "directive gain" in their horizontal pattern of radiation, but unless they're very high they don't realize the benefits of very low angle radiation.

I actually like Illusion's term, "apparent gain" better, since it encompasses both "directive gain" and "low angle gain".

Hope this discussion isn't going too far afield for most readers. Didn't mean to hijack the thread.

Bill
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Old 11-12-2007, 17:45   #97
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I've never seen a refererence book for "sailboat antennas" what came up with any conclusion beyond "Your mileage will vary and there is no one solution that can be said to be superior on all boats."

That includes the ARRL antenna books, and Gordon West.

The variables of rigging and electrical interactions with the boat and all that other fun stuff simply ensure that on each boat, for each rig, something will work best. But you'll need careful test protocols, specific definitions of "best" for your purposes, and a good bit of hands-on testing in order to find out what's "best" for your boat.
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Old 11-12-2007, 22:14   #98
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The term y'all is lookin' for is Path Loss. Pass Loss is a far field effect that follows the inverse-square law. Polarization loss varies between 0 and 6 dB's. Multi-path loss (fade) can approach 100%. Space weather can also affect the propagation of HF signals.

In the MF/HF range the best DX omni antenna is the 5/8 wavelength vertical over saltwater. It has a lower radiation angle and gain over the vertical dipole.
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Old 12-12-2007, 01:08   #99
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The term y'all is lookin' for is Path Loss. Pass Loss is a far field effect that follows the inverse-square law. Polarization loss varies between 0 and 6 dB's. Multi-path loss (fade) can approach 100%. Space weather can also affect the propagation of HF signals.

In the MF/HF range the best DX omni antenna is the 5/8 wavelength vertical over saltwater. It has a lower radiation angle and gain over the vertical dipole.
Yes, but Path Loss is independant of the antenna. Is there a single term that covers antenna gain, polarization, pointing, which skip angle is used, and path loss?

Also, with respect to polarization mismatch, can't the loss approach infinite? I realize that in the real-world, all signals are at least somewhat elliptically polarized, but if you had an ideal vertical/horizontal, or clockwise/ccw mismatch, wouldn't the loss be huge?

For me, the insulated backstay antenna is good enough. I've got a good ground, and a tuner, and I like the mechanical simplicity and clean installation. I've already got too many lines and wires running all over the place, so the idea of adding more junk up there just doesn't appeal to me.
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Old 12-12-2007, 05:00   #100
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Believe it or not the term that covers everything related to end-to-end communications is referred to as "System Gain".

An electromagnetic field will excite the electrons in an antenna even if the field and the antenna are exactly perpendicular. This is a physical effect related to the electrons interaction with the changing electrical and magnetic fields. This effect should not be confused with the affect of polarization on photons.

I agree that an insulated backstay antenna is good enough for most sailors. However, I should note that my reference to the 5/8 wavelength vertical is a little inside joke of mine. You see, it turns out that the physical length of an uninsulated backstay on most sloop rigged cruising boats is 5/8 of a wavelength somewhere in the HF spectrum. So, by leaving out the insulators and feeding the backstay directly you end up with pretty good antenna.
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Old 12-12-2007, 09:15   #101
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In the MF/HF range the best DX omni antenna is the 5/8 wavelength vertical over saltwater. It has a lower radiation angle and gain over the vertical dipole.

In this context, radiation angle and what you can "gain" are not mutually exclusive. This discussion is probably getting too into the minutia of antenna performance and probably only serves to confuse people and gets us further off-topic.

If someone is still reading this thread interested in figuring out what type antenna to install, there are far too many variables on a boat to make any declarative statements about which is best.
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Old 12-12-2007, 09:55   #102
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Your Mileage Will Vary

Some choices: Gallery :: Constructing a Marine Dipole Antenna :: MarineAntennaChoices2
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Old 12-12-2007, 10:42   #103
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Do you remember CN8AK, Gregg or CN8CX, Jack, both of whom worked in Rabat in the last 70's?
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Old 12-12-2007, 10:47   #104
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Yes, absolutely. Greg was my neighbor and good friend. We collaborated on a lot of fun stuff. Jack and Becky were in Tangier, and have retired to Washington, NC. He was the VOA station director there.

Another ham who was there was Bill, KB2DJ, who was the last base commander at Kenitra. He sailed his 41' cutter home from there to Pensacola. Talked to him a couple of weeks ago on 20m.

Bill
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Old 12-12-2007, 11:37   #105
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I was "stationed" in DC during that time and we had a foreign service net on 20m weekly with those guys and one in Niger, Zaire and quite few other places. "Best" place I ever got to in the neignbrohood was Ft Lamey or whatever it's called now.
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