[AK-VHF] Fw: [FFMA] Salt water gain

Wed Jul 10 16:52:32 EDT 2019

Paul,

Excellent information, and I recommend looking 
over W7GJ website for other info.  The VE7BQH 
antenna analysis tables have long served as a 
basis of comparison and for good gain and 
performance data such as stacking distances and 
G/T ratings.  The later is most important for those doing eme.

I had advice from YU7EF and that lead me to buy 
two G0KSC LFA yagis for my new 6m array.  Mine 
are mounted in Horizontal pol at 33-feet above 
ground which is about 1.6 wavelength.  EZNEC+ 
estimates that will provide ground gain at 8.4 
degrees above the horizon; YU7EF predicts first 
lobe gain of 20.88 dBi with free-space gain of 
15.75 dBi given by the manufacturer.  My soil is 
typical Alaskan glacial gravel/sand so I expect 
ground-gain will be lower.  Land is level 
tree-covered landscape.  Salt water is two miles 
west so do not expect any enhancement from it.
http://www.kl7uw.com/6m.htm

My single 6-element yagi at 20-foot (1 
wavelength) had g-g peak at about 9-11 degrees 
which was needed to hear 6m eme signals.  New 
array should be 4-5 dB stronger as new antennas have more free-space gain.

Still working on fixing azimuth drive system on the new array so not yet QRV.

For terrestrial VHF+ antennas getting above 
tree-tops is important.  In much of AK that will 
be about 50-ft.  MY 2m-eme array center is 
52-feet above ground (7.6 wavelength) and I see ground gain around 5-degrees.

Faraday will be problematic for 6m-eme; hoping extra gain will help a little.

73, Ed - KL7UW

At 10:26 AM 7/10/2019, Paul Kiesel via ak-vhf wrote:
>  Folks, I don't usually forward information 
> like this, but this email sent by W7GJ explains 
> a lot about how things like ground gain versus 
> height of antenna versus polarization of the 
> antenna affect antenna performance. Folks 
> interested in weak signal DX pay close 
> attention to these factors. For your reading pleasure.
>73,Paul, K7CW / VE7IBAVG Contest Guy
>
>    ----- Forwarded Message ----- From: 'Lance 
> Collister, W7GJ' w7gj at q.com [FFMA] 
> <FFMA at yahoogroups.com>To: 
> "FFMA at yahoogroups.com" 
> <FFMA at yahoogroups.com>Sent: Wednesday, July 10, 
> 2019, 4:52:14 PM UTCSubject: Re: [FFMA] Salt water gain
>  Hi Dwight,
>
>There is some introductory information about 6m 
>ground gain on my web page here:
>
>http://www.bigskyspaces.com/w7gj/6mTable.htm
>
>A hortizontally polarized yagi looking out over 
>calm salt water has ideal ground
>gain, as much as 6 dB at certain 
>elevations.Â  The elevations of the ground gain lobes
>depends on the height above the water. If the 
>yagi is one wavelenght above he water,
>the lobes are broader and higher. If it is far 
>above the water, the lobes will be
>more frequent and lower. The more distant 
>terrain will determine the existence/gain
>of lower ground gain lobes, and the closer 
>terrain is responsible for higher lobes.
>
>On my 6m EME DXpeditions, where the antenna has 
>directly looked looked out over
>unobstructed water on the distant horizon from 
>heights greater than 4 wavelengths, I
>have seen ground gain lobes down to negative 1.5 
>degrees due to the curvature of the
>earth. If there is land on the horizon, you 
>don't get those lobes around 0 degrees
>elevation, but you can still benefit from good 
>ground gain on the higher lobes.
>
>I have found that vertically polarized yagis 
>have higher ground gain lobes compared
>to horizontally polarized yagis at the same 
>elevation.Â  The ground gain of vertically
>polarized yagis is typically around 3 dB less 
>than horizontally polarized yagis. For
>strong signal ionospheric propagation (which 
>rotates the polarity around anyway),
>this doesn't matter much. For very weak signal 
>propagation (such as EME with a
>marginal system), it can make quite a difference 
>when you are aimed on the horizon.Â
>Of course if your antenna is elevated high at 
>the moon, there is no ground gain, so
>it really doesn't matter - you are then at the 
>mercy of Faraday Rotation to properly
>line up the polarity of the incoming signals with your antenna polarization.
>
>For terrestrial propagation, if the signals are 
>cross polarized, you can lose around
>22 dB by not having your antenna properly oriented. Since most 6 yagis are
>horizontally polarized (to try to take advantage of ground gain, and avoid
>interference from vertically installed masts, 
>feedline, etc.), you will be more
>successful with them if you are also horizontally polarized.
>
>If you are trying to activate a rare grid, you 
>probably want a horizontally polarized
>yagi with as much gain as you can get. If you 
>are trying to work the farthest, then
>height above flat terrain is important. I have 
>found that operation from uneven
>mountainous terrain is questionable in terms of 
>ground gain, due to the fact that the
>incoming signal's ground reflections are often 
>dispersed rather than being directed
>to the antenna. Of course, if you have a smooth 
>downward sloping open field without
>ground clutter in front of the antenna down to 
>the sea, you can have very good and
>low ground gain lobes.
>
>If all you are using is a whip on your car, the 
>gain should be better if you park by
>the sea (compared to parking in a parking lot or 
>a development), but you can't expect
>much gain when you start with such a small antenna.
>
>GL and VY 73, Lance
>
>
>On 7/10/2019 11:45:20, dwightjones at outlook.com [FFMA] wrote:
> >
> >
> > We know that signals are stronger when 
> operating next to salt water, but I don't
> > know how close I need to be to have 
> acceptable angles for reflection. Would a
> > person get the same effect a half mile from 
> the ocean while standing on a hill that
> > is several hundred feet high? What about ten 
> miles away and 5000 feet? What about
> > sitting next to the water with land a mile away on the other side of a bay?
> >
> > VHF operators say you must use horizontal 
> polarization, but HF ops say it must be
> > vertical. Are we talking about two different kinds of reflection?
> >
> > None of these questions are hypothetical for 
> me. I'll get a mobile whip and head to
> > Crescent City harbor if that will give me an honest 3-6 dB.
> >
> >
> > Dwight
> >
> > KO6FE
> >
> > CN71
> >
> >
> >
> >
>
>
>--
>Lance Collister, W7GJ(ex WA3GPL, WA1JXN, 
>WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ, 
>E6M, TX5K, KH8/W7GJ, V6M, T8GJ, VK9CGJ, VK9XGJ, C21GJ, CP1GJ, S79GJ)
>P.O. Box 73
>Frenchtown, MTÂ  59834-0073
>USA
>TEL: (406) 626-5728
>QTH: DN27ub
>URL: http://www.bigskyspaces.com/w7gj
>Skype: lanceW7GJ
>2m DXCC #11/6m DXCC #815
>
>Interested in 6m EME?Â  Ask me about subscribing to the Magic Band EME
>email group, or just fill in the request box at the bottom of my web
>page (above)!
>
>
>
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
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