Gain vs takeoff angle.

Equipment Antennas
21

Picture might be a little misleading. Azymuth for Phoenix is 299deg, which is indicated at the bottom of the map. Antenna has strongest lobe on 10m to the side of horizontal wire so 90 deg from it. If my maths are correct difference makes 210deg, so 7 o’clock in simple terms. Of course you can position it for 1 o’clock too.

I practice, in the field we never get horizontal part of inv-L horizontal but sligtly sloping. This changes radiation sligtly, hence my suggestion for 7-7:30. When I say antenna pointing, I mean end of horizontal part of antenna wire.

73 Marek

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22

Ditto, a full wave horizontal loop, in my experience, is less susceptible to electrical noise than other wire antennas. Effectively dropping the noise floor 1 or even 2 s-points while the other signals stay as strong as they were on an antenna suffering noise. As always it’s the SNR that matters more than just the signal strength.

73 Ed.

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23

I have a 10/12/15m groundplane antenna that I use on a 6m pole (actually more like 5.5m since the top section broke off). The 3 radials are cut for 15m which act as the guys (there is a short length of nylon cord at the end of each as insulator) and there are links for each band in the radiator. It is easy to erect, works well on all 3 bands and is a simple way to get access to the three higher bands when on a summit. It’s not directional and it may not be the most efficient but it has got me many US QSOs with 3W of CW on 10m including Arizona.

One of my summer projects is to make a new one with a radial cut for each band to see if that is any better as I don’t want to risk breaking my current one as it works so well.

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24

Hello everyone,
Sorry for the delayed reply. The number (and quality) of replies have kept me busy with reading, and thinking.

I should have mentioned that I am thinking about 10m because it is behaving (and the SOTA challenge), and it is a band I am willing to experiment with since the antennas are smallish. I will, of course, have antennas with me that can cover lower frequencies. Probably an end-fed half wave cut for 40m, and a linked dipole. Backup and backup.

I also should have mentioned that I will be operating SSB, I am not yet capable of CW.

MM0EFI, thank you for the report. I contacted GM4JXP and have some details on the Moxon and Delta.

G8CPZ you do have a point. Though it would be fun to be able to hit W7A, leaving it up to chance is also most certainly less disappointing than actively trying and failing.

ZL1THH the feed point conundrum with Delta loops is fascinating. Collin M0MCX did a video modelling them, and if I recall his plots were different. Or maybe his were in line with this graphic, and I had another article which was contradictory. It seems that most people do feed 1/4 wave up from a corner, but I also know people who feed them at the top.

N6IZ I should pack a vertical, though I guess I could just use a dipole like an L. I have never operated on salt water, but I am aware of its magic.

K6ARK, I had neglected the half-square when reading the ARRL antenna compendia. Interesting design for sure. I may look at turning the endfed into a linked endfed to make this a possibility. Though, I am not wild about taking two masts.

SP9TKW this is a good pragmatic idea, but I am not usually this organised. Maybe I should be. I shall make sure I have good 20m options, and add 15m to the linked dipole.

G8CPZ I have not looked too much at the topology. From what I can see, it looks like the islands are going to be similar to Iceland, quite old fjord-like mounds 500-800m in altitude. And some violent crags like the northern coast of Scotland. Landscapes I know well, but will probably find chilly since I have been softening in the desert. I have very little experience with verticals in the field.

For now I shall continue reading, and continue to improve the antennas I already have.

Thanks,
Tobias KK7BCO/2M0TFF

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25

If you get the chance of working near the sea I suggest to investigate (invest in) a vertical antenna that doesn’t need a groundplane. In the end it is not so much about again as about take-off angle.

Tom Schiller, N6BT and who made the Force 12 antenna’s, did extensive testing with antennas near salt water. His Team Vertical won many contests.

Scott Anderson, NE1RD examined many antennas for his expedition and described this in the artcile “Antennas for 100 pound DXpeditions”.

You can easily do a vertical array near the sea provided you do not need wires on the ground. Since you’re talking about a beam may I suggest to have a look at the Force 12 Sigma 5 or the copy: TWA2010 (TransWorld Antennas). A badly copied manual for the Sigma 5 can be found online and togetter with the NE1RD document there is enough information to make a clone. I’ve got one up now and am happy with it.

Alternatively you can take a look at the documentation for the N6BT Bravo 5 that also can be found online.

At this moment I’m contemplating a manual adjustable antenna, the Force 12 Sigma 40-XK which works 40m - 10m.

There have been several reports of people using these vertical antennas when restricted by home owners association regulations and still happily work great distances. But by the sea they really shine.

Enjoy the trip, sounds like great fun.

73
John, ZL1MJL

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26

I’m no antenna expert so I pose my statements for a bottom-fed quarterwave vertical (like the Chameleon MPAS Lite I use) almost as a question.

I know that EM waves over water, especially salt water, helps the far-field radiation. But I read that a (good) ground plane profoundly changes the near-field for the better and the NF extends only in the order of one wavelength from the antenna. So, unless your antenna is very close to the water’s edge, you will still benefit by having an artificial ground plane such as a counterpoise.

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27

The antennas that I mentioned are shortened dipoles and a dipole doesn’t need a ground plane. Hope this helps,
73,
John, ZL1MJL

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28

John, how many of these antennas have you carried up and set up on top of a mountain ?

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29

Keep in mind that it’s a group of small islands in the middle of the North Atlantic, so there are strong winds almost all of the time. My advice would be to bring an antenna as simple as possible, i.e. vertical dipole, triple leg, linked dipole. I doubt that sota-compatible moxon beam or any loop antenna (delta, quad, oblong etc.) would stand the wind.

Ahoi
Pom

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30

Exactly my point (at post #18) - simple and robust. All this talk about optimizing directionality towards AZ, USA is all very well but not if the antenna breaks in the wind or gets blown away. Don’t forget the mallet!

31

Have been there. Strong winds and wet. Would focus on getting a mast up that will stay put. Vertical or efhw with 6m mast. Metal L-profile to hammer into the ground to fix the mast - not too short. On the summits the wind speeds are truly impressive.

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