Necessary for Antenna to be higher than roof?
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| Feb 4th 2019, 13:25 | |
W4CWLTotal Topics: 0 Total Posts: 0 |
Hello all! First - apologies if this is covered extensively elsewhere in the forum. I was not able to find a relevant discussion using the search feature. I have a question about Yagi/beam, or even the W8JK antennas. Do they have to be above the roof line, or is it enough to get the elements above the brick? More details including photo link below. I live in an HOA, and the person who wrote the restrictions about antennas was very focused on satellite dishes, not on Ham antennas. There aren't any specific restrictions on towers or other short wave antennas. That being said, I could see a major fit being thrown if I don't do some due diligence beforehand. I have a location in my back yard where I think I could "hide" a tower, rather than just throwing it in the neighbor's faces by putting it up in my big back yard. Here's a link to a photo of my back yard so you can see what I'm talking about: https://share.icloud.com/photos/0XGEDfRa_0H5uc6fUsMELephA The area just behind the house, where they dug out the basement, could hold a small tower. I have a clear shot out the back yard, and if I get it just above the brick, it won't be visible, and I figure I could still shoot a signal that way too (due west). Ideally, I would put a 100foot tower up in my huge back yard, but that's not going to happen. I don't want to invest all the money in a tower and a beam if the propagation is going to be awful. Thanks! |
| Feb 4th 2019, 13:57 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
As a rule of thumb, you want a horizontally polarized beam for HF to be at least a half wavelength high. Thus, a practical minimum for 20 meters is around 30 feet. You should consider a vertical if you can't get it that high. What you need depends on what you want to do. I'd suggest a minimum of 500 watts and 40 feet for casual voice operation. But, 100 watts would be plenty for CW or FT8 operation. 100 watts would also be plenty if you had a 70 or 100 ft tower, even during our current very low solar flux conditions. http://www.voacap.com/hf/ This site can be used to compare propagation with different antenna heights. http://www.karinya.net/g3txq/hexbeam/height_2/ This site attempts to predict how a Hexbeam will work at different heights. Keep in mind that 10M isn't expected to be good for another 5 years (my prediction) while 20M is the band that is open now during some part of the day. How much 20 is open depends on the low angle radiation of your antenna. An antenna that achieves very low angle radiation can take advantage of openings that "normal" stations miss. In time of high solar activity there are so many propagation paths open that all sorts of antennas can "work." Zak Lau W1VT ARRL Senior Lab Engineer |
| Feb 4th 2019, 14:58 | |
W4CWLTotal Topics: 0 Total Posts: 0 |
Thank you so much! Very helpful. How much interference to the horizontally polarized beam would my brick house be if the tower were, say 20 feet away from it? Too much to be worth it? |
| Feb 4th 2019, 15:17 | |
WA8NVWTotal Topics: 0 Total Posts: 0 |
If you use a wire antenna (non-rotatable) you can probably use a smaller vertical center support, such as a flagpole. All antennas are a compromise, it just may take you longer to work enough contacts for DXCC, WAS, Grid Squares, or whatever your goal may be. You just have to transmit your signal and be heard at the other end. |
| Feb 5th 2019, 09:53 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
A simple wire antenna could be used to evaluate interference issues. Radio frequency interference can degrade reception by many S-units. It may be worthwhile to find and fix RFI sources before making an substantial investment. Zak Lau W1VT ARRL Senior Lab Engineer |
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