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Vertical antenna for DX
On Jan 12, 6:20*am, "Peter" wrote:
I'm proposing to build a new multi-band HF antenna. Previously I used simple relatively low (8mtr) dipole (28mtr total length) feed with ladder line and matched with a Z-Match tuner. Worked ok, but was useless for DX. Shouldn't have been. Maybe not as good as a higher dipole, but you should have been able to work some DX. I once used a 40m dipole camping which was about 8 ft off the ground. I tried it on 15m, and was working JA's left and right. And 24 ft up is a good bit better than 8 ft. My proposed antenna is to be vertical (7mtr radiator) to be used on bands from 10mtr to 30mtr. I have heard that vertical antennas are more susceptible to noise! No. There is no difference as far as the antenna. It depends on the polarity of the noise source. If it's vertical, then yes, the vertical would pick up more noise. If the noise source was horizontal, which is often is these days, then the dipole would receive more noise. Many man made noise sources are vertical, but that's no different than having a desired signal being vertical. Noise is RF the same as any other signal, and follows the same rules. Being crossed polarized will generally give you about a 20 db loss in signal. That will apply the same no matter if it's a desired signal, or noise. This only applies to a local space wave, which is how most noise arrives . It gets a lot more complicated for sky wave, and usually means a good bit less difference overall. So don't worry about noise until it possibly becomes an issue. It's also quite possible for the increase in signals to be greater than the increase in noise when working long paths where the vertical has an advantage over the lower dipole. They work real well for DX and also local space wave coverage, which is fairly popular on 10m. But I recommend an elevated antenna when using the higher bands. I would not use a ground mount unless I had no other choice. The R5 mentioned is a good one for that application. I'm wondering how you will feed a 21 ft radiator for all bands using a home brew design. It's not as simple as it might seem for proper operation if elevated. The R5 is a "1/2 wave" type design that does not require radials. It's pretty convenient. But if you use a trapped 1/4 wave ground plane type of scheme for all bands, you will need at least one ground radial for band, and preferably at least two spaced 180 degrees apart. And that's just a minimum. Most ground planes I use have at least four radials. |
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