| Home |
| Search |
| Today's Posts |
|
#14
January 20th 15, 09:12 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
Antenna recommendation needed
On Tuesday, January 20, 2015 at 12:31:04 PM UTC-6, wrote:
wrote: snip A vertical generally needs radials unless it's a "1/2 wave" type design. And even good verticals can be quite lackluster for close in work compared to a low dipole on 40m. Good at night to DX though. But like I say, he's gotta decide what he wants to concentrate on, and go from there. You are all over the place here and mixing apples and oranges. Yes, because you are dealing with apples and oranges in the real world, and until he comes back and describes what mode of operation he prefers most of the time, I include both options. A vertical has a low elevation angle. And not much at the higher angles. Which will make it fairly poor compared to a low dipole when used for general 40m NVIS use, say in the daytime. Any antenna that has a low elevation angle is "better" for distant communications than an antenna with a very high elevation angles. Sure, but until he comes back and describes his usual mode of operation, I'm not sure if that is what he wants at all times. A horizontal antenna less than a half wavelength in height has a vey high elevation angle. At .3 lambda it is 48 degrees, at .25 lambda it is 62 degrees, and at .2 lambda it is 90 degrees, i.e. straight up. I've modeled and used antennas for many years.. I know the usual patterns of the various options. This is called an NVIS antenna which is "better" for local communications out to about 500 miles or so on the lower bands. NVIS communcations is nearly nil much above 8 MHz at other than sunspot peaks. We are currently past the peak of the current sunspot cycle and heading for a minimum. The angles used for 20m stateside can be fairly high. I know from experience that a 20m dipole at 20 ft will work quite well for average distances. It will be quite good within 1500 miles, and still quite usable at DX distances. It will generally be a good performing antenna for overall use. And if the band condx are heading down as you say, he would more likely be on 40 and 20, than the higher bands. Will he work 40m in the daytime? If so, he will want to be on the low dipole, rather than the vertical. Would be like comparing fresh cut oranges to rotten apples. :/ A vertical antenna does not "need" radials, but it's performance is improved by radials. Sure. But if he's over med to poor ground, the losses can be substantial. I'm over quite good ground being on the Gulf Coast, and I had a full size 32 ft tall 40m vertical ground mounted with 32 radials. It was OK, but no real DX buster. At all.. I then raised the antenna to 36 ft at the base, and used 4 sloping radials as a ground plane. That antenna absolutely smoked the ground mount antenna to DX. So the ground radials obviously were a factor, and I'm over pretty good ground. A vertical antenna over average ground has a main lobe at about 30 degees and a gain of about 1 dBi. And? A vertical antenna over perfect ground has a main lobe at 0 degrees and a gain of about 5 dBi. I don't know anyone who lives on perfect ground. :| In a typical urban setting where there is landscaping and irrigation, the ground is most likely average to very good unless you are in the middle of a desert, which means even without radials the vertical's gain is going to be a few dBi. Adding a few radials will improve the gain and lower the main lobe but are not absolutely necessary. That is true for the area I live on, and obviously the number of radials made quite a difference in my case. Raising the antenna let me use less radials to equal a certain number on the ground. I was using 32 on the ground for only so-so DX performance. The four I used at 36 ft were equal to about 60 or so on the ground at that height in wavelength on 40m. Most verticals will get put in the middle of a lawn and it is trivial to take a lawn edger or weed wacker and cut a groove in the grass down to the dirt and staple down some radials. In such a setting you do NOT need the 120 radials of a commercial broadcast station with it's antenna in a barren field. I'd want a decent number to really brown the food. And you have to consider the price of wire these days. Copper wire can add up to $$$$. If he has trees to tie dipole legs to, he really only needs one support for the apex. The bottom line is a horizontal antenna needs three supports. Not if you use two supports for the whole antenna, and let the feed line drop from the center down to the ground and then to the shack. He doesn't actually have to let it drop to the ground, but in the case of coax fed, I prefer that in case of a lightning strike. And snubbing the shield to a ground stake at that point, even better. I like metal masts as an apex support, as it will usually take the strike and route it to ground, instead of the antenna, as long as the mast extends slightly over the feed point of the antenna. snip And the tuner/ladder line fed dipoles is another option if one wants all bands with one antenna. As is a vertical piece of aluminum tubing of whatever height you can put up with an ATU at the base of it. Sure, I never said it wasn't. Almost a gazillion options in the wide wide world of antennas.  But until he comes back and describes his usual mode of operation, I feel it's best to include all options, and not just limit it to verticals. |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| Weather Radio Recommendation needed | Moderated | |||
| looking for antenna recommendation | Antenna | |||
|
< |
Equipment | |||
|
< |
Equipment | |||
|
< |
Equipment | |||
Threaded Mode
