Antenna height

I read a lot on the net about antennas, their design and construction, and sometimes I see references to "optimum height for a (j-pole, dipole, etc). I read last night that optimum height for a half-wave dipole is one-half wavelength from the ground. Since I'm talking about scanner antennas here, as that is my hobby, is that really something to think about when erecting one of my new metal monstrosities? On this forum, and most others I've visited, the longstanding opinion is "Height is King-the more the better." Isn't it always better to try to get your antennas above the closest obstructions, as in the trees? Seems like I get better range on all my home-builts at the tallest placement, or is reception really just totally weather-dependent?

Apples and oranges. The article you read is most likely talking about horizontally polarized antennas and the ground acts as a reflector. Nearly all scanner antennas are vertically polarized and use no reflector, so the spacing would apply from the nearest horizontal element. Are you sure they said the same thing about a j-pole? those are usually vertically polarized and have virtually no reflection from the ground.

In general, you want the scanner antenna as high as possible. But, in RF dense areas that may not always be the optimal decision. In fact less antenna is more in some cases.

Antenna Height

" I read last night that optimum height for a half-wave dipole is one-half wavelength from the ground"

this is correct/important for the lower frequencies (below ~30MHz), all though it technically applies to all.

" is that really something to think about when erecting one of my new metal monstrosities? "

for the VHF/UHF/800 ranges, other factors become more important.

"Height is King-the more the better." Isn't it always better to try to get your antennas above the closest obstructions, as in the trees?

Yes. As frequency gets higher, the radio waves act more and more as straight beams (think light rays) that can be blocked by objects/terrain/other stuff. This is limited by coax line loss and practical mechanics (you can go too high in some instances.....)

Seems like I get better range on all my home-builts at the tallest placement, or is reception really just totally weather-dependent?

Actually, height, weather, other radio sources, even time of day can have an influence on radio waves.

Keep reading, there are reasons RF and antenna theory are sometimes refered to as magic/black arts....

doublescan: you should be able to get Jefferson Cty, and one county around Blount co with an antenna at 20 feet. Now if you are located in a hollow, with hills all around, you got troubles, As has ben stated , height is most important but on 800 mhz trunking, simulcast issues can develop where a lower antenna is better. Less is more in that case. VHF analog, height is very important but again, vhf and 800 more so, are line of sight, very little "bending" of radio waves, like what we experienced in cb low low bands.Some mounting location, that is clear of structures around your monitoring location, (clear the roof), clear of trees hopefully. N ow Blount cty appears to be analog, probably the bases are on a repeater , you should hear them but the mobiles, may at times be weak or unreadable. Not such as bad thing, as if you can't hear a mobile, they are a ways from your location. In trunking, mobiles and bases sound about the same. Nice to listen to, but the mobiles could be a block away and you don't know it.

antenna placement

Thanks for the replies-good points in all of them. I didn't really specify what I was talking about, did I ?
VHF airband is my main focus lately. And I AM in a hole with 1000' peaks in 3 directions, lol. Somehow though, I can usually hear the Bham RCAG and lots of planes in the air traffic. The local PDs and SO are all on repeater, so no problem with that. The weather affects my location a lot on airband, like was said-it's almost magic to receive well on some days. Finding the right location to beat the trees in just the right direction is a trick.
Guess I thought I wouldn't have to climb as much if the height factor wasn't as important, it's not nearly as much fun as when I was 30, lol. Must be getting lazy, lately I'd just as soon cut a tree as to try to reach over it!

Doublescan, I used to live in Boaz. And I used a back of set ant, I could hear Marshall Co and blunt Co, but I did live on sand Mt with good height. The ant was a center load and that too may have been a help, good luck. EDWin so calif

height

oldradioguy2010 said:

Doublescan, I used to live in Boaz. And I used a back of set ant, I could hear Marshall Co and blunt Co, but I did live on sand Mt with good height. The ant was a center load and that too may have been a help, good luck. EDWin so calif

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Yes Edwin Sand Mountain would probably be a good location for radio-there's a rcag somewhere that I can sometimes pick up on my handheld scanner (with the rubbie duck antenna, haha) when I'm driving near Boaz. Just for grins-the "FM FOOL" calculator says to get line of sight for most of the popular FM radio stations in my range, that I would need a tower between 500-850' tall. Now if I can just find a spare couple of hundred thousand I'd be rocking.