If there is terrain above you, a 1/4 wave ground plane. If you are above everything, a 5/8 wave ground plane.
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Base Need base antenna advice
- Thread starter EricExtreme
- Start date
S&W357
$upporting Member KO4RJD....WDX-556
Its about take off angles. As an antenna gets to a half wavelength or longer then lobes and nulls start to form. Those lobes have gain, the nulls have losses and some of those can be as much as -30dB or more meaning the signal strength in those nulls is a thousandth of that where there are no nulls.
Take a look at the following image.
This shows the gain of the antenna at various take off angles from horizontal. Now for regular contacts and even DX you'll not notice a massive difference between the two, there's roughly only about 3dB difference at 0-10 degrees take off where DX is between the two, barely a S point. However where there is a MASSIVE difference is at around 30 degrees from horizontal where the quarter wave has a 15dB advantage over the 5/8 wave, several S points on a CB S meter. If you live in hilly terrain then the take off angles where the 5/8 wave has the null can be where you make contacts and this can be the difference between making a contact or not.
Now take a look at the situation for mobiles. Whilst it doesn't affect us on CB as there's no such thing as a 5/8 wave mobile antenna despite what claims are on the box, it does for those operating amateur VHF for example.
I have a friend who runs commercial repeaters on towers on high hills and found that when he was using 5/8 wave antennas on vehicles that operated closer than other customers they were having problems accessing the repeaters. Changing to 1/4 waves cured the problems. Fitting 1/4 waves to the customers who were more distant made no noticeable difference over the 5/8 waves.
Everyone gets hell bent on getting 1/2 waves, 5/8 waves etc but the simple fact is that they'll notice little if any benefits over a simple quarter wave.
S&W357
$upporting Member KO4RJD....WDX-556
https://www.worldwidedx.com/threads/a99-question.220046/page-2#post-601655
It isn't so much the lobes as the nulls. We've been over this before...
It isn't so much the lobes as the nulls. We've been over this before...
I think we read to much into TOA with different antennas.
Read here.
https://www.worldwidedx.com/threads/the-myth-surrounding-antenna-take-off-angles.140770/
Good info.
73
Jeff
Read here.
https://www.worldwidedx.com/threads/the-myth-surrounding-antenna-take-off-angles.140770/
Good info.
73
Jeff
This
And this
Unless the antennas are mounted essentially at earth level, you won't notice a difference between their radiation angles. I'm not saying that length doesn't have its effect, but in the so called "real world" it is essentially the third string when it comes to determining radiation angles, and that is being optimistic.
The DB
And this
Unless the antennas are mounted essentially at earth level, you won't notice a difference between their radiation angles. I'm not saying that length doesn't have its effect, but in the so called "real world" it is essentially the third string when it comes to determining radiation angles, and that is being optimistic.
The DB
A 1/4 wave ground plane has a higher angle of radiation than a 5/8 wave ground plane or 7/8 wave vertical. If you are in a valley, are amongst sprawling rolling hills, or you are surrounded by mountains that are higher than you, a 1/4 wave ground plane will provide a better chance of getting your signal over those mountains/obstructions. In a valley, the signal from the 5/8 and 7/8 waves are more likely to terminate at the obstruction. If you are above everything, the 5/8 wave ground plane or 7/8 wave vertical is what you want. Look at the radiation patterns of a 1/4 wave ground plane, a 5/8 wave ground plane, and a 7/8 wave vertical antenna. See the null at the 12:15 to 2:15 position on the 5/8 & 7/8 waves? That's the part of your signal that will get you over obstructions. People always think of gain first. Terrain is always my first concern. Here in Colorado, if I'm sitting up on a 14,000 foot mountain, a 5/8 or 7/8 wave will outperform a 1/4 wave. If I'm down in the valley, a 1/4 wave is more likely to work better. Cheers. Dean.
Mounting height is very important: https://www.qsl.net/df3lp/projects/vertical/index.html
Mike
Mike
I agree Mike.
The TOA can change drastically depending on the height of the antenna.
There are variables with antennas that can make it difficult to say that a
1/4 wave or 5/8 will act exactly like this at your station.
Different antennas at different locations with different results is why it is hard to say " this will work the best for you"
We can use our basic knowledge about antennas to pick a starting point but It often takes some trial and error to find what works best for you at your location.
Marconi ( old grampa) said it best .
We are just lucky that mother nature allows us to talk at all.
73
Jeff
The TOA can change drastically depending on the height of the antenna.
There are variables with antennas that can make it difficult to say that a
1/4 wave or 5/8 will act exactly like this at your station.
Different antennas at different locations with different results is why it is hard to say " this will work the best for you"
We can use our basic knowledge about antennas to pick a starting point but It often takes some trial and error to find what works best for you at your location.
Marconi ( old grampa) said it best .
We are just lucky that mother nature allows us to talk at all.
73
Jeff
S&W357
$upporting Member KO4RJD....WDX-556
Because my A99 antenna is vertical. The wire dipole could hang vertical if I wanted another vertical antenna...but I don't.
Sometimes flat side just works better...sometimes it doesn't.
Free gain of a couple of dB due to ground reflection but only of use when DXing due to cross polarisation with local contacts as they'll be pretty much using vertical antennas so that free couple of dB gain for DXing becomes a 20dB loss for local contacts due to cross polarisation.