10 meter dipole mounted vertical

[airplane1]

I am thinking of putting a wire dipole up running it from top of tower to bottom with and offset of about 2-3ft. Is this a good idea or will it be better as an inverted v?

thanks.

 

[Robb]

http://www.worldwidedx.com/cb-antennas/31857-dipole-your-citizens-band-radio-base-station.html

This thread covers a LOT of related questions.

 

[Captain Kilowatt]

I am thinking of putting a wire dipole up running it from top of tower to bottom with and offset of about 2-3ft. Is this a good idea or will it be better as an inverted v?

thanks.

Inverted VEE. Too much interaction with it being parallel to the tower that close.

 

[Beetle]

You'll want to route your coax straight away from the antenna. That's not hard when you're installing a conventional dipole, but rather harder when you hang the dipole from one end (and worse when you're hanging it parallel to a metal tower! OWCH!)

 

[Shockwave]

When a vertical dipole must be side mounted to a tower we should understand the effects the tower has and use them to the best advantage. Mounting the antenna 2 or 3 feet from the tower will be too close for good results. It will block much signal on the back side of the tower and shift the antenna impedance.

Now if you space out from the tower closer to 1/4 wave or about 4 feet on 10 meters the effects are not so undesirable. The tower becomes a primitive reflector. You can face the antenna on the side of the tower you want to have the most coverage. You'll get about 2 db gain on that side and the rejection off the back won't be nearly as bad as if it were 2 feet from the tower.

The Sirio dipole is an excellent candidate for tower side mounting and is supplied with a gamma match and suitable side mount. Broadcast stations on FM have been side mounting dipoles at about 1/4 wavelength standoff for half a century and claim nearly omni directional patterns.

Since the inverted V or the dipole is suitable for use here, the choice should be determined by who you intend to communicate with? The inverted V gives a good split between horizontal and vertical but is more directional then the vertical dipole. Vertical is best for line of sight propagation to mobiles while horizontal at about 1 wavelength high is great for skywave DX.

 

[hookedon6]

consider putting it up as a sloper

 

[airplane1]

Thanks for all the great info given to me here. I have way enough now for what I was planning to do.

73, AP

 

[Captain Kilowatt]

Now if you space out from the tower closer to 1/4 wave or about 4 feet on 10 meters the effects are not so undesirable. The tower becomes a primitive reflector. You can face the antenna on the side of the tower you want to have the most coverage. You'll get about 2 db gain on that side and the rejection off the back won't be nearly as bad as if it were 2 feet from the tower.

The Sirio dipole is an excellent candidate for tower side mounting and is supplied with a gamma match and suitable side mount. Broadcast stations on FM have been side mounting dipoles at about 1/4 wavelength standoff for half a century and claim nearly omni directional patterns.

Just a little note of correction, 1/4 wavelength on 10m is about 8 feet, not 4 feet. Also broadcast FM stations have a more omnidirectional pattern due to a few other factors as well such as better penetration of the tower lattice structure itself due to smaller wavelength and also the fact that most FM stations broadcast either horizontal or a combination of vertical and horizontal polarity which helps to reduce the influence of the tower.

 

[Shockwave]

I don't know what I was thinking there. I meant to say 1/8 wavelength or 4 feet spacing works well on 10 meters. Going more then this will reduce any tower effects further. Going less then 1/8 wavelength and the antenna would have noticeable less performance and possible impedance issues.

With FM stations the tower standoff is often 1/2 wavelength because it's physically easy at VHF to get this much separation. The circular polarization FM stations use is not a mix of vertical and horizontal, it is a signal that rotates with each cycle of RF so that it's in all planes. With circular polarization on FM the tower lattice or cross sections can be the most unpredictable part of the anticipated radiation pattern. On commercial towers the cross sections are wide enough to be resonant at certain heights on the tower.

Lower bays may have cross sections of tower behind them that appear as reflectors and upper bays on the tapered tower may see directors on the tower behind them. I only used the FM dipole example because it's a known issue where there are some directional effects but the FCC still classifies it at omni directional. Yet they always pay the high riggers to set the bays on the side of the tower facing the market needing the most penetration.