Something for the Antenna gurus...

[magnuman]

I wish to make an antenna for the following frequencies on one boom using dipole elements and one feed line.
7.150mhz, 8.1 mhz, 10,1 mhz, 12.4mhz.
Would it be feasible to mount them in a line on a 6m boom and feed them together (not crossing over like a log periodic)
Could/would something like this work?
Appreciate the input.

 

[HomerBB]

multi-band yagi antennas are quite common. I have not built nor run any, as I am only a CBer, but several of my friends do.

here is an example of several Yagi antennas on one boom:

 

[RatsoW8]

I'm not really understanding what you are trying to do. Are you trying to make a milti-band dipole(fan or rotatable) or a directional antenna (yagi)? A two element yagi for those bands is going to require some engineering. A yagi is not a situation where you can just slap some elements on a 6 meter boom and expect it to work.

 

[Captain Kilowatt]

I'm not really understanding what you are trying to do. Are you trying to make a milti-band dipole(fan or rotatable) or a directional antenna (yagi)? A two element yagi for those bands is going to require some engineering. A yagi is not a situation where you can just slap some elements on a 6 meter boom and expect it to work.

Indeed. A dipole for 7.15 MHz is about 66 feet long which is no small task to construct and keep in the air. Even the shortened loaded driver element for 40m on my Explorer 14 is still 42 feet long.

The big issue I see is the frequencies desired are too close that the element will interact yet too far apart that a single element (or two) will not cover it such as 7.15 and 8.4 as well as any other two adjacent freq. bands the OP desires. Getting a single element to operate on CB and 10m or maybe even 10m and 12 is not that hard because the frequency difference is much smaller as a percentage. An LPDA (log periodic dipole array) is the way to go. A simple log cell can be made to cover the range 7.15-12.4 fairly easy but it will take all of that 6m boom and then some if you want any real gain or directivty.

 

[magnuman]

Indeed. A dipole for 7.15 MHz is about 66 feet long which is no small task to construct and keep in the air. Even the shortened loaded driver element for 40m on my Explorer 14 is still 42 feet long.

The big issue I see is the frequencies desired are too close that the element will interact yet too far apart that a single element (or two) will not cover it such as 7.15 and 8.4 as well as any other two adjacent freq. bands the OP desires. Getting a single element to operate on CB and 10m or maybe even 10m and 12 is not that hard because the frequency difference is much smaller as a percentage. An LPDA (log periodic dipole array) is the way to go. A simple log cell can be made to cover the range 7.15-12.4 fairly easy but it will take all of that 6m boom and then some if you want any real gain or directivty.

Was thinking of the log but it will be big...I might just try a couple of the dipoles on a small boom feed them together and see what happens. Looking at remote balanced tuners but they don't come cheap and results are mixed from what I can read.

 

[Captain Kilowatt]

Was thinking of the log but it will be big...I might just try a couple of the dipoles on a small boom feed them together and see what happens. Looking at remote balanced tuners but they don't come cheap and results are mixed from what I can read.

Anything for those bands will be big if you want full size or anything near it. As for a remote tuner, why a balanced tuner? Go with a regular tuner and use a balun on the output and feed the array with open wire or ladder line feeders. Until I can get my yagis up in the spring/summer I am using a Yaesu FC-40 auto tuner remote located outside the far end of the house from the shack. I have a 1:1 current balun on the output and feed a doublet with 450 ohm ladder line.

 

[mechanic]

Anything for those bands will be big if you want full size or anything near it. As for a remote tuner, why a balanced tuner? Go with a regular tuner and use a balun on the output and feed the array with open wire or ladder line feeders. Until I can get my yagis up in the spring/summer I am using a Yaesu FC-40 auto tuner remote located outside the far end of the house from the shack. I have a 1:1 current balun on the output and feed a doublet with 450 ohm ladder line.

Was thinking of the log but it will be big...I might just try a couple of the dipoles on a small boom feed them together and see what happens. Looking at remote balanced tuners but they don't come cheap and results are mixed from what I can read.

I use wire dipoles for any band 10 megahertz and lower (longer wavelength). Using aluminum dipoles at 40 or 75 meters are an engineering nightmare!

73 mechanic

 

[Captain Kilowatt]

I use wire dipoles for any band 10 megahertz and lower (longer wavelength). Using aluminum dipoles at 40 or 75 meters are an engineering nightmare!

73 mechanic

Agreed. There are a few commercially made rotatable dipoles for 40m but most are shortened. The QK-710 modification kit for tbe Hygain Explorer-14 will allow the drivet element to operate on either 30m or 40m. I set mine for 40m and it is 42 feet long and heavy enough to need a truss. Os course a lot of that weight comes from the extra large 20m traps and added capacity hat. For 80m I plan to use some quarter wave half slopers arranged around the tower and remotely switched.

 

[magnuman]

I think you are right. I like symmetry so will go with the 40m dipole sloping off the tower fed with 450 ohm ribbon @ 90 degrees and back to a balanced tuner in the tower.
Cheapest and easiest without hanging an more iron on to of the tower.
thanks,
Dave

 

[Heavy Metal]

Does a log periodic have to be horizontal or vertical or came it be like a V?, back in late 70's I was doodling up one for 10m 11m 12m (25-30mhz range), and down to 20m for fun. But agree Capt K. 40 and below wire is looking like best way to go, space saving thought of a cloths line type wire lol.

 

[Captain Kilowatt]

Does a log periodic have to be horizontal or vertical or came it be like a V?, back in late 70's I was doodling up one for 10m 11m 12m (25-30mhz range), and down to 20m for fun. But agree Capt K. 40 and below wire is looking like best way to go, space saving thought of a cloths line type wire lol.

Almost any antenna can be configured for vertical, horizontal, or as a VEE. Physical constraints will be the determining factor as to how you actually mount it. I cannot imaging a log periodic for 14-30 MHz being vertical however. The mast would have to be 35 feet long and then the antenna elements would extend 35 feet above and below the mounting point.

 

[Heavy Metal]

I was more so in a VEE rather than vertical, agree on the contrails of it as well. That a log periodic can be done that way or just horizontally. Think not only able to do both polarities it also shortens the width of it too vs being solely horizontal.

 

[Captain Kilowatt]

Shorter yes but both polarities no. Not really. A VEE tends to be horizontal with a very small vertical component off the ends.

 

[Heavy Metal]

Ah I see, so when all these people flip their + to x their not getting a true best of both worlds Huh. Just saving space to a point?

 

[Captain Kilowatt]

An X or a + sounds like a dual polarity yagi or a quad. A VEE is exactly that a V shape or an inverted V which is different than an X or a +.