Random question

[jaythescanman]

I recently took two K40 4ft fiberglass whips and built a dipole out of a [ bracket center fed obviously. I have gotten phenominal results mounted horizontally on cb/11m 1.1:1 swr all
Around. my question is, if a guy was to build a second identical setup could he cophase them, mount one
Vertical and one horizontal?

 

[prcguy]

You could certainly do that but they would not be considered co-phased. Your power would be split equally to each antenna resulting in half your signal being lost to someone receiving you in vertical polarization and the same for someone receiving you horizontal. The other station would need a similar setup to recover both polarities simultaneously and after all that you would end up with the same signal strength (at best) as just using a single antenna.

For there to be beneficial gain the antennas would need to be the same polarization and spaced about 18ft apart for CB and you would get a little gain in a figure 8 pattern in line with both antennas and a null at right angles between them.

You could also space them about 9ft apart and feed them with an asymmetrical phasing harness of the correct lengths and make a two element beam that could be switched in two directions.

Since your starting with a short loaded antenna that has compromised performance, all of the above suggestions would probably radiate less signal than a single good full size 1/2 or 5/8 wavelength antenna.
prcguy

 

[LtDoc]

If the idea is to change polarization, simply rotating the thing 90 degrees would be a simple answer. That rotating can be done electrically (rotor) or manually (rope). There are 'problems' with either solution naturally.
If the idea is to achieve gain then phasing two or more of those antennas is certainly one way of getting it. There are 'problems' with that too.
So, pick the 'flavor' of 'problems' that you thing you can live with the easiest and have at it.
- 'Doc

 

[jaythescanman]

What im effectively wanting to do is minimize fade on DX/skip signals when they switch around in the atmosphere, so simply rotating the antenna wont work in this case. I see "big hair antennas" has one thats a 1/2 wave hor/vert dipole, was thinking along the same lines with the two k40. My main problem is, I cannot run a full 18ft base antenna do to the 'neighborhood counsel' as it is I had to fight with them to put the smaller horizontal up in the tree even though you cant see it.

 

[prcguy]

Since skip signals are randomly polarized you might get a slight improvement from a dual pol antenna but what really works is space diversity. You want a second antenna many (more than many) wavelengths away and preferably into a second receiver that is phase locked to the main receivers local oscillator. This is expensive and complicated but that's how it's done.

For AM reception you can also use a receiver with synchronous AM detection which really cuts down the annoying fade problem. Using SSB to receive AM mode also helps.
prcguy

What im effectively wanting to do is minimize fade on DX/skip signals when they switch around in the atmosphere, so simply rotating the antenna wont work in this case. I see "big hair antennas" has one thats a 1/2 wave hor/vert dipole, was thinking along the same lines with the two k40. My main problem is, I cannot run a full 18ft base antenna do to the 'neighborhood counsel' as it is I had to fight with them to put the smaller horizontal up in the tree even though you cant see it.

 

[nanZor]

What im effectively wanting to do is minimize fade on DX/skip signals when they switch around in the atmosphere, so simply rotating the antenna wont work in this case.

Correct - but you have no say in the matter at HF once reflected from the ionosphere. Once launched and reflected (line of sight is a different story), the actual polarity is never perfectly horizontal or vertical on the receiving end. You can design antennas to look in a certain direction however.

For example, if you were to create a "1 radial vertical" out of your pair of 4-foot antennas, the elevation pattern would look like this, so point the sole radial in the direction of interest. The best way to describe it is that it attenuates the back-end signal rather than providing any gain in the wanted direction.

 

[prcguy]

A 1 radial vertical is essentially a 90deg inverted V dipole on its side and will have both vertical and horizontal polarization off the broad side. Its fairly polarization insensitive but the drawback is its got about 3dB loss talking to a another station in pure vertical or horizontal pol.

Another problem is when done at HF the horizontal radial is usually on the ground or very close which incurs extra bonus ground loss.
prcguy

Correct - but you have no say in the matter at HF once reflected from the ionosphere. Once launched and reflected (line of sight is a different story), the actual polarity is never perfectly horizontal or vertical on the receiving end. You can design antennas to look in a certain direction however.

For example, if you were to create a "1 radial vertical" out of your pair of 4-foot antennas, the elevation pattern would look like this, so point the sole radial in the direction of interest. The best way to describe it is that it attenuates the back-end signal rather than providing any gain in the wanted direction.

 

[nanZor]

What makes it interesting for some, (or just out of necessity for lack of space), is the high elevation angle and directivity which may compensate for the 3db loss. That is, if you want a high elevation angle with a vertical - usually not, but for some purposes maybe.

Shorten the vertical element a wee bit, and put a capacity hat or t-wire loading on it. I think you and I are the only ones who dig what capacity hats do! That will help a little bit.

 

[LtDoc]

Simply rotating the antenna, horizontal to vertical or visa-versa(sp), WILL work. It's not fool proof, and keeping up with the changes in the received signal isn't easy, but it does work. Having one antenna in each polarization is an easier way of going about it. Switch back and forth to get the strongest signal. If you think about it, an automated system to do that is doing exactly the same thing.
- 'Doc

 

[prcguy]

If the intent is to minimize fading of skip signals then rotating from horizontal to vertical is usually not very effective because the fading is caused by multipath and signal cancellation at the receive location.

In this case going from H to V pol has very little effect, using SSB or AM Synchronous Detection on receive helps but the only sure way to mitigate the problem is with diverse antennas separated many wavelengths apart.
prcguy

Simply rotating the antenna, horizontal to vertical or visa-versa(sp), WILL work. It's not fool proof, and keeping up with the changes in the received signal isn't easy, but it does work. Having one antenna in each polarization is an easier way of going about it. Switch back and forth to get the strongest signal. If you think about it, an automated system to do that is doing exactly the same thing.
- 'Doc

 

[LtDoc]

And like I said, it isn't fool proof, or a sure thing. But it is more common, generally used, *less expensive* for the average listener (at least one with my budget).
- 'Doc