1/4 wave yagi

[solderjerk]

Anyone know of a good design for a 1/4 wave yagi (beam) for 10 meters? I've looked but can't seem to find anything. :?:

 

[W5LZ]

A 1/4 wave yagi? Really, or is it a 'loaded' yagi?
- 'Doc

 

[Beetle]

A "Yagi", by definition, has a driven element 1/2 wavelength long (electrically, not necessarily physically), a reflector about 5% longer and one or more directors, about 5% shorter. Unless you're heavily loading shorter elements, you won't get a 1/4 wave yagi.

 

[74IN]

I guess you could use a 1/4 wave end fed driven element and just stack all the elements on top of the boom.

Better off with a 1/2 wave.

 

[solderjerk]

Yeah I was wondering if there was such a thing or not. I was trying to cut down on space. Back to the 1/2 wave. Thanks.

 

[KD7UGY]

Most will tell you that it's impossible to use a 1/4 wave driven element and some type of reflector and get gain like a Yagi does but I'll tell you it is possible, how do you think all these keydown vehicles work? Although they are using a groundplane which I guess makes up for the other half of the missing dipole.

 

[Master Chief]

:idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea:

The light just came on! Thanks!

 

[W5LZ]

'UGY',
I don't think anyone was saying an antenna of a 1/4 wave length isn't possible, in whatever 'shape' it assumes. But, there are factors with the 'mobile beams' people use that mean that they can't be used 'fixed' without altering them into a more 'normal' type directional antenna.
You are correct in saying that the vehicle "makes up for the other half of the missing dipole", but there's more to it than ~just~ the vehicle. What's under the vehicle (the 'dirt') is also part of that 'missing half' of a dipole. The lower the band, the more the 'dirt' takes part in that balancing act.
The problem comes in with a 'fixed antenna because they are typically much higher off the ground than a mobile antenna. That height means that 'dirt' has much less play in that balancing act, some, but not nearly as much. (Unless you can manage to hoist that '48 Hudson car body to the top of your support pole/tower [Please take pictures!] not to mention rotating it!).
It is possible to reduce the overall area a yagi type antenna will occupy. That reduction in area also means there will be some reduction in the realized signal gain, and ease of making the thingy work to start with. It amounts to a reduction in element length of a couple of feet, sort of. Won't turn a large antenna (HF) into a very small one (UHF), but certainly will be smaller than usual (which we later found out was the aim of the whole thing).
It sort of boils down to "what's the point" in the end. If it provides a definite benefit, sure, why not. If it doesn't, what's the point?
- 'Doc

(That reduced size yagi will be unusual enough that 'they' will know somethings going on, right?)