co phase base ant

[357-magnum]

im thinking of runing two m400 stardusters 35 feet cophased parralleled west to east plus im on a hill over looking san diego any body have any experience with that

['Doc]

The idea isn't 'new' or unusual, it's been done before. The biggies are that the two antennas should be tuned identically, or as close as possible to each other (resonant and input impedances the same), and the phasing harness should be 75 ohms (or higher if you can find any). If you insert a switched electrical 1/4 wave section in one of those phasing lines you can 'swing' the direction of radiation 90 degrees, got it all covered, sort of. There are 'catches' to it, naturally, it isn't 'dirt' easy. But it's certainly possible.
Have fun.
- 'Doc

[RCIV]

Why 35 feet? With perfect phasing/matching, the pattern at 1 wavelength is for very sharp and narrow 16 degree lobes broadside (N/S in this case) and 60 degree lobes broadside (E/W) with very deep nulls everywhere else. Throwing in 180 degree delay would give you just about the opposite-- lobes where nulls were, and vice-versa.

Not that it's a bad idea, you just don't usually see 1 wavelength spacing in two element phased arrays. Just curious why you want that.


Rick

[RCIV]

I meant 60 degree lobes -endfire-. Don't see an EDIT button here anywhere, sorry.

[357-magnum]

im thinking of runing two m400 stardusters 35 feet cophased parralleled west to east plus im on a hill over looking san diego any body have any experience with that

*35feet high i meant and spacing about 10 feet ps thanks for the comments =]

[RCIV]

Ah, OK! There's nothing wrong with 1 wave spacing, by the way, I just wondered what you were up to!

Well, 1/4 wave spacing isn't going to do a lot for you driven in phase. I've had phased ground planes on 20 meters a couple of times spaced 1/4 wave and had them set up for in phase/+90/-90 degree phasing. I almost never used the in-phase setting (not seeing much difference between that and a single ground plane) and when I built the second array like that a couple of years later I didn't even have that as a option, wasn't really worth it-- and leaving it out simplified the switching.

What are you after with this one-- a bidirectional fixed pattern, a switchable bi-directional, fixed or reversible uni-directional pattern? Any of these are possible, but the spacing and phasing will depend on what you want to do, as Doc mentioned.


Rick

['Doc]

Try changing that phasing by 90 degrees, not 180 degrees. Big difference.
- 'Doc

[357-magnum]

got my second starduster today

[chrisbama351]

Try changing that phasing by 90 degrees, not 180 degrees. Big difference.
- 'Doc

Is 180 degrees out of phase 12ft and 90 degrees 6ft?
Thanks, ala"Bama" 351 in Colorado

[JAFO]

Try changing that phasing by 90 degrees, not 180 degrees. Big difference.
- 'Doc

Is 180 degrees out of phase 12ft and 90 degrees 6ft?
Thanks, ala"Bama" 351 in Colorado

Yes - when using 66% coax, like RG-213

50Ω identical lengths - 6' on ONE, then both each barrel connect to a 1/4 wave piece of 75Ω multiplied by the velocity factor, so if standard 81% RG-11 - then 87.5" for 27.185MHz
to a T connector then 50Ω to the radio.