Dave Oldridge wrote:

Allodoxaphobia wrote in
:



On Mon, 02 Jan 2006 14:33:18 GMT, Dave Oldridge wrote:


Chris W wrote in
news:IT3tf.45644$ih5.19066@dukeread11:



I want to put a short 2 meter yagi and a long 70cm yagi on the same
vertical mast. The 70cm will be a horizontally polarized, center
mounted 17' boom and the 2 meter will be a vertically polarized, end
mounted 6 foot boom. How far apart do they need to be? I will only
be transmitting with one at a time but one could be receiving and
the other transmitting, the 70cm will be for ATV receive only for
now.


A good rule of thumb is to separate them by at least a half-wave at
the lowest frequency. In this case that means about a meter (39")
apart.


Not when they are orthogonally polarized. They can be 0.000
wavelengths apart. I.e., in the OP's case, the 2M elements can be
_mounted_ on the 70cm's boom.



You're right. I didn't catch the polarization thing. In fact, building
them on the same boom would be quite workable.



What if they are 2 different antennas and you can't put them on the same
boom, how close can I put them?

--
Chris W
KE5GIX

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On Tue, 03 Jan 2006 13:01:32 -0600, Chris W wrote:
Dave Oldridge wrote:
Allodoxaphobia wrote:
On Mon, 02 Jan 2006 14:33:18 GMT, Dave Oldridge wrote:
Chris W wrote:

I want to put a short 2 meter yagi and a long 70cm yagi on the same
vertical mast. The 70cm will be a horizontally polarized, center
mounted 17' boom and the 2 meter will be a vertically polarized, end
mounted 6 foot boom. How far apart do they need to be? I will only
be transmitting with one at a time but one could be receiving and
the other transmitting, the 70cm will be for ATV receive only for
now.

A good rule of thumb is to separate them by at least a half-wave at
the lowest frequency. In this case that means about a meter (39")
apart.

Not when they are orthogonally polarized. They can be 0.000
wavelengths apart. I.e., in the OP's case, the 2M elements can be
_mounted_ on the 70cm's boom.

You're right. I didn't catch the polarization thing. In fact, building
them on the same boom would be quite workable.

What if they are 2 different antennas and you can't put them on the same
boom, how close can I put them?

OK, if we're still talking about one vertically polarized and one
horizontally polarized, I'd slap'em together so that the vertical
elements are at least 1/4 wavelength from the horizontal's boom.

Or, you could do what some fellers seem to do: Spend all your time in
rraa, anguishing and arguing about antenna installation choices. After
all, which propagates best: The antenna on the floor of the garage, or the
one up in the air? HI!HI!

JONESY'S AXIOM:
You never put an antenna up just once.

Good Luck and Happy New Year!
73
Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
Pueblo, Colorado | @ | Jonesy | OS/2 __
38.24N 104.55W | config.com | DM78rf | SK