[Elecraft] Antenna Separation for Diversity

[Tom W8JI]

I really don't think this is the best place for antenna topics, but I want 
to be clear about my comments.

In my case I measured a well-constructed dipole without significant feedline 
radiation. The vertical was a good clean vertical with a good ground. The 
spacing was 3000-feet.

The strongest coupling by far was with the dipole almost, but not quite, off 
the ends of the dipole. The deepest null was with the dipole directly 
broadside to the direction of the vertical.

This makes total sense when we look at the real polarization and pattern of 
a dipole. A dipole is only perfectly horizontal polarized directly 
broadside, and has increasing vertical tilt to polarization as we move off 
towards the ends.

The Carolina Windom, however, has an unpredictable polarization tilt to the 
pattern. It is NOT dual polarization or diversity, it is simply a dipole of 
sorts with significant feedline radiation, and as such will be unpredictable 
in polarization tilt with direction and elevation.

This all would be better on an antenna forum, so this is my last comment. 
:-)

73 Tom


--- Original Message ----- 
From: "Brett Howard" <brett at livecomputers.com>
To: "'Tom W8JI'" <w8ji at w8ji.com>; "'elecraft'" <elecraft at mailman.qth.net>
Sent: Thursday, June 24, 2010 9:20 AM
Subject: RE: [Elecraft] Antenna Separation for Diversity


> Huh... Broadside to the vertical provided minimum coupling?  Well I'm 
> going
> to be slapping things together tomorrow and trying them out and trying to
> take a bunch of measurements and logging it all.  Was just wondering if
> anyone else here had a similar setup and might have an answer here.  I'm
> figuring I'll probably be able to pull off about 150 to 200 feet between
> them... Lets hope its enough.  If not I can always make one of them RX 
> only
> and put the ICE Receiver Limiter box on it.
>
> ~Brett (N7MG)
>
> -----Original Message-----
> From: Tom W8JI [mailto:w8ji at w8ji.com]
> Sent: Thursday, June 24, 2010 6:00 AM
> To: Brett Howard; elecraft
> Subject: Re: [Elecraft] Antenna Separation for Diversity
>
> Brett,
>
> No one can answer that question for you, because both antennas are
> unpredictable in nearfield performance. Also the layout of the antenna and
> what is around, under, and between the antennas is very important.
>
> With such a large soup of unknowns, plus there might be other transmitters
> on site (?), the only way to really know is to try it.
>
> If you had a normal dipole and wanted interaction to a vertical of known
> efficiency I have all that data. One thing I learned is minimum coupling
> from a good dipole to a good vertical was with the dipole BROADSIDE to the
> vertical, not at right angles as I assumed without thinking.
>
> The problem is the Carolina Windom is nothing like a dipole and not nearly
> as predictable as a dipole for nearfield or close farfield coupling, and
> that goes on top of the other variables that are bad enough on their own.
>
> Maybe you should go to an antenna forum, like on eHam or QRZ, armed with 
> the
>
> information of the safe signal level the K3 will tolerate. Other than the
> safe signal level, this is really an antenna theory question and a good
> answer would be too complex for a radio reflector.
>
> 73 Tom
>
> - Original Message ----- 
> From: "Brett Howard" <brett at livecomputers.com>
> To: "elecraft" <elecraft at mailman.qth.net>
> Sent: Thursday, June 24, 2010 5:14 AM
> Subject: [Elecraft] Antenna Separation for Diversity
>
>
>> So I know I'm going to shoot for as wide as I can get things... But for
>> two main antennas on a k3 one being a Carolina Windom and the other
>> being a 43 foot vertical.
>>
>> How much separation would one expect to be needed in order to prevent
>> the COR's from switching during TX @ 100Watts?
>>
>> ~Brett (N7MG)
>>
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