Topband: Power Coupling in the USA

[Steve Ireland]

At 12:07 PM 5/05/2002 +0100, you wrote:
W4ZV said:
>Hi Steve!
>
>        I don't want to get into an anecdote contest with anyone
>but would just like to factually correct something you wrote.  I'll
>summarize my opinion by simply saying:
>
>1.  Vertical antennas are better DX antennas than low dipoles.
>2.  Any dipole less than 250' high is low (<0.5 wavelength).
>3.  Any 160 antenna (dipoles included) is better than no 160 antenna!
>
>                                                73,  Bill  W4ZV

VK6VZ replied:

G'day Bill,

I agree with you on the second and third points, but I guess my version of
the first - on 160m - would be:

1. Vertical antennas are usually better DX antennas than
(higher-the-better) dipoles at high latitudes (over 35 degrees), especially
over good conductive ground. Dipoles (the higher-the-better) are usually
better DX antennas than verticals at low latitudes (under 35 degrees),
especially over poor conductive ground.

This is not simply anecdotal, but is based on the physics of geomagnetic
latititude, power coupling, rather than just my own observation. 

I'd also add a fourth and fifth point.

4.  Wherever if you live, if you can, either have an antenna that has
substantial vertical and horizontal polarisation (such as an half-up
half-out inverted-L), can be switched from one to the other, or have two
antennas, one for each polarisation  - and make sure you switch regularly
between them. 

5.  Wherever you live, always try both polarisations.  The laws of physics
don't change, but the propagation of signals on 160m is a very strange
business and what works for you is what works. 


>
>VK6VZ wrote:
>
>>The other thing to note is that those DXexpeditions who equip themselves
>>with the great Battle Creek Special - an inverted-L antenna - get as much
>>radiation above 45 degrees as they get below it.  The BCS gets a lot of
>>credit as a low angle radiator, but it is also a good high angle antenna on
>>160m, with appreciable horizontal polarised radiation.
>

W4ZV wrote:

        This is incorrect.  You are probably thinking about a 3/8 wl 
>inverted-L which is indeed a high angle antenna.  The BCS is a loaded 
>50' high 1/4 wl inverted-L with approximately 70' horizontal.  Over good
>ground, EZNEC shows the 3 dB power points at 8 and 56 degrees with the 
>maximum at 25 degrees.  Over very good ground, it the 3 dB points are 4 
>and 52 degrees with the peak at 19 degrees.  I'm not taking the time to
>model the on-ground radials it actually uses but I would estimate its  
>performance lies between the two results given.  BTW, W8JI and I also
>have poor ground conductivities (2-4 mS/m) and the same was true for
>my location in Colorado.  Fortuntely a good radial system can overcome
>any ground conductivity for near-fields.

VK6VZ replied:

You are right in saying that my statement that the  BCS has as much
radiation above 45 degree as below it is incorrect - at 60 degrees it is
about 3dB down from maximum radiation and at 90 degrees it is about 7dB
down from maximum.

However, I stand by my statement that the BCS is also a good high angle
antenna, with appreciable horizontal polarised radiation.  On 160m, the
horizontal polarised radiation from the horizontal part of the BCS (in its
inverted-L configuration) fills in the pattern quite nicely at higher
angles, giving 16dB-plus more radiation straight up than a quarter wave
vertical antenna.   You could even say the BCS has 16dB gain over a
standard quarter wave vertical when it comes to straight-up radiation. 

Vy 73,

Steve, VK6VZ