I believe the reason that verticals work better on lower bands is
a result of lower takeoff angles on the low bands, low frequencies,
whereas as you move to higher frequencies, the takeoff angle
seem to be higher also, Seoul that the radiation is not going in
the direction her place she wanted to go.
dipoles seem to radiate best at one half wavelength above Earth.
The higher frequencies have shorter dipoles, and shorter
wavelengths above Earth, so it is easier to put up a low, but
effective dipole on a high frequency band, but very hard to do
that on a low frequency band, because the half wave is so long.
In other words, a high-frequency dipole closed of the earth is fully
effective. A lower frequency dipole is not, for various reasons
including reflected waves off the earth, and lower takeoff angle and all
that jazz. So you use a vertical on the low bands because it has a more
suitable takeoff angle and radiation pattern on the low bands, but you
prefer the dipole on the higher bands because it has a better radiation
pattern than high frequencies have on the vertical.
Whew... I sure hope any of that made some sense.
Happy trails and 73. ---- Richards - K8JHR ----
=============================================
Richard (Rick) Karlquist wrote:
> Any explanation of verticals needs to address the demonstrated
> fact that they work very well on 160 meters, and still work well
> on 80 meters but gradually become ineffective as the frequency
> goes up. Either the ground or the ionosphere or both are frequency
> and/or polarization dependent.
>
> Most treatises on verticals completely punt on these issues.
>
> Rick N6RK
>
> Al Williams wrote:
>> ----- Original Message ----- > IN REALITY I THINK WE SHOULD BE TALKING ABOUT
>>> GROUND RESISTANCE...
>>
>> I have difficulty in accepting the explanation of poor vertical antenna
>> performance due to ground loss.It seems to be the culprit in about all
>> antenna books going way back in years but is never explained. My
>> understanding is that verticals do not get the benefit of ground reflection
>> that horizontals get; that the radiation of the wave may be partially
>> absorbed on its path away from the antenna but this occurs not within the
>> area that radials woul alleviate.
>>
>> This leaves the radials as providing a better return path for the return
>> currents. However, it is my understanding that antennas radiate because of
>> the changing (accelerating) current in them which means that the antenna is
>> charging and discharging, If this is the case then the charging and
>> discharging has to be offset with something that is of the opposite
>> polarity. That something in the case of the vertical is the ground if there
>> are no radials.
>>
>> When radials are added, the antenna itself can better charge and discharge
>> which is the real problem with the ground resistance
>> being only an inhibiter?
>>
>> Any corrections or explanations is welcome.
>>
>> k7puc
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|