> This for instance
> http://www.aytechnologies.com/TechData/ShortBev.htm
There isn 't enough detail in the description to understand the model and
the plots fully.
A 560 foot long "beverage" on 175 kHz has about 15 dB null off the sides at
5 degrees wave angle, and a few dB F/B at low angles.
The mode is the same as the K9AY, flag, EWE, and many other antennas use. It
acts like two short top-loaded verticals phased, and fires opposite normal
direction.
You can find bad places as frequency is varied, at different angles and
directions, but it is pretty tough to find a spot where any antenna has no
nulls at all.
> >It isn't in "Beverage mode", but it is in a mode that offers
>> directivity.
>>
>> They work that way, too.
>
> And what mode is that? Yes they work suprisingly well at LF, so well in
> fact that I can seperate stations on the same frequency, NDB's or the LF
> BCB.
No doubt. It models to be able to do that with 15 mS/m earth, or 1 mS/m
earth. Mine act that way too, and they acted that way every place I ever
lived.
>> Certainly they are not good antennas in comparison to something full
>> size,
>> and are not acting as a Beverage, but they do have pronounced directivity
>> at
>> lower wave angles.
>
>
> At LF its not much different than a BOG on 160 and its obvious that no
> pattern reversal takes place.
> Prior to these antennas the 175' Slinky also had good directivity on LF.
>
> Ive seen no models that explain this.
Everything is explainable. Nothing is magic, and very little (much to all of
our regrets) is a special gift, except being out away from noise, or moving
close to where we want to communicate.
> Thats always been my starting point, try it, then understand why, and then
> improve it.
It's all about phase shift and current. Nothing is magic.
For example, we sometimes feel good because an antenna has noticeable F/B
over 10 octaves. That really tells different people different things. It
tells me the phasing is far from optimum directivity phase at the high end
of the pattern frequency range. If I wanted the best 160 and 80 meter
antenna, I would intentionally forego a significant back null on 400 meters.
If I wanted a wideband null to never hear a certain direction more than raw
S/N ratio on 160 and 80, I'd use that delay.
It really all depends on what our goal is.
73 Tom
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|