[TowerTalk] low band receiving antennas options

[Tom Rauch]

Hi Rick,

> bands. Now if I did my math right this works out to about 301 ft which
> I understand is considered a short Beverage and short Beverages don't
> work well. Now I think I could get 2 of these short Beverages in

Cone of silence lengths have little advantage for receiving S/N over 
other lengths, unless you happen to have noise that is 
concentrated in the null area. Odds are you will never know the 
difference if you use those lengths or not.

Short Beverages are sometimes better than nothing, but to offer 
substantial performance improvements they MUST be terminated 
and they must be somewhat close to 1 wl long or longer 
**electrical*** length. The electrical length is ALWAYS longer than 
the physical length in wavelengths. At my QTH, the velocity factor 
of Beverages is about .9 or less, so a 500 foot Beverage looks 
500/.9 or 555 feet long or slightly longer electrically.   

You can see detailed discussion of how directivity influences 
receiving on my web page, www.w8ji.com

> behind the house running NE/SW and NW/SE If I made them bi-directional
> I would be covering most of the DX areas from my QTH ( TX).

I hope you mean reversible, and not bi-directional! You give up 
around 3 dB of S/N ratio with an unterminated beverage if noise is 
evenly distributed around the antenna on a shorter Beverage, and 
more if the noise comes from what would have been a null. In 
addition, they never receive as well off the feedpoint end even if you 
do not terminate them. Beverages tend to "self-terminate" because 
of losses in the antenna and earth below the antenna, so there is 
always some F/B even when unterminated. 

> Is this a bad idea? Would I be better putting up a K9AY loop?

K9AY loops function as two short phased verticals, except there is 
some additional response at high angles from the horizontal 
component of the sloped wires. Because two phased verticals 
aren't all that directive other than a deep null off the back, they (and 
other antennas like the K9AY loop) have limited signal-to-noise 
advantage. The exception is when unwanted signals or noise 
primarily comes from the null area. Of course if that is all the room 
someone has, any directivity is better than none!

Because of the limited directivity of a Flag, EWE, Pennant, or 
K9AY loop, even a modest length Beverage is generally much 
better. You can model it using the guidelines on my web page for 
determining receiving directivity factor if you have Eznec for 
Windows, or another program that calculates average gain.

> Since I own the land they will be on and it is not being used for
> anything I could leave these up year round. I haven't yet gone out
> there and measured the area yet but looking at the map that came with
> my deed it looks do able if I slant them across the property  but not
> actually having them cross each other. 

It does NOT hurt to have Beverages cross, as long as they are 
separated by a few feet near the crossing point. It does hurt to have 
the ends near each other.

By the way, there is no need to slope the ends downward as some 
suggest. Sloping the ends does nothing to reduce vertical pickup, if 
it did the K9AY loop and Flag antennas would not work! 

You also might use the Binocular cores I suggest on my Web 
page. It only takes SEVEN turns of wire to make a good 
transformer, not 20 or 30 like the wrong type of core requires. With 
the correct core the transformers work better and are much easier 
to wind. 
73, Tom W8JI
W8JI@contesting.com 

________________________________________________________________________
Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at http://store.eham.net.
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