[TowerTalk] Greyline Performance antennas

[Kim Elmore]

On 10/17/2020 1:23 PM, Jim Brown wrote:
> On 10/17/2020 9:38 AM, Kim Elmore wrote:
>> I have a F12 Sigma 80 antenna, which is an OCF vertical dipole with 
>> inductive loading at the feed point and a hairpin match. While it 
>> *requires* a common-mode choke at the feed point, it works very well 
>> for DX. On stateside contacts, I think its radiation angle is too low 
>> and performance for anything within about 400 mi is much worse than 
>> for my inverted V with (apex at 40 ft). On DX, though, it does MUCH 
>> better than the inverted V.
>
> Verticals shorter than about 3/4 wavelength, by their nature, have a 
> low radiation angle. It has nothing to do with the design of the F12 
> antenna other than it's height. This is made clear by a study of the 
> link I posted for my study of vertical antennas and horizontal 
> antennas, and by study of the ARRL Antenna Book, the ON4UN book, and 
> the Antennas chapter of the ARRL Handbook.
>
>  I have no radials beneath this antenna.
>
> By it's design, no radials are needed.
Nope; but I added that to remove all doubt.
>
>> I know a friend is buying a Greyline antenna for his QTH. They 
>> initially look a bit pricey, but I've not actually seen one, so I 
>> don't what the build quality is truly like. Assuming it's build 
>> quality is pretty good, and assuming it has a good CM choke, 
>
> From what I see on their website, that may not be a good assumption.

Maybe I should have said "... making sure it has a good CM choke," 
especially since you've taught us how to make them! Even if the feed is 
in the center (it could be if the transmission line is run up the bottom 
half) it still won't be balanced. A CM choke is always needed. I've 
become convinced that balanced antennas make analysis much easier (even 
possible) but that in the real world, there aren't any.  I have no idea 
what the electrical length is for 6 m or even 10 m, so the low 
radiation-angle assumption might be invalid on those bands.

Kim N5OP

>
> there's no reason why it shouldn't
>> perform relatively well given the constraints. Certainly better than 
>> no antenna at all!
>
> This last sentence is the key -- if you're stuck in an HOA, it's 
> better than nothing.
>
> 73, Jim K9YC
-- 

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)

/"A great second violinist plays second fiddle to no one." //– Robert C. 
Marsh, Chicago Sun-Times./