[Xastir] Portable Digipeater Antenna?

[Ray Wells]

Jason Winningham wrote:

>
> On Jul 1, 2007, at 4:23 PM, Ray Wells wrote:
>
>> Given that a J-pole is only a dipole with an alternative feed  method 
>> (i.e. at the end rather than the centre), I have to wonder  where 
>> this gain comes from.
>
>
>
> beats me, but when we fly 'em on the balloons, the J-pole has a  
> better range.  Could be that the lack of a balun isn't so bad with a  
> J-pole than with a dipole.  Could be some other construction issue, too.
>
> -Jason
> kg4wsv
>
>
>
Was it a very old (about 35 years ago) QST article that headlined "My 
Dipole Has A Gain Of 79dB"?

The crux of the article was that you need to know what you're comparing 
with. In the magazine article the comparison was with a dummy load!!

When you run them in a balloon, do you hang the J-pole down from the 
balloon?

The reason I ask is that a dipole has maximum radiation at right angle 
to the element. An end-fed dipole is no different, providing the pattern 
isn't being disturbed by "something". The J-pole, being an end-fed 
dipole "should" be the same.

Here's the "but". If the feed section of a J-pole radiates (and it often 
does), it radiates out of phase with the dipole element,  causing the 
radiation pattern to move away from being at right angles to the 
element. With an inverted J-pole, i.e. one hanging down from the ballon, 
the antenna pattern would have downward tilt, a desirable characteristic 
given the height a balloon can achieve.

This could be a case of having the antenna pattern where you want it 
rather than the absolute gain of the antenna, a case where your 
particular antenna does indeed work better than some others.

Ray vk2tv