[Antennas] measuring SWR

2003年5月10日 15:08:02 -0500

I don't claim to be an expert I can only tell you what has worked for me in 
the past. I've always had the best results building jpoles when I treated 
the J as a transmission line and made the ratio of conductor diameter to 
spacing to be around 300 ohms.
Yes, in theory, the top of the J is infinite and the bottom is zero. In 
practice I find that either end comes up a bit short on either end. that's 
my experience.
I just thought I'd offer my experiences with building Jpoles in an attempt 
to help. After reading your response and 6 others off the list (one of 
which was quite abusive) I see now I shouldn't have bothered. Obviously 
your 30 years in amateur radio trumps my 25 years as a paid professional 
communications technician. I will now shut up and unsubscribe from this list.
At 03:31 PM 5/10/2003, Joe Mayenschein wrote:
>"Douglas J. Koehler" wrote:
>> > Mike,
> >
> > I've built around a dozen j-poles and variants in the past 10 years and
> > what you've got is an impedance mismatch. Your feedline is 50 ohm
> > unbalanced and your antenna is probably around 300 ohms unbalanced.
>>Now I also have built dozens of "J" Poles in my almost 30 years in this hobby,
>And the above statement is a bit confusing to me,
>>Yes the balanced to un-balanced thing is correct,, BUT,, I beg to differ 
>on the
>300 ohm statement,, IIRC the position of the taps determine the antennas
>impedance.
>>0 ohms at the base of the stub (connected to the short) and nearly 
>infinite at
>the end of the stub. or at least several thousand ohms,,
>>and everywhere in-between from 0 to the infinite. That's why they are soo 
>very
>easy to match..
>>Joe WB9SBD
>>>>- - -
>>Your moderator for this list is:
>Larry Wilson KE1HZ [email protected]
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