10m twin lead j pole questions... Problems

[mr_fx]

OK so I tried building a 300 ohm twin lead j pole...

I followed the directions for 450 ohm window line seen here

http://www.qsl.net/dk7zb/J_Pole/wiremanjpole.htm

I used some random 300 ohm twin lead I had laying around (the black hard plastic stuff with windows through it) for the matching section,

and 18g solid insulated "underground" wire for the Top section...

I did I quick test... But I could only get the bottom of the antenna 1 foot off the ground (I'm lazy)

The results are as follows:

Impedance: 57
Reactance: 7
Swr: 1.1
Frequency: 25.430mhz
2.0 swr range: +/- 650k

My target frequency was 28.500mhz

So my question is is the fact that I have mounted the antenna so close to ground the problem? Has this detuned the antenna? It seems like that is an awful lot of Detuning

Or is it possible that I need to adjust the length of the main elements?

Or do I need to adjust the length of the matching element?

Or is everything just too long because of velocity factors?

Or do I need to adjust the feed point location any ideas?

 

[vkrules]

1/4 wave matching section will have to be adjusted for the Velocity factor of the cable you are using. If you cant find it . Sweep it with a analyzer or dip meter.Original article was using .905 .Your cable is obviously lower The 1 ft off the ground is most likely pulling it a little low as well.

 

[vkrules]

Vf of tv ribbon can be from .77 to,87 depending on type, that's a long way from the .905 used in the article..

 

[Grant Aldrich]

I thought j poles needed to be a minimum of 1/4 wave lenght off the ground to get good performance. ?