MFJ Dipole whip problem

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MFJ 1640t antenna. Portable whip antenna for 40 M that I was using as a base antenna with some results but not great. I thought I would improve on it by making it a dipole. I bought a duplicate antenna from MFJ and also their dipole mount made for this purpose, it is a MFJ 347. I hooked everything up per the instructions using a LMR240 coax cable 25ft long bought from the Ham Radio Outlet. The dipole is mounted about 15ft up on a non metallic pole. When I went to tune the antenna using the FTdx I got strange results. Above 7.300 MHz it nulls out and gives very low SWR. Below 7.300MHz I cannot tune the antenna at all and if I try to transmit at 20watts the radio tells me it is High SWR. I tried adjusting the whips on the two antennas (per the MFJ instructions) and could not get any change in the SWR readings.

I double checked all the connections and they were good. I also tried a suggestion from MFJ and made a balun of 8 turns of coax on a 6" form mounted at the feedpont. This did not show any changes either.

I am not sure what to do next. The reviews and reports about this dipole setup are all good and it should work well as assembled. Any help would be greatly appreciated.

Please help.

Thanks!

I didn't find the right solution from the Internet.

References www.arrl.org/forum/topics/view/2080

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