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K0FRG

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MFJ Dipole whip problem Aug 2nd 2017, 18:50 5 1,703 on 5/8/17

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MFJ Dipole whip problem K0FRG on 5/8/17
Zack,

Thanks again for the advice.

That makes perfect sense. I thought it was odd that it occurred exactly at 7.300. I will try tuning each antenna separately and be much more careful with my tuning technique and search around a bit on different frequencies.

I bought each antenna at a different time some months apart so I don't think both are defective but probably both are good.


Bob
K0FRG
MFJ Dipole whip problem K0FRG on 5/8/17
W1VT
Thanks for the suggestions.
I took the dipole down and tested both the antennas vertically with 2, 1/4 wave radials. They both exhibited the same problem that I had before. Above 7.300 Mhz they would null and below that high SWR, I even tired two different feed lines to make sure that was not a problem. The only thing I can think at this point is that the antenna is near (within a few feet) of my house which is stucco. I am thinking that the screen mesh in the stucco is causing a problem. Other than that I am stumped and don't have a clue as to what to do next. These antennas should present a reasonable SWR to the tuner in the radio in either dipole or single vertical arrangement.
What else can I try?
MFJ Dipole whip problem K0FRG on 2/8/17
I have a FTdx1200 radio and have been having a problem with a new antenna system. Here are the details.

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.

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