MFJ-1775 Dipole Antenna

[W3XAF]

I purchased an MFJ-1775 rotatable dipole antenna and installed it on top of a Ham IV Rotor.

The dipole was very easy to put together and MFJ provided many spare parts with the MFJ-1775 kit.

The dipole consists of one 14-foot long aluminum element (tube) which has two coil assemblies attached to each end of the aluminum tube. #Each coil assembly consists of four coils, one coil each for 10, 15, 20 & 40 meters. #Connected to each coil is a metal ring which has four graphite spokes inserted into holes in the ring.

In order to create a resonant frequency on each band, one has to painstakingly cut each graphite spoke using an MFJ-259B SWR Analyzer until the resonant frequency is achieved. #That task took me about three hours.

After I hoisted the antenna into my Ham IV Rotor, and connected the RG-213 Coax to the antenna balun, I rechecked all the resonant frequencies and they had all changed. #This might have been due to the fact that I used five plastic covered steel guy wires to secure my antenna mast to the ground beneath.

I finally replaced all my guy wires with 3/8" Dacron rope and then had to re-cut the antenna spokes to the required resonant frequencies for each band. #No easy task standing on a sloping roof 50 feet above the ground.
Furthermore, I found it necessary to order more 30"-long spokes from MFJ in order to achieve the 40 Meter resonant frequency I needed.

I then ran into a major problem. #When I applied power to my antenna and tuned up using my FT-1000MP Mark IV Transceiver, AL-80B Amplifier and MFJ 989D Tuner, I found that the resonant frequencies for each band were not the same as those I had established with my MFJ-259B SWR Analyzer. #Therefore, I had to go back up on my roof and re-cut or lengthen the graphite spokes accordingly. #This task took many days!!!

The only other problem I have experienced now that the antenna spokes are all cut for the resonant frequencies that I want to operate on, is that when I use voice modulation my SWR varies between 1:1 and 1:4 depending on how long I speak into the microphone. #The longer I speak into my microphone, the higher the SWR goes. This problem may be the result of my balun overheating?

[W3XAF]

It's been over a year now that I constructed & installed my MFJ-1775 Rotatable Dipole. So far, I've burned up three different coil assemblies.

Hy-Gain, who now has control over all MFJ antennas, has sent me new coil assemblies because my antenna was still under warranty.

The problem seems to be with the 20-Meter coil. For some reason the fiberglass tube that the coil is wrapped on will eventually burn up and this leaves a rather large hole in the tube. After the hole is formed, my 20-Meter SWR shoots up and I can't use the 20-Meter band any longer.

Hy-Gain thinks that the problem is metallic impurities in the fiberglass tubes.