Wednesday, October 28, 2015

Time to look inside the MFJ 1788

Taking a close look at things
It's the fall and time for some antenna maintenance for me there is no tower to climb or any outdoor work for that matter. It's as simple as bringing the MFJ 1788 indoors from my balcony and having a look. I have had the cover of the antenna off in the past so it was no problem to quickly remove it and start investigating. Some of the things I look for are poor solder joints, little critters who have made my antenna home, the smooth operation of the tuning capacitor and the over all health of the components.  It was a good thing I did check the mechanical connections and without exaggerating I have to say that almost all nuts were
Checking the cap fins
loose......some very alarmingly loose! The hardware holding the stepper motor in place was the worst but not far behind was the larger nuts that held the large tuning capacitor in place. I can't remember the antenna acting funky at all but I do believe it was just a matter of time before something reared it's ugly head like a quirky SWR! Another thing I like to do while the antenna is apart and fully cycle the tuning capacitor for not only smooth operation but the equal spacing of the moving fins along side the stationary fins. There was only some minor adjustments needed to the capacitor fins.........BUT where does "Murphy"  fit into this adventure........well just as I was finishing my adjustments the antenna slipped off the TV tables I had it on and the control wire that runs the motor broke off the circuit board! Also the "feed loop" wire was distorted somewhat. The feed loop is 10
Some of the many nuts that were very loose.
Control wire torn off.
gauge wire in the antenna that is contorted into a egg shape, this little baby can really play games with how the SWR outcome on the loop is determined. I played with it when I first got the loop and that was a mistake as it occupied about 2 hours of my time to get the antenna's SWR back to "normal". I vowed to never touch that feed loop again, but thanks to Murphy it seems I have to revisit that dark cave again. I re-soldered the stepper motor wires back in place and did my best with the feed loop wire. The antenna was put back together and with my fingers cross I tested it and to my utter surprise the unit was working better than it has in the past.

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