Reparing old MFJ Goliath Tri-Mag mount

This is the second of these types of mounts I have had. I bought two, one with an SO-239 mount and one with a 3/8x24 mount. The 3/8x24 mount broke last year some time and was not repairable. The SO-239 mount stayed in constant service for 4-5 years... until the Thursday before Christmas. I backed out of the driveway at my dad's house and my antenna snagged a tree (all my antennas snag it) and the antenna actually broke off the mount!

What happened was the aluminum bar that the SO-239 was mounted to corroded around the connector. If you don't know what happens to aluminum when it corrodes it turns to a white powder (actually, raw aluminum is also a powder - it has to be refined and melted in to its solid metallic form we all know). Obviously, a powder doesn't have any strength at all. So, all the force of the antenna staying up was on the connector. When I snagged the tree the antenna just broke right off.

The parts/materials I used for this repair are:
1 Chassis Mount SO-239 with a 4-hole flange
4 counter-sunk 6-32 bolts (I used 1" because I couldn't find 3/4" ones at Lowes)
5 6-32 nuts (4 to lock the SO-239 down and one more as a clamp for the coax shield)
3 short hot glue sticks (for weather sealing)
spool of flux-core solder

The tools I used are:
1 reversible/variable speed drill
drill bits - 1/4", 1/2", 1/8", and 9/64" (1/16"-1/2" set had all the sizes I used)
1 stiff steel brush for the drill (or you can use a hand held steel brush if you wish)
1 hot glue gun
1 small (1/8" wide or so) flat head screwdriver
1 medium size Philips head screwdriver
1 pair small standard vice-grip locking pliers
1 45w soldering iron (other wattages would probably work)

I didn't think to get any pictures of the mount before and while I did the repair, unfortunately. I wish I did.

1. Take the old cable off by removing the cable clamp.

2. Scrape out the corroded aluminum. I used a stiff steel brush attachment for my drill to do this. When I was done there was a 1/16" dip in the aluminum bar directly under where the antenna was mounted! The bar was still solid, so I figured I would go ahead with the repair. The corrosion was just on the surface.

3. Drill out what is left of the old SO-239 (unless you can remove it completely, I couldn't) in order for the new one to fit in place. Make sure you have enough room to clear the lip on the SO-239. I used a 1/2" drill and needed to round out the hole a bit to get my connector to clear.

4. Mount the new SO-239 on the top of the bar, with the center pin going down through the bar.

5. Drill the 4 holes in the aluminum bar for the mounting bolts. I used a 1/8" drill bit to start the holes in the bar, using the SO-239's holes as a guide. This way the drill spun easy and I didn't take any material out of the bolt holes. Then I took the SO-239 off and drilled the holes. When I was done I switched to a 9/64" bit to ream out the holes in order to clear the #6 bolts.

6. Stick 3 bolts in and use the 1/4" drill to counter sink the open hole. Work your way around the flange, take one more bolt out and put it in the hole you just countersunk.

7. Put the 4th bolt in and install the nuts. Tighten them down.

Re-install the coax.
NOTE: This would be a good time to replace the coax if you need to. If you do replace the coax (which I wanted to but didn't have enough left to do it) then REPLACE WITH A HIGHER QUALITY CABLE!!!! The stock MFJ cable is JUNK. It is worse than RG-58.

8. Twist and tin the braid.

9. Wrap the braid around one of the bolts and put a nut down over top of it.

10. Solder the center conductor to the pin of the SO-239.

Now is the time for the hot glue. The hot glue is to seal the connector and coax from the elements. This is what lead to the corrosion and broken mount in the first place.

11.Put a little bit of glue around the coax where the jacket stops.

12. Re-install the coax clamp.

13. Load up the whole underneath side of the mount with hot glue. Pile on as much as you think you need - make sure you don't leave any open holes as this will be an entry point for water. Don't forget to coat the nuts and exposed bolts too.

14. Install the antenna half way on the mount.

15. Load this area up with hot glue too. Start feeding the glue in to the gap as you tighten the antenna down. Work the glue gun around the base a little bit to ensure a good seal.

16. When the antenna is tight go around the base one more time to make sure you have a good seal.







Water (and now in the winter time - salt spray) is the enemy! You have to keep out the elements in order for your system to perform and last. I should have taken the time and effort to seal up the mount when I first got it - then I wouldn't be here with the repair in the first place. So, if you are getting one of these mounts please seal it! Also, if you can or are inclined to, replace the crap coax!

This weekend's wire antenna raising fun

I just got home from helping a buddy, Justin W1IX, put up a new antenna. This was a trip, starting at about 3:30 after the antenna was "assembled". You would think that a wire antenna is a simple antenna right? We built an 80m dipole. Simple enough - two 1/4w legs attached to a 1:1 balun at the center and a run of coax to the rig. No problem. Well, not exactly.

The first issue was raising the center. We had enough space to set it up as an inverted V, so that's what we did. We picked the highest, most centrally located tree for the center. I used a sling shot to shoot a lead fishing sinker with fishing line attached over a point in the tree. This took a long time. I got the line in the wrong spot 3 times in a row. Then, when I finally hit the right spot, the line broke when we hoisted up the rope. CRAP!

So, over to the store we went and got some higher strength fishing line (we used 8lb test at first and went up to 25lb test). By the time we got back it was dark. We are determined hams so we didn't let that stop us. This was about 5:30.

So, on went the new fishing line and we tried again to get the right spot in the tree. Another 3-4 attempts, dinner, and another two attempts later we got it. This time, the fishing line held great while hoisting up the rope. We even had to persuade the line a little bit with some force to get it through the branches.

Now the center was up with the legs dangling. Only, the legs were caught in more branches. So, we spent the next couple hours fishing the wire though branches and trying to bend branches out of the way. It was really a mess. We're determined Hams, though... right?

By the time we were all done (or, the antenna was up and ready to test) it was 11:00pm. WOW! where did the time go? I guess time flys when you're having fun.... or, freezing your hands because you can't wear gloves working with fishing line and wire? HEHE

So we went back in when it was all up and ran the analyzer on it. We cut the legs a bit long so we could adjust them. The SWR dip was right at the very bottom of 80 - 3.500. So, we went back out and shortened the legs a bit (6" or so) and got the antenna to resonate somewhere in the middle of the band.

All and all, the antenna works. It was an experience. I don't think "simple" wire antennas are that "simple" to begin with in most yards with trees hehehe - I've done a few other installations like this before. So, now Justin has a nice antenna to play with. I can't wait to have a yard to put up an antenna like that in hehehe - some day. Now, I wonder if we can work each other now (well), being only 8-10 miles apart? I would hope so.