RS mag-mount scanner antenna "fix"

izzyj4 · #1 (**permalink**) 10-28-2009, 10:26 PM

Well I started to work on my antenna farm which is going in my attic (just scanning, no ham stuff yet, still studying for my test). Well the first project was to try modify my old Radio Shack mag-mount antenna for local use. My plan was to wither remove the supplied coaxial cable and replace it with a single feed of RG-8 or to cut the coaxial and (GASP) replace the connectors to hook up the RG-8. Well that plan hit a snag right off the bat when I tried to remove the top element holder from the base screw.

Well the next thing I did was removed the bottom plastic covering that protected the magnet and from your car from being scratched, low and behold I came across a bunch of rush. (UGGGGG!!!!) After cleaning the rust chips off the magnet, I knew what the problem was now, the rusty screw. Shame on me for leaving it out in the garage last winter.

The first thing I tried to do was to use "liquid wrench", "goof-off" and such to try and loosen up the bolt from the element housing......no luck. The last resort and something that I really didn't want to do was to hack off the plastic housing. Finally after removing all of the housing I found that the screw and bolt holding the feed line and element were totally rusted. I tried again with the trust rust remover stuff and again no go, I ended up snapping the bolt in half while trying to loosen the bolt. Time for Plan B.

I ended up drilling out the bolt from the element holder, thus ruining the threads inside at the base of the holder. The next step was to start cleaning up the parts, the base, ect. Not too bad, a little CLR and a steel brush helped get off some of the rust and corrosion. Next step was to re-thread the element holder and find a new bolt. After measuring it up and finding a bolt, I threaded the holder for 18 - 15/16. I re-used the plastic spacers that were used with the original bolt, which had a lot of meat on them. To make sure I had the correct inside diameter for the new bolt, I first threaded the plastic with my tap and then filed down the inside of the plastic until the threads disappeared and they slipped on the bolt perfectly.

I then re-assembled the base (minus the plastic housing of course) with the original cable and hooked it up to one of my scanners to test it. So far so good for local stuff but I'm gonna have to spend some time listening for father away stations. It sound like its picking up better than before since I removed the rusty bolt and now have a better contact. We'll see what happens.

I do have some pictures that I took while doing this "fix" which I will post up tomorrow (getting up at 5am for a hour ride to work is not too fun). Granted its not pretty by far, but it would be in the attic and somewhat protected. I'm going to look and see if I can make some sort of housing for the guts to protect it better in case.

I'll let you all know how I make out. Also if there are any suggestions, it would be greatly appreciated.

conve36 · #2 (**permalink**) 10-29-2009, 01:00 PM

Dont worry, I have had similar problems with the same antenna (actually twice). What you should do is throw away everything BUT the magnet and the metal piece that hold the antenna rod (keeps the plastic washer too. Simply replace the cable with some quad-shield RG-6 (75ohm is great for scanning, trust me). Make sure when done to test the end of coax that plugs into scanner for any shorts. It is very easy to short out the antenna at the base when connecting the new cable. Who cares about the plastic housing, when satisfied, just goop all over it some silicone sealant or other kind of sealer. Have fun experimenting with different size rods for better performance on certain frequencies. Ill try and take some pics of my mutilated (but working great) mag-mount antennas.

izzyj4 · #3 (**permalink**) 10-29-2009, 09:35 PM

Thanks conve36 for the info but I like to tinker a bit too! So far its working pretty good, I'm actually picking up Suffolk County MED COM 5 x 5 through it, granted I'm line of sight to the tower, about 150 to 200 ft. above sea level and 10 miles approx from the shore line.

Here is some pictures of what I did so far.

izzyj4 · #4 (**permalink**) 10-29-2009, 09:39 PM

Here is the finished side of it. I'm thinking if this works out for me, mounting a SO-239 coax connector to it since my coax already has a PL-259 connector on it so I can remove it if I need to replace / move it. My other antenna is a Diamond D-130J.

gewecke · #5 (**permalink**) 10-30-2009, 02:08 AM

Well it's not pretty,but if it works!

N9ZAS

conve36 · #6 (**permalink**) 10-30-2009, 05:55 PM

I wouldve sanded off the rust with a wire brush, to try and prevent further rusting... But looks great! Just make sure your using a "ground-plane". Ive used upside down round cake pans and they worked perfect.

izzyj4 · #7 (**permalink**) 10-31-2009, 11:34 AM

I'm gonna clean it up a bit more too once I decide what else I'm going to do with it. I was getting a little tired and the wire brush I was using wasn't doing quite a good job. Need to run to the hardware store and get a true wire brush for the job.

I ran it for a few hours without a plane and it picked up pretty well, just did that as a test to see if it actually worked. I had a old metal shelf system that was FUBAR so I took of a shelf and used that as the ground plain and I'm getting a lot better results of course.

I'm still thinking on putting the SO-239 connector on it instead of soldering the wire directly to it in case I decide to replace it, ect. I'm worried about placement of the SO-239. I was thinking to soldering it to the upright holder and the base fitting it square up against them. Also I was going to make a "wire relief" holder out of plastic to keep the wire in line and prevent stress to the wire and the antenna system. Do you all think that would work okay or would it be overkill.

Thanks for all the input

izzyj4 · #8 (**permalink**) 11-13-2009, 10:34 AM

Hey all,

Just an update. I redid the wiring with a short piece of RG-59 that came with it originally and added the SO-239 connector so I can move / replace the antenna if I need too. I checked to make sure that I made the correct connections and decided not to tack the connector to the base, I just wrapped it with some electrical tape to protect the connections. I have it up in the attic now and finishing snaking the wire down to my listening post. Since this is my "local" antenna I'm not too concerned with a lot of signal loss. Most of the towers for the area are line-of-sight to my home. I'll post some more pictures later of the finish product.