How to attach a 1/8" brass rod stock to an SO-239 chassis mount connector?

Discussion in 'Homebrew and Kit Projects' started by WF7A, Oct 25, 2008.

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  1. WF7A

    WF7A Subscriber QRZ Page

    The title asks it all: What would be the best way of doing that? I'm trying to build a 1/4" wave groundplane antenna for 127 MHz using 1/8" brass rods as elements. I tried a tap-and-die set to thread the rod stock for the four holes used to mount the connector to the chassis but brass being so soft, the nuts stripped the threads silly, so I suspect tack-welding them into the holes in my next option? (I thought of using a torch and solder, but I'm afraid I'll melt the insulator inside the connector.)

    The radiator's diameter is a little wider the than connector's center pin so again, same problem: how to attach it?

    After all is said and done, the antenna will be placed inside a PVC pipe cap then sealed with some kind of goo--any recommendations for that as well? (I thought of JB Weld since _nothing_ can get through that! :)
  2. VK2TIL

    VK2TIL Ham Member QRZ Page

    Use of a Teflon-insulated socket will help with the excess heat problem.

    For the radials, get or make four substantial eyelets (used in electrical work); solder each radial to an eyelet and bolt each to the SO-239.

    Or roll the end of each radial into a loop (if the brass is ductile) and attach with nuts/bolts/washers.

    For the vertical; solder is easy if you have a Teflon SO-239. It can be done with non-Teflon insulation; heat the rod, not the centre-pin, until the solder flows at the joint. You are, effectively, using the rod as the soldering iron "bit". A small gas torch will do.

    There are lots of other ways I can think of; the above seem simplest.

    I would use silicon sealer for the pipe cap housing.
    Last edited: Oct 25, 2008
  3. K9FV

    K9FV Ham Member QRZ Page

    Perfect way to attached the brass rod to the center pin is just as previous poster say.... If the brass rod does not bend easy to an eyelet, you might heat it red hot then dunk in water to cool - that's the way to aneal brass, while with steel/iron it makes brittle....

    Remember normal silicone RTV has acetic acid as the solvent......

    73 de Ken H>
  4. WF7A

    WF7A Subscriber QRZ Page

    Thanks, guys--great input! I was desperate and picked up an SO-239 chassis mount connector from *ugh* Radio Shack, so I'm pretty sure there's no Teflon in there.

    I take it the "eyelets" are ring terminals, but if not I'll find out when I go to Gnome Depot tomorrow.

    Thanks again!
  5. VK2TIL

    VK2TIL Ham Member QRZ Page

    "Ring terminal" sounds about right.

    You could make some; a short (1" or so) strip of brass (1/4" or so wide) with a hole in one end.

    The centre vertical/pin connection could be "sleeved" with brass tube as sold by hobby shops.

    The problem with soldering cheap connectors often comes from the metal they're made-from and/or the plating. You heat & heat and the @#^* solder won't take; then the insulation collapses. :(

    If you can avoid soldering to the body of the RS connector you will have less trouble. The pin should solder OK if clean.

    The ARRL has details of a ground-plane vertical;

    A similar design appears in the Antenna Book.
  6. WF7A

    WF7A Subscriber QRZ Page

    The sleeve is a great idea...though it'll cost me more in fuel to buy it than the tubing (the nearest hobby store is about 80 km from here). :S

    The Wifoid is going to laugh at me:

    "So, how much did your two-dollar antenna cost when all was said and done?"

    "Oh, about thirty."
  7. VK2TIL

    VK2TIL Ham Member QRZ Page

    I share your pain; "odd" things are difficult to get where I live, too.

    Over the years I have followed the practice of buying several items when I only need one; my junquebox is huge!!

    The upside is that I can make most things from materials/parts that I already have.

    We know what many others don't; it's not about $$$, it's about satisfaction, learning and a few other things.

    "I made it myself"; a wonderful phrase.
  8. ZL3GSL

    ZL3GSL Ham Member QRZ Page

    If the rod is too big to fit in the centre of the socket, file it until it does. ;)
  9. KR2D

    KR2D Ham Member QRZ Page

    Or use it as an excuse to buy a lathe. One can never have too many tools ;)
  10. N5RLR

    N5RLR Ham Member QRZ Page

    Tell her that it's good ol' American capitalism at it's best: High labor cost for an inexpensive item. :p

    A bench grinder can be handy for dressing down the diameter of rod stock to fit into the center pin of an SO-239. I've done this with welding-rod λ/4 2m groundplanes. :cool:

    Also, an SO-239 bulkhead jack mounted to a large fender washer can work. This would offer room to use larger screws to accommodate a loop bent into the end of a ground radial.

    Make a downtube from 5/8" ID tubing; hose-clamp this over the body of the PL-259 connecting to the groundplane. Also use hose clamps to attach the downtube to a mast.

    Whoops...we may be edging toward $45-$50, now... :D

    But...I wouldn't recommend using JB Weld. It contains iron/metal powder, which may "excite" in the presence of RF [you didn't say if the antenna was to be for transmit; if only for receive, then this point may be moot].
    Last edited: Nov 1, 2008
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